14、Redis的复制

写在前面的话：读书破万卷，编码如有神

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1、复制

Redis支持复制的功能，以实现当一台服务器的数据更新后，自动将新的数据同步到其它数据库。

Redis复制实现中，把数据库分为主数据库master和从数据库slave,主数据库可以进行读写操作，从数据库一般只是读的，当主数据库数据变化的时候，会自动同步给从数据库。

2、复制带来的好处

（1）可以实现读写分离

（2）利于在主数据库崩溃时进行数据恢复

3、复制的配置

主数据库不配置，从数据库需要在配置中设置： slaveof 主数据库ip 主数据库端口

先来简单体会下：1个主数据库、1个从数据库

3.1、主数据库redis.conf的配置如下

 # Redis configuration file example.

 #

 # Note that in order to read the configuration file, Redis must be

 # started with the file path as first argument:

 #

 # ./redis-server /path/to/redis.conf

 # Note on units: when memory size is needed, it is possible to specify

 # it in the usual form of 1k 5GB 4M and so forth:

 #

 # 1k => 1000 bytes

 # 1kb => 1024 bytes

 # 1m => 1000000 bytes

 # 1mb => 1024*1024 bytes

 # 1g => 1000000000 bytes

 # 1gb => 1024*1024*1024 bytes

 #

 # units are case insensitive so 1GB 1Gb 1gB are all the same.

 ################################## INCLUDES ###################################

 # Include one or more other config files here.  This is useful if you

 # have a standard template that goes to all Redis servers but also need

 # to customize a few per-server settings.  Include files can include

 # other files, so use this wisely.

 #

 # Notice option "include" won't be rewritten by command "CONFIG REWRITE"

 # from admin or Redis Sentinel. Since Redis always uses the last processed

 # line as value of a configuration directive, you'd better put includes

 # at the beginning of this file to avoid overwriting config change at runtime.

 #

 # If instead you are interested in using includes to override configuration

 # options, it is better to use include as the last line.

 #

 # include /path/to/local.conf

 # include /path/to/other.conf

 ################################## MODULES #####################################

 # Load modules at startup. If the server is not able to load modules

 # it will abort. It is possible to use multiple loadmodule directives.

 #

 # loadmodule /path/to/my_module.so

 # loadmodule /path/to/other_module.so

 ################################## NETWORK #####################################

 # By default, if no "bind" configuration directive is specified, Redis listens

 # for connections from all the network interfaces available on the server.

 # It is possible to listen to just one or multiple selected interfaces using

 # the "bind" configuration directive, followed by one or more IP addresses.

 #

 # Examples:

 #

 # bind 192.168.1.100 10.0.0.1

 # bind 127.0.0.1 ::1

 #

 # ~~~ WARNING ~~~ If the computer running Redis is directly exposed to the

 # internet, binding to all the interfaces is dangerous and will expose the

 # instance to everybody on the internet. So by default we uncomment the

 # following bind directive, that will force Redis to listen only into

 # the IPv4 lookback interface address (this means Redis will be able to

 # accept connections only from clients running into the same computer it

 # is running).

 #

 # IF YOU ARE SURE YOU WANT YOUR INSTANCE TO LISTEN TO ALL THE INTERFACES

 # JUST COMMENT THE FOLLOWING LINE.

 # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 bind 127.0.0.1

 # Protected mode is a layer of security protection, in order to avoid that

 # Redis instances left open on the internet are accessed and exploited.

 #

 # When protected mode is on and if:

 #

 # 1) The server is not binding explicitly to a set of addresses using the

 #    "bind" directive.

 # 2) No password is configured.

 #

 # The server only accepts connections from clients connecting from the

 # IPv4 and IPv6 loopback addresses 127.0.0.1 and ::1, and from Unix domain

 # sockets.

 #

 # By default protected mode is enabled. You should disable it only if

 # you are sure you want clients from other hosts to connect to Redis

 # even if no authentication is configured, nor a specific set of interfaces

 # are explicitly listed using the "bind" directive.

 protected-mode yes

 # Accept connections on the specified port, default is 6379 (IANA #815344).

 # If port 0 is specified Redis will not listen on a TCP socket.

 port 6379

 # TCP listen() backlog.

 #

 # In high requests-per-second environments you need an high backlog in order

 # to avoid slow clients connections issues. Note that the Linux kernel

 # will silently truncate it to the value of /proc/sys/net/core/somaxconn so

 # make sure to raise both the value of somaxconn and tcp_max_syn_backlog

 # in order to get the desired effect.

 tcp-backlog 511

 # Unix socket.

 #

 # Specify the path for the Unix socket that will be used to listen for

 # incoming connections. There is no default, so Redis will not listen

 # on a unix socket when not specified.

 #

 # unixsocket /tmp/redis.sock

 # unixsocketperm 700

 # Close the connection after a client is idle for N seconds (0 to disable)

 timeout 0

 # TCP keepalive.

 #

 # If non-zero, use SO_KEEPALIVE to send TCP ACKs to clients in absence

 # of communication. This is useful for two reasons:

 #

 # 1) Detect dead peers.

 # 2) Take the connection alive from the point of view of network

 #    equipment in the middle.

 #

 # On Linux, the specified value (in seconds) is the period used to send ACKs.

 # Note that to close the connection the double of the time is needed.

 # On other kernels the period depends on the kernel configuration.

 #

 # A reasonable value for this option is 300 seconds, which is the new

 # Redis default starting with Redis 3.2.1.

 tcp-keepalive 300

 ################################# GENERAL #####################################

 # By default Redis does not run as a daemon. Use 'yes' if you need it.

 # Note that Redis will write a pid file in /var/run/redis.pid when daemonized.

 daemonize yes

 # If you run Redis from upstart or systemd, Redis can interact with your

 # supervision tree. Options:

 #   supervised no      - no supervision interaction

 #   supervised upstart - signal upstart by putting Redis into SIGSTOP mode

 #   supervised systemd - signal systemd by writing READY=1 to $NOTIFY_SOCKET

 #   supervised auto    - detect upstart or systemd method based on

 #                        UPSTART_JOB or NOTIFY_SOCKET environment variables

 # Note: these supervision methods only signal "process is ready."

 #       They do not enable continuous liveness pings back to your supervisor.

 supervised no

 # If a pid file is specified, Redis writes it where specified at startup

 # and removes it at exit.

 #

 # When the server runs non daemonized, no pid file is created if none is

 # specified in the configuration. When the server is daemonized, the pid file

 # is used even if not specified, defaulting to "/var/run/redis.pid".

 #

 # Creating a pid file is best effort: if Redis is not able to create it

 # nothing bad happens, the server will start and run normally.

 pidfile /var/run/redis_6379.pid

 # Specify the server verbosity level.

 # This can be one of:

 # debug (a lot of information, useful for development/testing)

 # verbose (many rarely useful info, but not a mess like the debug level)

 # notice (moderately verbose, what you want in production probably)

 # warning (only very important / critical messages are logged)

 loglevel notice

 # Specify the log file name. Also the empty string can be used to force

 # Redis to log on the standard output. Note that if you use standard

 # output for logging but daemonize, logs will be sent to /dev/null

 logfile "redis_6379.log"

 # To enable logging to the system logger, just set 'syslog-enabled' to yes,

 # and optionally update the other syslog parameters to suit your needs.

 # syslog-enabled no

 # Specify the syslog identity.

 # syslog-ident redis

 # Specify the syslog facility. Must be USER or between LOCAL0-LOCAL7.

 # syslog-facility local0

 # Set the number of databases. The default database is DB 0, you can select

 # a different one on a per-connection basis using SELECT <dbid> where

 # dbid is a number between 0 and 'databases'-1

 databases 16

 # By default Redis shows an ASCII art logo only when started to log to the

 # standard output and if the standard output is a TTY. Basically this means

 # that normally a logo is displayed only in interactive sessions.

 #

 # However it is possible to force the pre-4.0 behavior and always show a

 # ASCII art logo in startup logs by setting the following option to yes.

 always-show-logo yes

 ################################ SNAPSHOTTING  ################################

 #

 # Save the DB on disk:

 #

 #   save <seconds> <changes>

 #

 #   Will save the DB if both the given number of seconds and the given

 #   number of write operations against the DB occurred.

 #

 #   In the example below the behaviour will be to save:

 #   after 900 sec (15 min) if at least 1 key changed

 #   after 300 sec (5 min) if at least 10 keys changed

 #   after 60 sec if at least 10000 keys changed

 #

 #   Note: you can disable saving completely by commenting out all "save" lines.

 #

 #   It is also possible to remove all the previously configured save

 #   points by adding a save directive with a single empty string argument

 #   like in the following example:

 #

 #   save ""

 save 900 1

 save 300 10

 save 60 10000

 # By default Redis will stop accepting writes if RDB snapshots are enabled

 # (at least one save point) and the latest background save failed.

 # This will make the user aware (in a hard way) that data is not persisting

 # on disk properly, otherwise chances are that no one will notice and some

 # disaster will happen.

 #

 # If the background saving process will start working again Redis will

 # automatically allow writes again.

 #

 # However if you have setup your proper monitoring of the Redis server

 # and persistence, you may want to disable this feature so that Redis will

 # continue to work as usual even if there are problems with disk,

 # permissions, and so forth.

 stop-writes-on-bgsave-error yes

 # Compress string objects using LZF when dump .rdb databases?

 # For default that's set to 'yes' as it's almost always a win.

 # If you want to save some CPU in the saving child set it to 'no' but

 # the dataset will likely be bigger if you have compressible values or keys.

 rdbcompression yes

 # Since version 5 of RDB a CRC64 checksum is placed at the end of the file.

 # This makes the format more resistant to corruption but there is a performance

 # hit to pay (around 10%) when saving and loading RDB files, so you can disable it

 # for maximum performances.

 #

 # RDB files created with checksum disabled have a checksum of zero that will

 # tell the loading code to skip the check.

 rdbchecksum yes

 # The filename where to dump the DB

 dbfilename dump_6379.rdb

 # The working directory.

 #

 # The DB will be written inside this directory, with the filename specified

 # above using the 'dbfilename' configuration directive.

 #

 # The Append Only File will also be created inside this directory.

 #

 # Note that you must specify a directory here, not a file name.

 dir ./

 ################################# REPLICATION #################################

 # Master-Slave replication. Use slaveof to make a Redis instance a copy of

 # another Redis server. A few things to understand ASAP about Redis replication.

 #

 # 1) Redis replication is asynchronous, but you can configure a master to

 #    stop accepting writes if it appears to be not connected with at least

 #    a given number of slaves.

 # 2) Redis slaves are able to perform a partial resynchronization with the

 #    master if the replication link is lost for a relatively small amount of

 #    time. You may want to configure the replication backlog size (see the next

 #    sections of this file) with a sensible value depending on your needs.

 # 3) Replication is automatic and does not need user intervention. After a

 #    network partition slaves automatically try to reconnect to masters

 #    and resynchronize with them.

 #

 # slaveof <masterip> <masterport>

 # If the master is password protected (using the "requirepass" configuration

 # directive below) it is possible to tell the slave to authenticate before

 # starting the replication synchronization process, otherwise the master will

 # refuse the slave request.

 #

 # masterauth <master-password>

 # When a slave loses its connection with the master, or when the replication

 # is still in progress, the slave can act in two different ways:

 #

 # 1) if slave-serve-stale-data is set to 'yes' (the default) the slave will

 #    still reply to client requests, possibly with out of date data, or the

 #    data set may just be empty if this is the first synchronization.

 #

 # 2) if slave-serve-stale-data is set to 'no' the slave will reply with

 #    an error "SYNC with master in progress" to all the kind of commands

 #    but to INFO and SLAVEOF.

 #

 slave-serve-stale-data yes

 # You can configure a slave instance to accept writes or not. Writing against

 # a slave instance may be useful to store some ephemeral data (because data

 # written on a slave will be easily deleted after resync with the master) but

 # may also cause problems if clients are writing to it because of a

 # misconfiguration.

 #

 # Since Redis 2.6 by default slaves are read-only.

 #

 # Note: read only slaves are not designed to be exposed to untrusted clients

 # on the internet. It's just a protection layer against misuse of the instance.

 # Still a read only slave exports by default all the administrative commands

 # such as CONFIG, DEBUG, and so forth. To a limited extent you can improve

 # security of read only slaves using 'rename-command' to shadow all the

 # administrative / dangerous commands.

 slave-read-only yes

 # Replication SYNC strategy: disk or socket.

 #

 # -------------------------------------------------------

 # WARNING: DISKLESS REPLICATION IS EXPERIMENTAL CURRENTLY

 # -------------------------------------------------------

 #

 # New slaves and reconnecting slaves that are not able to continue the replication

 # process just receiving differences, need to do what is called a "full

 # synchronization". An RDB file is transmitted from the master to the slaves.

 # The transmission can happen in two different ways:

 #

 # 1) Disk-backed: The Redis master creates a new process that writes the RDB

 #                 file on disk. Later the file is transferred by the parent

 #                 process to the slaves incrementally.

 # 2) Diskless: The Redis master creates a new process that directly writes the

 #              RDB file to slave sockets, without touching the disk at all.

 #

 # With disk-backed replication, while the RDB file is generated, more slaves

 # can be queued and served with the RDB file as soon as the current child producing

 # the RDB file finishes its work. With diskless replication instead once

 # the transfer starts, new slaves arriving will be queued and a new transfer

 # will start when the current one terminates.

 #

 # When diskless replication is used, the master waits a configurable amount of

 # time (in seconds) before starting the transfer in the hope that multiple slaves

 # will arrive and the transfer can be parallelized.

 #

 # With slow disks and fast (large bandwidth) networks, diskless replication

 # works better.

 repl-diskless-sync no

 # When diskless replication is enabled, it is possible to configure the delay

 # the server waits in order to spawn the child that transfers the RDB via socket

 # to the slaves.

 #

 # This is important since once the transfer starts, it is not possible to serve

 # new slaves arriving, that will be queued for the next RDB transfer, so the server

 # waits a delay in order to let more slaves arrive.

 #

 # The delay is specified in seconds, and by default is 5 seconds. To disable

 # it entirely just set it to 0 seconds and the transfer will start ASAP.

 repl-diskless-sync-delay 5

 # Slaves send PINGs to server in a predefined interval. It's possible to change

 # this interval with the repl_ping_slave_period option. The default value is 10

 # seconds.

 #

 # repl-ping-slave-period 10

 # The following option sets the replication timeout for:

 #

 # 1) Bulk transfer I/O during SYNC, from the point of view of slave.

 # 2) Master timeout from the point of view of slaves (data, pings).

 # 3) Slave timeout from the point of view of masters (REPLCONF ACK pings).

 #

 # It is important to make sure that this value is greater than the value

 # specified for repl-ping-slave-period otherwise a timeout will be detected

 # every time there is low traffic between the master and the slave.

 #

 # repl-timeout 60

 # Disable TCP_NODELAY on the slave socket after SYNC?

 #

 # If you select "yes" Redis will use a smaller number of TCP packets and

 # less bandwidth to send data to slaves. But this can add a delay for

 # the data to appear on the slave side, up to 40 milliseconds with

 # Linux kernels using a default configuration.

 #

 # If you select "no" the delay for data to appear on the slave side will

 # be reduced but more bandwidth will be used for replication.

 #

 # By default we optimize for low latency, but in very high traffic conditions

 # or when the master and slaves are many hops away, turning this to "yes" may

 # be a good idea.

 repl-disable-tcp-nodelay no

 # Set the replication backlog size. The backlog is a buffer that accumulates

 # slave data when slaves are disconnected for some time, so that when a slave

 # wants to reconnect again, often a full resync is not needed, but a partial

 # resync is enough, just passing the portion of data the slave missed while

 # disconnected.

 #

 # The bigger the replication backlog, the longer the time the slave can be

 # disconnected and later be able to perform a partial resynchronization.

 #

 # The backlog is only allocated once there is at least a slave connected.

 #

 # repl-backlog-size 1mb

 # After a master has no longer connected slaves for some time, the backlog

 # will be freed. The following option configures the amount of seconds that

 # need to elapse, starting from the time the last slave disconnected, for

 # the backlog buffer to be freed.

 #

 # Note that slaves never free the backlog for timeout, since they may be

 # promoted to masters later, and should be able to correctly "partially

 # resynchronize" with the slaves: hence they should always accumulate backlog.

 #

 # A value of 0 means to never release the backlog.

 #

 # repl-backlog-ttl 3600

 # The slave priority is an integer number published by Redis in the INFO output.

 # It is used by Redis Sentinel in order to select a slave to promote into a

 # master if the master is no longer working correctly.

 #

 # A slave with a low priority number is considered better for promotion, so

 # for instance if there are three slaves with priority 10, 100, 25 Sentinel will

 # pick the one with priority 10, that is the lowest.

 #

 # However a special priority of 0 marks the slave as not able to perform the

 # role of master, so a slave with priority of 0 will never be selected by

 # Redis Sentinel for promotion.

 #

 # By default the priority is 100.

 slave-priority 100

 # It is possible for a master to stop accepting writes if there are less than

 # N slaves connected, having a lag less or equal than M seconds.

 #

 # The N slaves need to be in "online" state.

 #

 # The lag in seconds, that must be <= the specified value, is calculated from

 # the last ping received from the slave, that is usually sent every second.

 #

 # This option does not GUARANTEE that N replicas will accept the write, but

 # will limit the window of exposure for lost writes in case not enough slaves

 # are available, to the specified number of seconds.

 #

 # For example to require at least 3 slaves with a lag <= 10 seconds use:

 #

 # min-slaves-to-write 3

 # min-slaves-max-lag 10

 #

 # Setting one or the other to 0 disables the feature.

 #

 # By default min-slaves-to-write is set to 0 (feature disabled) and

 # min-slaves-max-lag is set to 10.

 # A Redis master is able to list the address and port of the attached

 # slaves in different ways. For example the "INFO replication" section

 # offers this information, which is used, among other tools, by

 # Redis Sentinel in order to discover slave instances.

 # Another place where this info is available is in the output of the

 # "ROLE" command of a master.

 #

 # The listed IP and address normally reported by a slave is obtained

 # in the following way:

 #

 #   IP: The address is auto detected by checking the peer address

 #   of the socket used by the slave to connect with the master.

 #

 #   Port: The port is communicated by the slave during the replication

 #   handshake, and is normally the port that the slave is using to

 #   list for connections.

 #

 # However when port forwarding or Network Address Translation (NAT) is

 # used, the slave may be actually reachable via different IP and port

 # pairs. The following two options can be used by a slave in order to

 # report to its master a specific set of IP and port, so that both INFO

 # and ROLE will report those values.

 #

 # There is no need to use both the options if you need to override just

 # the port or the IP address.

 #

 # slave-announce-ip 5.5.5.5

 # slave-announce-port 1234

 ################################## SECURITY ###################################

 # Require clients to issue AUTH <PASSWORD> before processing any other

 # commands.  This might be useful in environments in which you do not trust

 # others with access to the host running redis-server.

 #

 # This should stay commented out for backward compatibility and because most

 # people do not need auth (e.g. they run their own servers).

 #

 # Warning: since Redis is pretty fast an outside user can try up to

 # 150k passwords per second against a good box. This means that you should

 # use a very strong password otherwise it will be very easy to break.

 #

 # requirepass foobared

 # Command renaming.

 #

 # It is possible to change the name of dangerous commands in a shared

 # environment. For instance the CONFIG command may be renamed into something

 # hard to guess so that it will still be available for internal-use tools

 # but not available for general clients.

 #

 # Example:

 #

 # rename-command CONFIG b840fc02d524045429941cc15f59e41cb7be6c52

 #

 # It is also possible to completely kill a command by renaming it into

 # an empty string:

 #

 # rename-command CONFIG ""

 #

 # Please note that changing the name of commands that are logged into the

 # AOF file or transmitted to slaves may cause problems.

 ################################### CLIENTS ####################################

 # Set the max number of connected clients at the same time. By default

 # this limit is set to 10000 clients, however if the Redis server is not

 # able to configure the process file limit to allow for the specified limit

 # the max number of allowed clients is set to the current file limit

 # minus 32 (as Redis reserves a few file descriptors for internal uses).

 #

 # Once the limit is reached Redis will close all the new connections sending

 # an error 'max number of clients reached'.

 #

 # maxclients 10000

 ############################## MEMORY MANAGEMENT ################################

 # Set a memory usage limit to the specified amount of bytes.

 # When the memory limit is reached Redis will try to remove keys

 # according to the eviction policy selected (see maxmemory-policy).

 #

 # If Redis can't remove keys according to the policy, or if the policy is

 # set to 'noeviction', Redis will start to reply with errors to commands

 # that would use more memory, like SET, LPUSH, and so on, and will continue

 # to reply to read-only commands like GET.

 #

 # This option is usually useful when using Redis as an LRU or LFU cache, or to

 # set a hard memory limit for an instance (using the 'noeviction' policy).

 #

 # WARNING: If you have slaves attached to an instance with maxmemory on,

 # the size of the output buffers needed to feed the slaves are subtracted

 # from the used memory count, so that network problems / resyncs will

 # not trigger a loop where keys are evicted, and in turn the output

 # buffer of slaves is full with DELs of keys evicted triggering the deletion

 # of more keys, and so forth until the database is completely emptied.

 #

 # In short... if you have slaves attached it is suggested that you set a lower

 # limit for maxmemory so that there is some free RAM on the system for slave

 # output buffers (but this is not needed if the policy is 'noeviction').

 #

 # maxmemory <bytes>

 # MAXMEMORY POLICY: how Redis will select what to remove when maxmemory

 # is reached. You can select among five behaviors:

 #

 # volatile-lru -> Evict using approximated LRU among the keys with an expire set.

 # allkeys-lru -> Evict any key using approximated LRU.

 # volatile-lfu -> Evict using approximated LFU among the keys with an expire set.

 # allkeys-lfu -> Evict any key using approximated LFU.

 # volatile-random -> Remove a random key among the ones with an expire set.

 # allkeys-random -> Remove a random key, any key.

 # volatile-ttl -> Remove the key with the nearest expire time (minor TTL)

 # noeviction -> Don't evict anything, just return an error on write operations.

 #

 # LRU means Least Recently Used

 # LFU means Least Frequently Used

 #

 # Both LRU, LFU and volatile-ttl are implemented using approximated

 # randomized algorithms.

 #

 # Note: with any of the above policies, Redis will return an error on write

 #       operations, when there are no suitable keys for eviction.

 #

 #       At the date of writing these commands are: set setnx setex append

 #       incr decr rpush lpush rpushx lpushx linsert lset rpoplpush sadd

 #       sinter sinterstore sunion sunionstore sdiff sdiffstore zadd zincrby

 #       zunionstore zinterstore hset hsetnx hmset hincrby incrby decrby

 #       getset mset msetnx exec sort

 #

 # The default is:

 #

 # maxmemory-policy noeviction

 # LRU, LFU and minimal TTL algorithms are not precise algorithms but approximated

 # algorithms (in order to save memory), so you can tune it for speed or

 # accuracy. For default Redis will check five keys and pick the one that was

 # used less recently, you can change the sample size using the following

 # configuration directive.

 #

 # The default of 5 produces good enough results. 10 Approximates very closely

 # true LRU but costs more CPU. 3 is faster but not very accurate.

 #

 # maxmemory-samples 5

 ############################# LAZY FREEING ####################################

 # Redis has two primitives to delete keys. One is called DEL and is a blocking

 # deletion of the object. It means that the server stops processing new commands

 # in order to reclaim all the memory associated with an object in a synchronous

 # way. If the key deleted is associated with a small object, the time needed

 # in order to execute the DEL command is very small and comparable to most other

 # O(1) or O(log_N) commands in Redis. However if the key is associated with an

 # aggregated value containing millions of elements, the server can block for

 # a long time (even seconds) in order to complete the operation.

 #

 # For the above reasons Redis also offers non blocking deletion primitives

 # such as UNLINK (non blocking DEL) and the ASYNC option of FLUSHALL and

 # FLUSHDB commands, in order to reclaim memory in background. Those commands

 # are executed in constant time. Another thread will incrementally free the

 # object in the background as fast as possible.

 #

 # DEL, UNLINK and ASYNC option of FLUSHALL and FLUSHDB are user-controlled.

 # It's up to the design of the application to understand when it is a good

 # idea to use one or the other. However the Redis server sometimes has to

 # delete keys or flush the whole database as a side effect of other operations.

 # Specifically Redis deletes objects independently of a user call in the

 # following scenarios:

 #

 # 1) On eviction, because of the maxmemory and maxmemory policy configurations,

 #    in order to make room for new data, without going over the specified

 #    memory limit.

 # 2) Because of expire: when a key with an associated time to live (see the

 #    EXPIRE command) must be deleted from memory.

 # 3) Because of a side effect of a command that stores data on a key that may

 #    already exist. For example the RENAME command may delete the old key

 #    content when it is replaced with another one. Similarly SUNIONSTORE

 #    or SORT with STORE option may delete existing keys. The SET command

 #    itself removes any old content of the specified key in order to replace

 #    it with the specified string.

 # 4) During replication, when a slave performs a full resynchronization with

 #    its master, the content of the whole database is removed in order to

 #    load the RDB file just transfered.

 #

 # In all the above cases the default is to delete objects in a blocking way,

 # like if DEL was called. However you can configure each case specifically

 # in order to instead release memory in a non-blocking way like if UNLINK

 # was called, using the following configuration directives:

 lazyfree-lazy-eviction no

 lazyfree-lazy-expire no

 lazyfree-lazy-server-del no

 slave-lazy-flush no

 ############################## APPEND ONLY MODE ###############################

 # By default Redis asynchronously dumps the dataset on disk. This mode is

 # good enough in many applications, but an issue with the Redis process or

 # a power outage may result into a few minutes of writes lost (depending on

 # the configured save points).

 #

 # The Append Only File is an alternative persistence mode that provides

 # much better durability. For instance using the default data fsync policy

 # (see later in the config file) Redis can lose just one second of writes in a

 # dramatic event like a server power outage, or a single write if something

 # wrong with the Redis process itself happens, but the operating system is

 # still running correctly.

 #

 # AOF and RDB persistence can be enabled at the same time without problems.

 # If the AOF is enabled on startup Redis will load the AOF, that is the file

 # with the better durability guarantees.

 #

 # Please check http://redis.io/topics/persistence for more information.

 appendonly no

 # The name of the append only file (default: "appendonly.aof")

 appendfilename "appendonly6379.aof"

 # The fsync() call tells the Operating System to actually write data on disk

 # instead of waiting for more data in the output buffer. Some OS will really flush

 # data on disk, some other OS will just try to do it ASAP.

 #

 # Redis supports three different modes:

 #

 # no: don't fsync, just let the OS flush the data when it wants. Faster.

 # always: fsync after every write to the append only log. Slow, Safest.

 # everysec: fsync only one time every second. Compromise.

 #

 # The default is "everysec", as that's usually the right compromise between

 # speed and data safety. It's up to you to understand if you can relax this to

 # "no" that will let the operating system flush the output buffer when

 # it wants, for better performances (but if you can live with the idea of

 # some data loss consider the default persistence mode that's snapshotting),

 # or on the contrary, use "always" that's very slow but a bit safer than

 # everysec.

 #

 # More details please check the following article:

 # http://antirez.com/post/redis-persistence-demystified.html

 #

 # If unsure, use "everysec".

 # appendfsync always

 appendfsync everysec

 # appendfsync no

 # When the AOF fsync policy is set to always or everysec, and a background

 # saving process (a background save or AOF log background rewriting) is

 # performing a lot of I/O against the disk, in some Linux configurations

 # Redis may block too long on the fsync() call. Note that there is no fix for

 # this currently, as even performing fsync in a different thread will block

 # our synchronous write(2) call.

 #

 # In order to mitigate this problem it's possible to use the following option

 # that will prevent fsync() from being called in the main process while a

 # BGSAVE or BGREWRITEAOF is in progress.

 #

 # This means that while another child is saving, the durability of Redis is

 # the same as "appendfsync none". In practical terms, this means that it is

 # possible to lose up to 30 seconds of log in the worst scenario (with the

 # default Linux settings).

 #

 # If you have latency problems turn this to "yes". Otherwise leave it as

 # "no" that is the safest pick from the point of view of durability.

 no-appendfsync-on-rewrite no

 # Automatic rewrite of the append only file.

 # Redis is able to automatically rewrite the log file implicitly calling

 # BGREWRITEAOF when the AOF log size grows by the specified percentage.

 #

 # This is how it works: Redis remembers the size of the AOF file after the

 # latest rewrite (if no rewrite has happened since the restart, the size of

 # the AOF at startup is used).

 #

 # This base size is compared to the current size. If the current size is

 # bigger than the specified percentage, the rewrite is triggered. Also

 # you need to specify a minimal size for the AOF file to be rewritten, this

 # is useful to avoid rewriting the AOF file even if the percentage increase

 # is reached but it is still pretty small.

 #

 # Specify a percentage of zero in order to disable the automatic AOF

 # rewrite feature.

 auto-aof-rewrite-percentage 100

 auto-aof-rewrite-min-size 64mb

 # An AOF file may be found to be truncated at the end during the Redis

 # startup process, when the AOF data gets loaded back into memory.

 # This may happen when the system where Redis is running

 # crashes, especially when an ext4 filesystem is mounted without the

 # data=ordered option (however this can't happen when Redis itself

 # crashes or aborts but the operating system still works correctly).

 #

 # Redis can either exit with an error when this happens, or load as much

 # data as possible (the default now) and start if the AOF file is found

 # to be truncated at the end. The following option controls this behavior.

 #

 # If aof-load-truncated is set to yes, a truncated AOF file is loaded and

 # the Redis server starts emitting a log to inform the user of the event.

 # Otherwise if the option is set to no, the server aborts with an error

 # and refuses to start. When the option is set to no, the user requires

 # to fix the AOF file using the "redis-check-aof" utility before to restart

 # the server.

 #

 # Note that if the AOF file will be found to be corrupted in the middle

 # the server will still exit with an error. This option only applies when

 # Redis will try to read more data from the AOF file but not enough bytes

 # will be found.

 aof-load-truncated yes

 # When rewriting the AOF file, Redis is able to use an RDB preamble in the

 # AOF file for faster rewrites and recoveries. When this option is turned

 # on the rewritten AOF file is composed of two different stanzas:

 #

 #   [RDB file][AOF tail]

 #

 # When loading Redis recognizes that the AOF file starts with the "REDIS"

 # string and loads the prefixed RDB file, and continues loading the AOF

 # tail.

 #

 # This is currently turned off by default in order to avoid the surprise

 # of a format change, but will at some point be used as the default.

 aof-use-rdb-preamble no

 ################################ LUA SCRIPTING  ###############################

 # Max execution time of a Lua script in milliseconds.

 #

 # If the maximum execution time is reached Redis will log that a script is

 # still in execution after the maximum allowed time and will start to

 # reply to queries with an error.

 #

 # When a long running script exceeds the maximum execution time only the

 # SCRIPT KILL and SHUTDOWN NOSAVE commands are available. The first can be

 # used to stop a script that did not yet called write commands. The second

 # is the only way to shut down the server in the case a write command was

 # already issued by the script but the user doesn't want to wait for the natural

 # termination of the script.

 #

 # Set it to 0 or a negative value for unlimited execution without warnings.

 lua-time-limit 5000

 ################################ REDIS CLUSTER  ###############################

 #

 # ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

 # WARNING EXPERIMENTAL: Redis Cluster is considered to be stable code, however

 # in order to mark it as "mature" we need to wait for a non trivial percentage

 # of users to deploy it in production.

 # ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

 #

 # Normal Redis instances can't be part of a Redis Cluster; only nodes that are

 # started as cluster nodes can. In order to start a Redis instance as a

 # cluster node enable the cluster support uncommenting the following:

 #

 # cluster-enabled yes

 # Every cluster node has a cluster configuration file. This file is not

 # intended to be edited by hand. It is created and updated by Redis nodes.

 # Every Redis Cluster node requires a different cluster configuration file.

 # Make sure that instances running in the same system do not have

 # overlapping cluster configuration file names.

 #

 # cluster-config-file nodes-6379.conf

 # Cluster node timeout is the amount of milliseconds a node must be unreachable

 # for it to be considered in failure state.

 # Most other internal time limits are multiple of the node timeout.

 #

 # cluster-node-timeout 15000

 # A slave of a failing master will avoid to start a failover if its data

 # looks too old.

 #

 # There is no simple way for a slave to actually have an exact measure of

 # its "data age", so the following two checks are performed:

 #

 # 1) If there are multiple slaves able to failover, they exchange messages

 #    in order to try to give an advantage to the slave with the best

 #    replication offset (more data from the master processed).

 #    Slaves will try to get their rank by offset, and apply to the start

 #    of the failover a delay proportional to their rank.

 #

 # 2) Every single slave computes the time of the last interaction with

 #    its master. This can be the last ping or command received (if the master

 #    is still in the "connected" state), or the time that elapsed since the

 #    disconnection with the master (if the replication link is currently down).

 #    If the last interaction is too old, the slave will not try to failover

 #    at all.

 #

 # The point "2" can be tuned by user. Specifically a slave will not perform

 # the failover if, since the last interaction with the master, the time

 # elapsed is greater than:

 #

 #   (node-timeout * slave-validity-factor) + repl-ping-slave-period

 #

 # So for example if node-timeout is 30 seconds, and the slave-validity-factor

 # is 10, and assuming a default repl-ping-slave-period of 10 seconds, the

 # slave will not try to failover if it was not able to talk with the master

 # for longer than 310 seconds.

 #

 # A large slave-validity-factor may allow slaves with too old data to failover

 # a master, while a too small value may prevent the cluster from being able to

 # elect a slave at all.

 #

 # For maximum availability, it is possible to set the slave-validity-factor

 # to a value of 0, which means, that slaves will always try to failover the

 # master regardless of the last time they interacted with the master.

 # (However they'll always try to apply a delay proportional to their

 # offset rank).

 #

 # Zero is the only value able to guarantee that when all the partitions heal

 # the cluster will always be able to continue.

 #

 # cluster-slave-validity-factor 10

 # Cluster slaves are able to migrate to orphaned masters, that are masters

 # that are left without working slaves. This improves the cluster ability

 # to resist to failures as otherwise an orphaned master can't be failed over

 # in case of failure if it has no working slaves.

 #

 # Slaves migrate to orphaned masters only if there are still at least a

 # given number of other working slaves for their old master. This number

 # is the "migration barrier". A migration barrier of 1 means that a slave

 # will migrate only if there is at least 1 other working slave for its master

 # and so forth. It usually reflects the number of slaves you want for every

 # master in your cluster.

 #

 # Default is 1 (slaves migrate only if their masters remain with at least

 # one slave). To disable migration just set it to a very large value.

 # A value of 0 can be set but is useful only for debugging and dangerous

 # in production.

 #

 # cluster-migration-barrier 1

 # By default Redis Cluster nodes stop accepting queries if they detect there

 # is at least an hash slot uncovered (no available node is serving it).

 # This way if the cluster is partially down (for example a range of hash slots

 # are no longer covered) all the cluster becomes, eventually, unavailable.

 # It automatically returns available as soon as all the slots are covered again.

 #

 # However sometimes you want the subset of the cluster which is working,

 # to continue to accept queries for the part of the key space that is still

 # covered. In order to do so, just set the cluster-require-full-coverage

 # option to no.

 #

 # cluster-require-full-coverage yes

 # In order to setup your cluster make sure to read the documentation

 # available at http://redis.io web site.

 ########################## CLUSTER DOCKER/NAT support  ########################

 # In certain deployments, Redis Cluster nodes address discovery fails, because

 # addresses are NAT-ted or because ports are forwarded (the typical case is

 # Docker and other containers).

 #

 # In order to make Redis Cluster working in such environments, a static

 # configuration where each node knows its public address is needed. The

 # following two options are used for this scope, and are:

 #

 # * cluster-announce-ip

 # * cluster-announce-port

 # * cluster-announce-bus-port

 #

 # Each instruct the node about its address, client port, and cluster message

 # bus port. The information is then published in the header of the bus packets

 # so that other nodes will be able to correctly map the address of the node

 # publishing the information.

 #

 # If the above options are not used, the normal Redis Cluster auto-detection

 # will be used instead.

 #

 # Note that when remapped, the bus port may not be at the fixed offset of

 # clients port + 10000, so you can specify any port and bus-port depending

 # on how they get remapped. If the bus-port is not set, a fixed offset of

 # 10000 will be used as usually.

 #

 # Example:

 #

 # cluster-announce-ip 10.1.1.5

 # cluster-announce-port 6379

 # cluster-announce-bus-port 6380

 ################################## SLOW LOG ###################################

 # The Redis Slow Log is a system to log queries that exceeded a specified

 # execution time. The execution time does not include the I/O operations

 # like talking with the client, sending the reply and so forth,

 # but just the time needed to actually execute the command (this is the only

 # stage of command execution where the thread is blocked and can not serve

 # other requests in the meantime).

 #

 # You can configure the slow log with two parameters: one tells Redis

 # what is the execution time, in microseconds, to exceed in order for the

 # command to get logged, and the other parameter is the length of the

 # slow log. When a new command is logged the oldest one is removed from the

 # queue of logged commands.

 # The following time is expressed in microseconds, so 1000000 is equivalent

 # to one second. Note that a negative number disables the slow log, while

 # a value of zero forces the logging of every command.

 slowlog-log-slower-than 10000

 # There is no limit to this length. Just be aware that it will consume memory.

 # You can reclaim memory used by the slow log with SLOWLOG RESET.

 slowlog-max-len 128

 ################################ LATENCY MONITOR ##############################

 # The Redis latency monitoring subsystem samples different operations

 # at runtime in order to collect data related to possible sources of

 # latency of a Redis instance.

 #

 # Via the LATENCY command this information is available to the user that can

 # print graphs and obtain reports.

 #

 # The system only logs operations that were performed in a time equal or

 # greater than the amount of milliseconds specified via the

 # latency-monitor-threshold configuration directive. When its value is set

 # to zero, the latency monitor is turned off.

 #

 # By default latency monitoring is disabled since it is mostly not needed

 # if you don't have latency issues, and collecting data has a performance

 # impact, that while very small, can be measured under big load. Latency

 # monitoring can easily be enabled at runtime using the command

 # "CONFIG SET latency-monitor-threshold <milliseconds>" if needed.

 latency-monitor-threshold 0

 ############################# EVENT NOTIFICATION ##############################

 # Redis can notify Pub/Sub clients about events happening in the key space.

 # This feature is documented at http://redis.io/topics/notifications

 #

 # For instance if keyspace events notification is enabled, and a client

 # performs a DEL operation on key "foo" stored in the Database 0, two

 # messages will be published via Pub/Sub:

 #

 # PUBLISH __keyspace@0__:foo del

 # PUBLISH __keyevent@0__:del foo

 #

 # It is possible to select the events that Redis will notify among a set

 # of classes. Every class is identified by a single character:

 #

 #  K     Keyspace events, published with __keyspace@<db>__ prefix.

 #  E     Keyevent events, published with __keyevent@<db>__ prefix.

 #  g     Generic commands (non-type specific) like DEL, EXPIRE, RENAME, ...

 #  $     String commands

 #  l     List commands

 #  s     Set commands

 #  h     Hash commands

 #  z     Sorted set commands

 #  x     Expired events (events generated every time a key expires)

 #  e     Evicted events (events generated when a key is evicted for maxmemory)

 #  A     Alias for g$lshzxe, so that the "AKE" string means all the events.

 #

 #  The "notify-keyspace-events" takes as argument a string that is composed

 #  of zero or multiple characters. The empty string means that notifications

 #  are disabled.

 #

 #  Example: to enable list and generic events, from the point of view of the

 #           event name, use:

 #

 #  notify-keyspace-events Elg

 #

 #  Example 2: to get the stream of the expired keys subscribing to channel

 #             name __keyevent@0__:expired use:

 #

 #  notify-keyspace-events Ex

 #

 #  By default all notifications are disabled because most users don't need

 #  this feature and the feature has some overhead. Note that if you don't

 #  specify at least one of K or E, no events will be delivered.

 notify-keyspace-events ""

 ############################### ADVANCED CONFIG ###############################

 # Hashes are encoded using a memory efficient data structure when they have a

 # small number of entries, and the biggest entry does not exceed a given

 # threshold. These thresholds can be configured using the following directives.

 hash-max-ziplist-entries 512

 hash-max-ziplist-value 64

 # Lists are also encoded in a special way to save a lot of space.

 # The number of entries allowed per internal list node can be specified

 # as a fixed maximum size or a maximum number of elements.

 # For a fixed maximum size, use -5 through -1, meaning:

 # -5: max size: 64 Kb  <-- not recommended for normal workloads

 # -4: max size: 32 Kb  <-- not recommended

 # -3: max size: 16 Kb  <-- probably not recommended

 # -2: max size: 8 Kb   <-- good

 # -1: max size: 4 Kb   <-- good

 # Positive numbers mean store up to _exactly_ that number of elements

 # per list node.

 # The highest performing option is usually -2 (8 Kb size) or -1 (4 Kb size),

 # but if your use case is unique, adjust the settings as necessary.

 list-max-ziplist-size -2

 # Lists may also be compressed.

 # Compress depth is the number of quicklist ziplist nodes from *each* side of

 # the list to *exclude* from compression.  The head and tail of the list

 # are always uncompressed for fast push/pop operations.  Settings are:

 # 0: disable all list compression

 # 1: depth 1 means "don't start compressing until after 1 node into the list,

 #    going from either the head or tail"

 #    So: [head]->node->node->...->node->[tail]

 #    [head], [tail] will always be uncompressed; inner nodes will compress.

 # 2: [head]->[next]->node->node->...->node->[prev]->[tail]

 #    2 here means: don't compress head or head->next or tail->prev or tail,

 #    but compress all nodes between them.

 # 3: [head]->[next]->[next]->node->node->...->node->[prev]->[prev]->[tail]

 # etc.

 list-compress-depth 0

 # Sets have a special encoding in just one case: when a set is composed

 # of just strings that happen to be integers in radix 10 in the range

 # of 64 bit signed integers.

 # The following configuration setting sets the limit in the size of the

 # set in order to use this special memory saving encoding.

 set-max-intset-entries 512

 # Similarly to hashes and lists, sorted sets are also specially encoded in

 # order to save a lot of space. This encoding is only used when the length and

 # elements of a sorted set are below the following limits:

 zset-max-ziplist-entries 128

 zset-max-ziplist-value 64

 # HyperLogLog sparse representation bytes limit. The limit includes the

 # 16 bytes header. When an HyperLogLog using the sparse representation crosses

 # this limit, it is converted into the dense representation.

 #

 # A value greater than 16000 is totally useless, since at that point the

 # dense representation is more memory efficient.

 #

 # The suggested value is ~ 3000 in order to have the benefits of

 # the space efficient encoding without slowing down too much PFADD,

 # which is O(N) with the sparse encoding. The value can be raised to

 # ~ 10000 when CPU is not a concern, but space is, and the data set is

 # composed of many HyperLogLogs with cardinality in the 0 - 15000 range.

 hll-sparse-max-bytes 3000

 # Active rehashing uses 1 millisecond every 100 milliseconds of CPU time in

 # order to help rehashing the main Redis hash table (the one mapping top-level

 # keys to values). The hash table implementation Redis uses (see dict.c)

 # performs a lazy rehashing: the more operation you run into a hash table

 # that is rehashing, the more rehashing "steps" are performed, so if the

 # server is idle the rehashing is never complete and some more memory is used

 # by the hash table.

 #

 # The default is to use this millisecond 10 times every second in order to

 # actively rehash the main dictionaries, freeing memory when possible.

 #

 # If unsure:

 # use "activerehashing no" if you have hard latency requirements and it is

 # not a good thing in your environment that Redis can reply from time to time

 # to queries with 2 milliseconds delay.

 #

 # use "activerehashing yes" if you don't have such hard requirements but

 # want to free memory asap when possible.

 activerehashing yes

 # The client output buffer limits can be used to force disconnection of clients

 # that are not reading data from the server fast enough for some reason (a

 # common reason is that a Pub/Sub client can't consume messages as fast as the

 # publisher can produce them).

 #

 # The limit can be set differently for the three different classes of clients:

 #

 # normal -> normal clients including MONITOR clients

 # slave  -> slave clients

 # pubsub -> clients subscribed to at least one pubsub channel or pattern

 #

 # The syntax of every client-output-buffer-limit directive is the following:

 #

 # client-output-buffer-limit <class> <hard limit> <soft limit> <soft seconds>

 #

 # A client is immediately disconnected once the hard limit is reached, or if

 # the soft limit is reached and remains reached for the specified number of

 # seconds (continuously).

 # So for instance if the hard limit is 32 megabytes and the soft limit is

 # 16 megabytes / 10 seconds, the client will get disconnected immediately

 # if the size of the output buffers reach 32 megabytes, but will also get

 # disconnected if the client reaches 16 megabytes and continuously overcomes

 # the limit for 10 seconds.

 #

 # By default normal clients are not limited because they don't receive data

 # without asking (in a push way), but just after a request, so only

 # asynchronous clients may create a scenario where data is requested faster

 # than it can read.

 #

 # Instead there is a default limit for pubsub and slave clients, since

 # subscribers and slaves receive data in a push fashion.

 #

 # Both the hard or the soft limit can be disabled by setting them to zero.

 client-output-buffer-limit normal 0 0 0

 client-output-buffer-limit slave 256mb 64mb 60

 client-output-buffer-limit pubsub 32mb 8mb 60

 # Client query buffers accumulate new commands. They are limited to a fixed

 # amount by default in order to avoid that a protocol desynchronization (for

 # instance due to a bug in the client) will lead to unbound memory usage in

 # the query buffer. However you can configure it here if you have very special

 # needs, such us huge multi/exec requests or alike.

 #

 # client-query-buffer-limit 1gb

 # In the Redis protocol, bulk requests, that are, elements representing single

 # strings, are normally limited ot 512 mb. However you can change this limit

 # here.

 #

 # proto-max-bulk-len 512mb

 # Redis calls an internal function to perform many background tasks, like

 # closing connections of clients in timeout, purging expired keys that are

 # never requested, and so forth.

 #

 # Not all tasks are performed with the same frequency, but Redis checks for

 # tasks to perform according to the specified "hz" value.

 #

 # By default "hz" is set to 10. Raising the value will use more CPU when

 # Redis is idle, but at the same time will make Redis more responsive when

 # there are many keys expiring at the same time, and timeouts may be

 # handled with more precision.

 #

 # The range is between 1 and 500, however a value over 100 is usually not

 # a good idea. Most users should use the default of 10 and raise this up to

 # 100 only in environments where very low latency is required.

 hz 10

 # When a child rewrites the AOF file, if the following option is enabled

 # the file will be fsync-ed every 32 MB of data generated. This is useful

 # in order to commit the file to the disk more incrementally and avoid

 # big latency spikes.

 aof-rewrite-incremental-fsync yes

 # Redis LFU eviction (see maxmemory setting) can be tuned. However it is a good

 # idea to start with the default settings and only change them after investigating

 # how to improve the performances and how the keys LFU change over time, which

 # is possible to inspect via the OBJECT FREQ command.

 #

 # There are two tunable parameters in the Redis LFU implementation: the

 # counter logarithm factor and the counter decay time. It is important to

 # understand what the two parameters mean before changing them.

 #

 # The LFU counter is just 8 bits per key, it's maximum value is 255, so Redis

 # uses a probabilistic increment with logarithmic behavior. Given the value

 # of the old counter, when a key is accessed, the counter is incremented in

 # this way:

 #

 # 1. A random number R between 0 and 1 is extracted.

 # 2. A probability P is calculated as 1/(old_value*lfu_log_factor+1).

 # 3. The counter is incremented only if R < P.

 #

 # The default lfu-log-factor is 10. This is a table of how the frequency

 # counter changes with a different number of accesses with different

 # logarithmic factors:

 #

 # +--------+------------+------------+------------+------------+------------+

 # | factor | 100 hits   | 1000 hits  | 100K hits  | 1M hits    | 10M hits   |

 # +--------+------------+------------+------------+------------+------------+

 # | 0      | 104        | 255        | 255        | 255        | 255        |

 # +--------+------------+------------+------------+------------+------------+

 # | 1      | 18         | 49         | 255        | 255        | 255        |

 # +--------+------------+------------+------------+------------+------------+

 # | 10     | 10         | 18         | 142        | 255        | 255        |

 # +--------+------------+------------+------------+------------+------------+

 # | 100    | 8          | 11         | 49         | 143        | 255        |

 # +--------+------------+------------+------------+------------+------------+

 #

 # NOTE: The above table was obtained by running the following commands:

 #

 #   redis-benchmark -n 1000000 incr foo

 #   redis-cli object freq foo

 #

 # NOTE 2: The counter initial value is 5 in order to give new objects a chance

 # to accumulate hits.

 #

 # The counter decay time is the time, in minutes, that must elapse in order

 # for the key counter to be divided by two (or decremented if it has a value

 # less <= 10).

 #

 # The default value for the lfu-decay-time is 1. A Special value of 0 means to

 # decay the counter every time it happens to be scanned.

 #

 # lfu-log-factor 10

 # lfu-decay-time 1

 ########################### ACTIVE DEFRAGMENTATION #######################

 #

 # WARNING THIS FEATURE IS EXPERIMENTAL. However it was stress tested

 # even in production and manually tested by multiple engineers for some

 # time.

 #

 # What is active defragmentation?

 # -------------------------------

 #

 # Active (online) defragmentation allows a Redis server to compact the

 # spaces left between small allocations and deallocations of data in memory,

 # thus allowing to reclaim back memory.

 #

 # Fragmentation is a natural process that happens with every allocator (but

 # less so with Jemalloc, fortunately) and certain workloads. Normally a server

 # restart is needed in order to lower the fragmentation, or at least to flush

 # away all the data and create it again. However thanks to this feature

 # implemented by Oran Agra for Redis 4.0 this process can happen at runtime

 # in an "hot" way, while the server is running.

 #

 # Basically when the fragmentation is over a certain level (see the

 # configuration options below) Redis will start to create new copies of the

 # values in contiguous memory regions by exploiting certain specific Jemalloc

 # features (in order to understand if an allocation is causing fragmentation

 # and to allocate it in a better place), and at the same time, will release the

 # old copies of the data. This process, repeated incrementally for all the keys

 # will cause the fragmentation to drop back to normal values.

 #

 # Important things to understand:

 #

 # 1. This feature is disabled by default, and only works if you compiled Redis

 #    to use the copy of Jemalloc we ship with the source code of Redis.

 #    This is the default with Linux builds.

 #

 # 2. You never need to enable this feature if you don't have fragmentation

 #    issues.

 #

 # 3. Once you experience fragmentation, you can enable this feature when

 #    needed with the command "CONFIG SET activedefrag yes".

 #

 # The configuration parameters are able to fine tune the behavior of the

 # defragmentation process. If you are not sure about what they mean it is

 # a good idea to leave the defaults untouched.

 # Enabled active defragmentation

 # activedefrag yes

 # Minimum amount of fragmentation waste to start active defrag

 # active-defrag-ignore-bytes 100mb

 # Minimum percentage of fragmentation to start active defrag

 # active-defrag-threshold-lower 10

 # Maximum percentage of fragmentation at which we use maximum effort

 # active-defrag-threshold-upper 100

 # Minimal effort for defrag in CPU percentage

 # active-defrag-cycle-min 25

 # Maximal effort for defrag in CPU percentage

 # active-defrag-cycle-max 75

3.2、从数据库redis6380.conf的配置如下

 # Redis configuration file example.

 #

 # Note that in order to read the configuration file, Redis must be

 # started with the file path as first argument:

 #

 # ./redis-server /path/to/redis.conf

 # Note on units: when memory size is needed, it is possible to specify

 # it in the usual form of 1k 5GB 4M and so forth:

 #

 # 1k => 1000 bytes

 # 1kb => 1024 bytes

 # 1m => 1000000 bytes

 # 1mb => 1024*1024 bytes

 # 1g => 1000000000 bytes

 # 1gb => 1024*1024*1024 bytes

 #

 # units are case insensitive so 1GB 1Gb 1gB are all the same.

 ################################## INCLUDES ###################################

 # Include one or more other config files here.  This is useful if you

 # have a standard template that goes to all Redis servers but also need

 # to customize a few per-server settings.  Include files can include

 # other files, so use this wisely.

 #

 # Notice option "include" won't be rewritten by command "CONFIG REWRITE"

 # from admin or Redis Sentinel. Since Redis always uses the last processed

 # line as value of a configuration directive, you'd better put includes

 # at the beginning of this file to avoid overwriting config change at runtime.

 #

 # If instead you are interested in using includes to override configuration

 # options, it is better to use include as the last line.

 #

 # include /path/to/local.conf

 # include /path/to/other.conf

 ################################## MODULES #####################################

 # Load modules at startup. If the server is not able to load modules

 # it will abort. It is possible to use multiple loadmodule directives.

 #

 # loadmodule /path/to/my_module.so

 # loadmodule /path/to/other_module.so

 ################################## NETWORK #####################################

 # By default, if no "bind" configuration directive is specified, Redis listens

 # for connections from all the network interfaces available on the server.

 # It is possible to listen to just one or multiple selected interfaces using

 # the "bind" configuration directive, followed by one or more IP addresses.

 #

 # Examples:

 #

 # bind 192.168.1.100 10.0.0.1

 # bind 127.0.0.1 ::1

 #

 # ~~~ WARNING ~~~ If the computer running Redis is directly exposed to the

 # internet, binding to all the interfaces is dangerous and will expose the

 # instance to everybody on the internet. So by default we uncomment the

 # following bind directive, that will force Redis to listen only into

 # the IPv4 lookback interface address (this means Redis will be able to

 # accept connections only from clients running into the same computer it

 # is running).

 #

 # IF YOU ARE SURE YOU WANT YOUR INSTANCE TO LISTEN TO ALL THE INTERFACES

 # JUST COMMENT THE FOLLOWING LINE.

 # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 bind 127.0.0.1

 # Protected mode is a layer of security protection, in order to avoid that

 # Redis instances left open on the internet are accessed and exploited.

 #

 # When protected mode is on and if:

 #

 # 1) The server is not binding explicitly to a set of addresses using the

 #    "bind" directive.

 # 2) No password is configured.

 #

 # The server only accepts connections from clients connecting from the

 # IPv4 and IPv6 loopback addresses 127.0.0.1 and ::1, and from Unix domain

 # sockets.

 #

 # By default protected mode is enabled. You should disable it only if

 # you are sure you want clients from other hosts to connect to Redis

 # even if no authentication is configured, nor a specific set of interfaces

 # are explicitly listed using the "bind" directive.

 protected-mode yes

 # Accept connections on the specified port, default is 6379 (IANA #815344).

 # If port 0 is specified Redis will not listen on a TCP socket.

 port 6380

 # TCP listen() backlog.

 #

 # In high requests-per-second environments you need an high backlog in order

 # to avoid slow clients connections issues. Note that the Linux kernel

 # will silently truncate it to the value of /proc/sys/net/core/somaxconn so

 # make sure to raise both the value of somaxconn and tcp_max_syn_backlog

 # in order to get the desired effect.

 tcp-backlog 511

 # Unix socket.

 #

 # Specify the path for the Unix socket that will be used to listen for

 # incoming connections. There is no default, so Redis will not listen

 # on a unix socket when not specified.

 #

 # unixsocket /tmp/redis.sock

 # unixsocketperm 700

 # Close the connection after a client is idle for N seconds (0 to disable)

 timeout 0

 # TCP keepalive.

 #

 # If non-zero, use SO_KEEPALIVE to send TCP ACKs to clients in absence

 # of communication. This is useful for two reasons:

 #

 # 1) Detect dead peers.

 # 2) Take the connection alive from the point of view of network

 #    equipment in the middle.

 #

 # On Linux, the specified value (in seconds) is the period used to send ACKs.

 # Note that to close the connection the double of the time is needed.

 # On other kernels the period depends on the kernel configuration.

 #

 # A reasonable value for this option is 300 seconds, which is the new

 # Redis default starting with Redis 3.2.1.

 tcp-keepalive 300

 ################################# GENERAL #####################################

 # By default Redis does not run as a daemon. Use 'yes' if you need it.

 # Note that Redis will write a pid file in /var/run/redis.pid when daemonized.

 daemonize yes

 # If you run Redis from upstart or systemd, Redis can interact with your

 # supervision tree. Options:

 #   supervised no      - no supervision interaction

 #   supervised upstart - signal upstart by putting Redis into SIGSTOP mode

 #   supervised systemd - signal systemd by writing READY=1 to $NOTIFY_SOCKET

 #   supervised auto    - detect upstart or systemd method based on

 #                        UPSTART_JOB or NOTIFY_SOCKET environment variables

 # Note: these supervision methods only signal "process is ready."

 #       They do not enable continuous liveness pings back to your supervisor.

 supervised no

 # If a pid file is specified, Redis writes it where specified at startup

 # and removes it at exit.

 #

 # When the server runs non daemonized, no pid file is created if none is

 # specified in the configuration. When the server is daemonized, the pid file

 # is used even if not specified, defaulting to "/var/run/redis.pid".

 #

 # Creating a pid file is best effort: if Redis is not able to create it

 # nothing bad happens, the server will start and run normally.

 pidfile /var/run/redis_6380.pid

 # Specify the server verbosity level.

 # This can be one of:

 # debug (a lot of information, useful for development/testing)

 # verbose (many rarely useful info, but not a mess like the debug level)

 # notice (moderately verbose, what you want in production probably)

 # warning (only very important / critical messages are logged)

 loglevel notice

 # Specify the log file name. Also the empty string can be used to force

 # Redis to log on the standard output. Note that if you use standard

 # output for logging but daemonize, logs will be sent to /dev/null

 logfile "redis_6380.log"

 # To enable logging to the system logger, just set 'syslog-enabled' to yes,

 # and optionally update the other syslog parameters to suit your needs.

 # syslog-enabled no

 # Specify the syslog identity.

 # syslog-ident redis

 # Specify the syslog facility. Must be USER or between LOCAL0-LOCAL7.

 # syslog-facility local0

 # Set the number of databases. The default database is DB 0, you can select

 # a different one on a per-connection basis using SELECT <dbid> where

 # dbid is a number between 0 and 'databases'-1

 databases 16

 # By default Redis shows an ASCII art logo only when started to log to the

 # standard output and if the standard output is a TTY. Basically this means

 # that normally a logo is displayed only in interactive sessions.

 #

 # However it is possible to force the pre-4.0 behavior and always show a

 # ASCII art logo in startup logs by setting the following option to yes.

 always-show-logo yes

 ################################ SNAPSHOTTING  ################################

 #

 # Save the DB on disk:

 #

 #   save <seconds> <changes>

 #

 #   Will save the DB if both the given number of seconds and the given

 #   number of write operations against the DB occurred.

 #

 #   In the example below the behaviour will be to save:

 #   after 900 sec (15 min) if at least 1 key changed

 #   after 300 sec (5 min) if at least 10 keys changed

 #   after 60 sec if at least 10000 keys changed

 #

 #   Note: you can disable saving completely by commenting out all "save" lines.

 #

 #   It is also possible to remove all the previously configured save

 #   points by adding a save directive with a single empty string argument

 #   like in the following example:

 #

 #   save ""

 save 900 1

 save 300 10

 save 60 10000

 # By default Redis will stop accepting writes if RDB snapshots are enabled

 # (at least one save point) and the latest background save failed.

 # This will make the user aware (in a hard way) that data is not persisting

 # on disk properly, otherwise chances are that no one will notice and some

 # disaster will happen.

 #

 # If the background saving process will start working again Redis will

 # automatically allow writes again.

 #

 # However if you have setup your proper monitoring of the Redis server

 # and persistence, you may want to disable this feature so that Redis will

 # continue to work as usual even if there are problems with disk,

 # permissions, and so forth.

 stop-writes-on-bgsave-error yes

 # Compress string objects using LZF when dump .rdb databases?

 # For default that's set to 'yes' as it's almost always a win.

 # If you want to save some CPU in the saving child set it to 'no' but

 # the dataset will likely be bigger if you have compressible values or keys.

 rdbcompression yes

 # Since version 5 of RDB a CRC64 checksum is placed at the end of the file.

 # This makes the format more resistant to corruption but there is a performance

 # hit to pay (around 10%) when saving and loading RDB files, so you can disable it

 # for maximum performances.

 #

 # RDB files created with checksum disabled have a checksum of zero that will

 # tell the loading code to skip the check.

 rdbchecksum yes

 # The filename where to dump the DB

 dbfilename dump_6380.rdb

 # The working directory.

 #

 # The DB will be written inside this directory, with the filename specified

 # above using the 'dbfilename' configuration directive.

 #

 # The Append Only File will also be created inside this directory.

 #

 # Note that you must specify a directory here, not a file name.

 dir ./

 ################################# REPLICATION #################################

 # Master-Slave replication. Use slaveof to make a Redis instance a copy of

 # another Redis server. A few things to understand ASAP about Redis replication.

 #

 # 1) Redis replication is asynchronous, but you can configure a master to

 #    stop accepting writes if it appears to be not connected with at least

 #    a given number of slaves.

 # 2) Redis slaves are able to perform a partial resynchronization with the

 #    master if the replication link is lost for a relatively small amount of

 #    time. You may want to configure the replication backlog size (see the next

 #    sections of this file) with a sensible value depending on your needs.

 # 3) Replication is automatic and does not need user intervention. After a

 #    network partition slaves automatically try to reconnect to masters

 #    and resynchronize with them.

 #

 slaveof 127.0.0.1 6379

 # If the master is password protected (using the "requirepass" configuration

 # directive below) it is possible to tell the slave to authenticate before

 # starting the replication synchronization process, otherwise the master will

 # refuse the slave request.

 #

 # masterauth <master-password>

 # When a slave loses its connection with the master, or when the replication

 # is still in progress, the slave can act in two different ways:

 #

 # 1) if slave-serve-stale-data is set to 'yes' (the default) the slave will

 #    still reply to client requests, possibly with out of date data, or the

 #    data set may just be empty if this is the first synchronization.

 #

 # 2) if slave-serve-stale-data is set to 'no' the slave will reply with

 #    an error "SYNC with master in progress" to all the kind of commands

 #    but to INFO and SLAVEOF.

 #

 slave-serve-stale-data yes

 # You can configure a slave instance to accept writes or not. Writing against

 # a slave instance may be useful to store some ephemeral data (because data

 # written on a slave will be easily deleted after resync with the master) but

 # may also cause problems if clients are writing to it because of a

 # misconfiguration.

 #

 # Since Redis 2.6 by default slaves are read-only.

 #

 # Note: read only slaves are not designed to be exposed to untrusted clients

 # on the internet. It's just a protection layer against misuse of the instance.

 # Still a read only slave exports by default all the administrative commands

 # such as CONFIG, DEBUG, and so forth. To a limited extent you can improve

 # security of read only slaves using 'rename-command' to shadow all the

 # administrative / dangerous commands.

 slave-read-only yes

 # Replication SYNC strategy: disk or socket.

 #

 # -------------------------------------------------------

 # WARNING: DISKLESS REPLICATION IS EXPERIMENTAL CURRENTLY

 # -------------------------------------------------------

 #

 # New slaves and reconnecting slaves that are not able to continue the replication

 # process just receiving differences, need to do what is called a "full

 # synchronization". An RDB file is transmitted from the master to the slaves.

 # The transmission can happen in two different ways:

 #

 # 1) Disk-backed: The Redis master creates a new process that writes the RDB

 #                 file on disk. Later the file is transferred by the parent

 #                 process to the slaves incrementally.

 # 2) Diskless: The Redis master creates a new process that directly writes the

 #              RDB file to slave sockets, without touching the disk at all.

 #

 # With disk-backed replication, while the RDB file is generated, more slaves

 # can be queued and served with the RDB file as soon as the current child producing

 # the RDB file finishes its work. With diskless replication instead once

 # the transfer starts, new slaves arriving will be queued and a new transfer

 # will start when the current one terminates.

 #

 # When diskless replication is used, the master waits a configurable amount of

 # time (in seconds) before starting the transfer in the hope that multiple slaves

 # will arrive and the transfer can be parallelized.

 #

 # With slow disks and fast (large bandwidth) networks, diskless replication

 # works better.

 repl-diskless-sync no

 # When diskless replication is enabled, it is possible to configure the delay

 # the server waits in order to spawn the child that transfers the RDB via socket

 # to the slaves.

 #

 # This is important since once the transfer starts, it is not possible to serve

 # new slaves arriving, that will be queued for the next RDB transfer, so the server

 # waits a delay in order to let more slaves arrive.

 #

 # The delay is specified in seconds, and by default is 5 seconds. To disable

 # it entirely just set it to 0 seconds and the transfer will start ASAP.

 repl-diskless-sync-delay 5

 # Slaves send PINGs to server in a predefined interval. It's possible to change

 # this interval with the repl_ping_slave_period option. The default value is 10

 # seconds.

 #

 # repl-ping-slave-period 10

 # The following option sets the replication timeout for:

 #

 # 1) Bulk transfer I/O during SYNC, from the point of view of slave.

 # 2) Master timeout from the point of view of slaves (data, pings).

 # 3) Slave timeout from the point of view of masters (REPLCONF ACK pings).

 #

 # It is important to make sure that this value is greater than the value

 # specified for repl-ping-slave-period otherwise a timeout will be detected

 # every time there is low traffic between the master and the slave.

 #

 # repl-timeout 60

 # Disable TCP_NODELAY on the slave socket after SYNC?

 #

 # If you select "yes" Redis will use a smaller number of TCP packets and

 # less bandwidth to send data to slaves. But this can add a delay for

 # the data to appear on the slave side, up to 40 milliseconds with

 # Linux kernels using a default configuration.

 #

 # If you select "no" the delay for data to appear on the slave side will

 # be reduced but more bandwidth will be used for replication.

 #

 # By default we optimize for low latency, but in very high traffic conditions

 # or when the master and slaves are many hops away, turning this to "yes" may

 # be a good idea.

 repl-disable-tcp-nodelay no

 # Set the replication backlog size. The backlog is a buffer that accumulates

 # slave data when slaves are disconnected for some time, so that when a slave

 # wants to reconnect again, often a full resync is not needed, but a partial

 # resync is enough, just passing the portion of data the slave missed while

 # disconnected.

 #

 # The bigger the replication backlog, the longer the time the slave can be

 # disconnected and later be able to perform a partial resynchronization.

 #

 # The backlog is only allocated once there is at least a slave connected.

 #

 # repl-backlog-size 1mb

 # After a master has no longer connected slaves for some time, the backlog

 # will be freed. The following option configures the amount of seconds that

 # need to elapse, starting from the time the last slave disconnected, for

 # the backlog buffer to be freed.

 #

 # Note that slaves never free the backlog for timeout, since they may be

 # promoted to masters later, and should be able to correctly "partially

 # resynchronize" with the slaves: hence they should always accumulate backlog.

 #

 # A value of 0 means to never release the backlog.

 #

 # repl-backlog-ttl 3600

 # The slave priority is an integer number published by Redis in the INFO output.

 # It is used by Redis Sentinel in order to select a slave to promote into a

 # master if the master is no longer working correctly.

 #

 # A slave with a low priority number is considered better for promotion, so

 # for instance if there are three slaves with priority 10, 100, 25 Sentinel will

 # pick the one with priority 10, that is the lowest.

 #

 # However a special priority of 0 marks the slave as not able to perform the

 # role of master, so a slave with priority of 0 will never be selected by

 # Redis Sentinel for promotion.

 #

 # By default the priority is 100.

 slave-priority 100

 # It is possible for a master to stop accepting writes if there are less than

 # N slaves connected, having a lag less or equal than M seconds.

 #

 # The N slaves need to be in "online" state.

 #

 # The lag in seconds, that must be <= the specified value, is calculated from

 # the last ping received from the slave, that is usually sent every second.

 #

 # This option does not GUARANTEE that N replicas will accept the write, but

 # will limit the window of exposure for lost writes in case not enough slaves

 # are available, to the specified number of seconds.

 #

 # For example to require at least 3 slaves with a lag <= 10 seconds use:

 #

 # min-slaves-to-write 3

 # min-slaves-max-lag 10

 #

 # Setting one or the other to 0 disables the feature.

 #

 # By default min-slaves-to-write is set to 0 (feature disabled) and

 # min-slaves-max-lag is set to 10.

 # A Redis master is able to list the address and port of the attached

 # slaves in different ways. For example the "INFO replication" section

 # offers this information, which is used, among other tools, by

 # Redis Sentinel in order to discover slave instances.

 # Another place where this info is available is in the output of the

 # "ROLE" command of a master.

 #

 # The listed IP and address normally reported by a slave is obtained

 # in the following way:

 #

 #   IP: The address is auto detected by checking the peer address

 #   of the socket used by the slave to connect with the master.

 #

 #   Port: The port is communicated by the slave during the replication

 #   handshake, and is normally the port that the slave is using to

 #   list for connections.

 #

 # However when port forwarding or Network Address Translation (NAT) is

 # used, the slave may be actually reachable via different IP and port

 # pairs. The following two options can be used by a slave in order to

 # report to its master a specific set of IP and port, so that both INFO

 # and ROLE will report those values.

 #

 # There is no need to use both the options if you need to override just

 # the port or the IP address.

 #

 # slave-announce-ip 5.5.5.5

 # slave-announce-port 1234

 ################################## SECURITY ###################################

 # Require clients to issue AUTH <PASSWORD> before processing any other

 # commands.  This might be useful in environments in which you do not trust

 # others with access to the host running redis-server.

 #

 # This should stay commented out for backward compatibility and because most

 # people do not need auth (e.g. they run their own servers).

 #

 # Warning: since Redis is pretty fast an outside user can try up to

 # 150k passwords per second against a good box. This means that you should

 # use a very strong password otherwise it will be very easy to break.

 #

 # requirepass foobared

 # Command renaming.

 #

 # It is possible to change the name of dangerous commands in a shared

 # environment. For instance the CONFIG command may be renamed into something

 # hard to guess so that it will still be available for internal-use tools

 # but not available for general clients.

 #

 # Example:

 #

 # rename-command CONFIG b840fc02d524045429941cc15f59e41cb7be6c52

 #

 # It is also possible to completely kill a command by renaming it into

 # an empty string:

 #

 # rename-command CONFIG ""

 #

 # Please note that changing the name of commands that are logged into the

 # AOF file or transmitted to slaves may cause problems.

 ################################### CLIENTS ####################################

 # Set the max number of connected clients at the same time. By default

 # this limit is set to 10000 clients, however if the Redis server is not

 # able to configure the process file limit to allow for the specified limit

 # the max number of allowed clients is set to the current file limit

 # minus 32 (as Redis reserves a few file descriptors for internal uses).

 #

 # Once the limit is reached Redis will close all the new connections sending

 # an error 'max number of clients reached'.

 #

 # maxclients 10000

 ############################## MEMORY MANAGEMENT ################################

 # Set a memory usage limit to the specified amount of bytes.

 # When the memory limit is reached Redis will try to remove keys

 # according to the eviction policy selected (see maxmemory-policy).

 #

 # If Redis can't remove keys according to the policy, or if the policy is

 # set to 'noeviction', Redis will start to reply with errors to commands

 # that would use more memory, like SET, LPUSH, and so on, and will continue

 # to reply to read-only commands like GET.

 #

 # This option is usually useful when using Redis as an LRU or LFU cache, or to

 # set a hard memory limit for an instance (using the 'noeviction' policy).

 #

 # WARNING: If you have slaves attached to an instance with maxmemory on,

 # the size of the output buffers needed to feed the slaves are subtracted

 # from the used memory count, so that network problems / resyncs will

 # not trigger a loop where keys are evicted, and in turn the output

 # buffer of slaves is full with DELs of keys evicted triggering the deletion

 # of more keys, and so forth until the database is completely emptied.

 #

 # In short... if you have slaves attached it is suggested that you set a lower

 # limit for maxmemory so that there is some free RAM on the system for slave

 # output buffers (but this is not needed if the policy is 'noeviction').

 #

 # maxmemory <bytes>

 # MAXMEMORY POLICY: how Redis will select what to remove when maxmemory

 # is reached. You can select among five behaviors:

 #

 # volatile-lru -> Evict using approximated LRU among the keys with an expire set.

 # allkeys-lru -> Evict any key using approximated LRU.

 # volatile-lfu -> Evict using approximated LFU among the keys with an expire set.

 # allkeys-lfu -> Evict any key using approximated LFU.

 # volatile-random -> Remove a random key among the ones with an expire set.

 # allkeys-random -> Remove a random key, any key.

 # volatile-ttl -> Remove the key with the nearest expire time (minor TTL)

 # noeviction -> Don't evict anything, just return an error on write operations.

 #

 # LRU means Least Recently Used

 # LFU means Least Frequently Used

 #

 # Both LRU, LFU and volatile-ttl are implemented using approximated

 # randomized algorithms.

 #

 # Note: with any of the above policies, Redis will return an error on write

 #       operations, when there are no suitable keys for eviction.

 #

 #       At the date of writing these commands are: set setnx setex append

 #       incr decr rpush lpush rpushx lpushx linsert lset rpoplpush sadd

 #       sinter sinterstore sunion sunionstore sdiff sdiffstore zadd zincrby

 #       zunionstore zinterstore hset hsetnx hmset hincrby incrby decrby

 #       getset mset msetnx exec sort

 #

 # The default is:

 #

 # maxmemory-policy noeviction

 # LRU, LFU and minimal TTL algorithms are not precise algorithms but approximated

 # algorithms (in order to save memory), so you can tune it for speed or

 # accuracy. For default Redis will check five keys and pick the one that was

 # used less recently, you can change the sample size using the following

 # configuration directive.

 #

 # The default of 5 produces good enough results. 10 Approximates very closely

 # true LRU but costs more CPU. 3 is faster but not very accurate.

 #

 # maxmemory-samples 5

 ############################# LAZY FREEING ####################################

 # Redis has two primitives to delete keys. One is called DEL and is a blocking

 # deletion of the object. It means that the server stops processing new commands

 # in order to reclaim all the memory associated with an object in a synchronous

 # way. If the key deleted is associated with a small object, the time needed

 # in order to execute the DEL command is very small and comparable to most other

 # O(1) or O(log_N) commands in Redis. However if the key is associated with an

 # aggregated value containing millions of elements, the server can block for

 # a long time (even seconds) in order to complete the operation.

 #

 # For the above reasons Redis also offers non blocking deletion primitives

 # such as UNLINK (non blocking DEL) and the ASYNC option of FLUSHALL and

 # FLUSHDB commands, in order to reclaim memory in background. Those commands

 # are executed in constant time. Another thread will incrementally free the

 # object in the background as fast as possible.

 #

 # DEL, UNLINK and ASYNC option of FLUSHALL and FLUSHDB are user-controlled.

 # It's up to the design of the application to understand when it is a good

 # idea to use one or the other. However the Redis server sometimes has to

 # delete keys or flush the whole database as a side effect of other operations.

 # Specifically Redis deletes objects independently of a user call in the

 # following scenarios:

 #

 # 1) On eviction, because of the maxmemory and maxmemory policy configurations,

 #    in order to make room for new data, without going over the specified

 #    memory limit.

 # 2) Because of expire: when a key with an associated time to live (see the

 #    EXPIRE command) must be deleted from memory.

 # 3) Because of a side effect of a command that stores data on a key that may

 #    already exist. For example the RENAME command may delete the old key

 #    content when it is replaced with another one. Similarly SUNIONSTORE

 #    or SORT with STORE option may delete existing keys. The SET command

 #    itself removes any old content of the specified key in order to replace

 #    it with the specified string.

 # 4) During replication, when a slave performs a full resynchronization with

 #    its master, the content of the whole database is removed in order to

 #    load the RDB file just transfered.

 #

 # In all the above cases the default is to delete objects in a blocking way,

 # like if DEL was called. However you can configure each case specifically

 # in order to instead release memory in a non-blocking way like if UNLINK

 # was called, using the following configuration directives:

 lazyfree-lazy-eviction no

 lazyfree-lazy-expire no

 lazyfree-lazy-server-del no

 slave-lazy-flush no

 ############################## APPEND ONLY MODE ###############################

 # By default Redis asynchronously dumps the dataset on disk. This mode is

 # good enough in many applications, but an issue with the Redis process or

 # a power outage may result into a few minutes of writes lost (depending on

 # the configured save points).

 #

 # The Append Only File is an alternative persistence mode that provides

 # much better durability. For instance using the default data fsync policy

 # (see later in the config file) Redis can lose just one second of writes in a

 # dramatic event like a server power outage, or a single write if something

 # wrong with the Redis process itself happens, but the operating system is

 # still running correctly.

 #

 # AOF and RDB persistence can be enabled at the same time without problems.

 # If the AOF is enabled on startup Redis will load the AOF, that is the file

 # with the better durability guarantees.

 #

 # Please check http://redis.io/topics/persistence for more information.

 appendonly no

 # The name of the append only file (default: "appendonly.aof")

 appendfilename "appendonly6380.aof"

 # The fsync() call tells the Operating System to actually write data on disk

 # instead of waiting for more data in the output buffer. Some OS will really flush

 # data on disk, some other OS will just try to do it ASAP.

 #

 # Redis supports three different modes:

 #

 # no: don't fsync, just let the OS flush the data when it wants. Faster.

 # always: fsync after every write to the append only log. Slow, Safest.

 # everysec: fsync only one time every second. Compromise.

 #

 # The default is "everysec", as that's usually the right compromise between

 # speed and data safety. It's up to you to understand if you can relax this to

 # "no" that will let the operating system flush the output buffer when

 # it wants, for better performances (but if you can live with the idea of

 # some data loss consider the default persistence mode that's snapshotting),

 # or on the contrary, use "always" that's very slow but a bit safer than

 # everysec.

 #

 # More details please check the following article:

 # http://antirez.com/post/redis-persistence-demystified.html

 #

 # If unsure, use "everysec".

 # appendfsync always

 appendfsync everysec

 # appendfsync no

 # When the AOF fsync policy is set to always or everysec, and a background

 # saving process (a background save or AOF log background rewriting) is

 # performing a lot of I/O against the disk, in some Linux configurations

 # Redis may block too long on the fsync() call. Note that there is no fix for

 # this currently, as even performing fsync in a different thread will block

 # our synchronous write(2) call.

 #

 # In order to mitigate this problem it's possible to use the following option

 # that will prevent fsync() from being called in the main process while a

 # BGSAVE or BGREWRITEAOF is in progress.

 #

 # This means that while another child is saving, the durability of Redis is

 # the same as "appendfsync none". In practical terms, this means that it is

 # possible to lose up to 30 seconds of log in the worst scenario (with the

 # default Linux settings).

 #

 # If you have latency problems turn this to "yes". Otherwise leave it as

 # "no" that is the safest pick from the point of view of durability.

 no-appendfsync-on-rewrite no

 # Automatic rewrite of the append only file.

 # Redis is able to automatically rewrite the log file implicitly calling

 # BGREWRITEAOF when the AOF log size grows by the specified percentage.

 #

 # This is how it works: Redis remembers the size of the AOF file after the

 # latest rewrite (if no rewrite has happened since the restart, the size of

 # the AOF at startup is used).

 #

 # This base size is compared to the current size. If the current size is

 # bigger than the specified percentage, the rewrite is triggered. Also

 # you need to specify a minimal size for the AOF file to be rewritten, this

 # is useful to avoid rewriting the AOF file even if the percentage increase

 # is reached but it is still pretty small.

 #

 # Specify a percentage of zero in order to disable the automatic AOF

 # rewrite feature.

 auto-aof-rewrite-percentage 100

 auto-aof-rewrite-min-size 64mb

 # An AOF file may be found to be truncated at the end during the Redis

 # startup process, when the AOF data gets loaded back into memory.

 # This may happen when the system where Redis is running

 # crashes, especially when an ext4 filesystem is mounted without the

 # data=ordered option (however this can't happen when Redis itself

 # crashes or aborts but the operating system still works correctly).

 #

 # Redis can either exit with an error when this happens, or load as much

 # data as possible (the default now) and start if the AOF file is found

 # to be truncated at the end. The following option controls this behavior.

 #

 # If aof-load-truncated is set to yes, a truncated AOF file is loaded and

 # the Redis server starts emitting a log to inform the user of the event.

 # Otherwise if the option is set to no, the server aborts with an error

 # and refuses to start. When the option is set to no, the user requires

 # to fix the AOF file using the "redis-check-aof" utility before to restart

 # the server.

 #

 # Note that if the AOF file will be found to be corrupted in the middle

 # the server will still exit with an error. This option only applies when

 # Redis will try to read more data from the AOF file but not enough bytes

 # will be found.

 aof-load-truncated yes

 # When rewriting the AOF file, Redis is able to use an RDB preamble in the

 # AOF file for faster rewrites and recoveries. When this option is turned

 # on the rewritten AOF file is composed of two different stanzas:

 #

 #   [RDB file][AOF tail]

 #

 # When loading Redis recognizes that the AOF file starts with the "REDIS"

 # string and loads the prefixed RDB file, and continues loading the AOF

 # tail.

 #

 # This is currently turned off by default in order to avoid the surprise

 # of a format change, but will at some point be used as the default.

 aof-use-rdb-preamble no

 ################################ LUA SCRIPTING  ###############################

 # Max execution time of a Lua script in milliseconds.

 #

 # If the maximum execution time is reached Redis will log that a script is

 # still in execution after the maximum allowed time and will start to

 # reply to queries with an error.

 #

 # When a long running script exceeds the maximum execution time only the

 # SCRIPT KILL and SHUTDOWN NOSAVE commands are available. The first can be

 # used to stop a script that did not yet called write commands. The second

 # is the only way to shut down the server in the case a write command was

 # already issued by the script but the user doesn't want to wait for the natural

 # termination of the script.

 #

 # Set it to 0 or a negative value for unlimited execution without warnings.

 lua-time-limit 5000

 ################################ REDIS CLUSTER  ###############################

 #

 # ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

 # WARNING EXPERIMENTAL: Redis Cluster is considered to be stable code, however

 # in order to mark it as "mature" we need to wait for a non trivial percentage

 # of users to deploy it in production.

 # ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

 #

 # Normal Redis instances can't be part of a Redis Cluster; only nodes that are

 # started as cluster nodes can. In order to start a Redis instance as a

 # cluster node enable the cluster support uncommenting the following:

 #

 # cluster-enabled yes

 # Every cluster node has a cluster configuration file. This file is not

 # intended to be edited by hand. It is created and updated by Redis nodes.

 # Every Redis Cluster node requires a different cluster configuration file.

 # Make sure that instances running in the same system do not have

 # overlapping cluster configuration file names.

 #

 # cluster-config-file nodes-6379.conf

 # Cluster node timeout is the amount of milliseconds a node must be unreachable

 # for it to be considered in failure state.

 # Most other internal time limits are multiple of the node timeout.

 #

 # cluster-node-timeout 15000

 # A slave of a failing master will avoid to start a failover if its data

 # looks too old.

 #

 # There is no simple way for a slave to actually have an exact measure of

 # its "data age", so the following two checks are performed:

 #

 # 1) If there are multiple slaves able to failover, they exchange messages

 #    in order to try to give an advantage to the slave with the best

 #    replication offset (more data from the master processed).

 #    Slaves will try to get their rank by offset, and apply to the start

 #    of the failover a delay proportional to their rank.

 #

 # 2) Every single slave computes the time of the last interaction with

 #    its master. This can be the last ping or command received (if the master

 #    is still in the "connected" state), or the time that elapsed since the

 #    disconnection with the master (if the replication link is currently down).

 #    If the last interaction is too old, the slave will not try to failover

 #    at all.

 #

 # The point "2" can be tuned by user. Specifically a slave will not perform

 # the failover if, since the last interaction with the master, the time

 # elapsed is greater than:

 #

 #   (node-timeout * slave-validity-factor) + repl-ping-slave-period

 #

 # So for example if node-timeout is 30 seconds, and the slave-validity-factor

 # is 10, and assuming a default repl-ping-slave-period of 10 seconds, the

 # slave will not try to failover if it was not able to talk with the master

 # for longer than 310 seconds.

 #

 # A large slave-validity-factor may allow slaves with too old data to failover

 # a master, while a too small value may prevent the cluster from being able to

 # elect a slave at all.

 #

 # For maximum availability, it is possible to set the slave-validity-factor

 # to a value of 0, which means, that slaves will always try to failover the

 # master regardless of the last time they interacted with the master.

 # (However they'll always try to apply a delay proportional to their

 # offset rank).

 #

 # Zero is the only value able to guarantee that when all the partitions heal

 # the cluster will always be able to continue.

 #

 # cluster-slave-validity-factor 10

 # Cluster slaves are able to migrate to orphaned masters, that are masters

 # that are left without working slaves. This improves the cluster ability

 # to resist to failures as otherwise an orphaned master can't be failed over

 # in case of failure if it has no working slaves.

 #

 # Slaves migrate to orphaned masters only if there are still at least a

 # given number of other working slaves for their old master. This number

 # is the "migration barrier". A migration barrier of 1 means that a slave

 # will migrate only if there is at least 1 other working slave for its master

 # and so forth. It usually reflects the number of slaves you want for every

 # master in your cluster.

 #

 # Default is 1 (slaves migrate only if their masters remain with at least

 # one slave). To disable migration just set it to a very large value.

 # A value of 0 can be set but is useful only for debugging and dangerous

 # in production.

 #

 # cluster-migration-barrier 1

 # By default Redis Cluster nodes stop accepting queries if they detect there

 # is at least an hash slot uncovered (no available node is serving it).

 # This way if the cluster is partially down (for example a range of hash slots

 # are no longer covered) all the cluster becomes, eventually, unavailable.

 # It automatically returns available as soon as all the slots are covered again.

 #

 # However sometimes you want the subset of the cluster which is working,

 # to continue to accept queries for the part of the key space that is still

 # covered. In order to do so, just set the cluster-require-full-coverage

 # option to no.

 #

 # cluster-require-full-coverage yes

 # In order to setup your cluster make sure to read the documentation

 # available at http://redis.io web site.

 ########################## CLUSTER DOCKER/NAT support  ########################

 # In certain deployments, Redis Cluster nodes address discovery fails, because

 # addresses are NAT-ted or because ports are forwarded (the typical case is

 # Docker and other containers).

 #

 # In order to make Redis Cluster working in such environments, a static

 # configuration where each node knows its public address is needed. The

 # following two options are used for this scope, and are:

 #

 # * cluster-announce-ip

 # * cluster-announce-port

 # * cluster-announce-bus-port

 #

 # Each instruct the node about its address, client port, and cluster message

 # bus port. The information is then published in the header of the bus packets

 # so that other nodes will be able to correctly map the address of the node

 # publishing the information.

 #

 # If the above options are not used, the normal Redis Cluster auto-detection

 # will be used instead.

 #

 # Note that when remapped, the bus port may not be at the fixed offset of

 # clients port + 10000, so you can specify any port and bus-port depending

 # on how they get remapped. If the bus-port is not set, a fixed offset of

 # 10000 will be used as usually.

 #

 # Example:

 #

 # cluster-announce-ip 10.1.1.5

 # cluster-announce-port 6379

 # cluster-announce-bus-port 6380

 ################################## SLOW LOG ###################################

 # The Redis Slow Log is a system to log queries that exceeded a specified

 # execution time. The execution time does not include the I/O operations

 # like talking with the client, sending the reply and so forth,

 # but just the time needed to actually execute the command (this is the only

 # stage of command execution where the thread is blocked and can not serve

 # other requests in the meantime).

 #

 # You can configure the slow log with two parameters: one tells Redis

 # what is the execution time, in microseconds, to exceed in order for the

 # command to get logged, and the other parameter is the length of the

 # slow log. When a new command is logged the oldest one is removed from the

 # queue of logged commands.

 # The following time is expressed in microseconds, so 1000000 is equivalent

 # to one second. Note that a negative number disables the slow log, while

 # a value of zero forces the logging of every command.

 slowlog-log-slower-than 10000

 # There is no limit to this length. Just be aware that it will consume memory.

 # You can reclaim memory used by the slow log with SLOWLOG RESET.

 slowlog-max-len 128

 ################################ LATENCY MONITOR ##############################

 # The Redis latency monitoring subsystem samples different operations

 # at runtime in order to collect data related to possible sources of

 # latency of a Redis instance.

 #

 # Via the LATENCY command this information is available to the user that can

 # print graphs and obtain reports.

 #

 # The system only logs operations that were performed in a time equal or

 # greater than the amount of milliseconds specified via the

 # latency-monitor-threshold configuration directive. When its value is set

 # to zero, the latency monitor is turned off.

 #

 # By default latency monitoring is disabled since it is mostly not needed

 # if you don't have latency issues, and collecting data has a performance

 # impact, that while very small, can be measured under big load. Latency

 # monitoring can easily be enabled at runtime using the command

 # "CONFIG SET latency-monitor-threshold <milliseconds>" if needed.

 latency-monitor-threshold 0

 ############################# EVENT NOTIFICATION ##############################

 # Redis can notify Pub/Sub clients about events happening in the key space.

 # This feature is documented at http://redis.io/topics/notifications

 #

 # For instance if keyspace events notification is enabled, and a client

 # performs a DEL operation on key "foo" stored in the Database 0, two

 # messages will be published via Pub/Sub:

 #

 # PUBLISH __keyspace@0__:foo del

 # PUBLISH __keyevent@0__:del foo

 #

 # It is possible to select the events that Redis will notify among a set

 # of classes. Every class is identified by a single character:

 #

 #  K     Keyspace events, published with __keyspace@<db>__ prefix.

 #  E     Keyevent events, published with __keyevent@<db>__ prefix.

 #  g     Generic commands (non-type specific) like DEL, EXPIRE, RENAME, ...

 #  $     String commands

 #  l     List commands

 #  s     Set commands

 #  h     Hash commands

 #  z     Sorted set commands

 #  x     Expired events (events generated every time a key expires)

 #  e     Evicted events (events generated when a key is evicted for maxmemory)

 #  A     Alias for g$lshzxe, so that the "AKE" string means all the events.

 #

 #  The "notify-keyspace-events" takes as argument a string that is composed

 #  of zero or multiple characters. The empty string means that notifications

 #  are disabled.

 #

 #  Example: to enable list and generic events, from the point of view of the

 #           event name, use:

 #

 #  notify-keyspace-events Elg

 #

 #  Example 2: to get the stream of the expired keys subscribing to channel

 #             name __keyevent@0__:expired use:

 #

 #  notify-keyspace-events Ex

 #

 #  By default all notifications are disabled because most users don't need

 #  this feature and the feature has some overhead. Note that if you don't

 #  specify at least one of K or E, no events will be delivered.

 notify-keyspace-events ""

 ############################### ADVANCED CONFIG ###############################

 # Hashes are encoded using a memory efficient data structure when they have a

 # small number of entries, and the biggest entry does not exceed a given

 # threshold. These thresholds can be configured using the following directives.

 hash-max-ziplist-entries 512

 hash-max-ziplist-value 64

 # Lists are also encoded in a special way to save a lot of space.

 # The number of entries allowed per internal list node can be specified

 # as a fixed maximum size or a maximum number of elements.

 # For a fixed maximum size, use -5 through -1, meaning:

 # -5: max size: 64 Kb  <-- not recommended for normal workloads

 # -4: max size: 32 Kb  <-- not recommended

 # -3: max size: 16 Kb  <-- probably not recommended

 # -2: max size: 8 Kb   <-- good

 # -1: max size: 4 Kb   <-- good

 # Positive numbers mean store up to _exactly_ that number of elements

 # per list node.

 # The highest performing option is usually -2 (8 Kb size) or -1 (4 Kb size),

 # but if your use case is unique, adjust the settings as necessary.

 list-max-ziplist-size -2

 # Lists may also be compressed.

 # Compress depth is the number of quicklist ziplist nodes from *each* side of

 # the list to *exclude* from compression.  The head and tail of the list

 # are always uncompressed for fast push/pop operations.  Settings are:

 # 0: disable all list compression

 # 1: depth 1 means "don't start compressing until after 1 node into the list,

 #    going from either the head or tail"

 #    So: [head]->node->node->...->node->[tail]

 #    [head], [tail] will always be uncompressed; inner nodes will compress.

 # 2: [head]->[next]->node->node->...->node->[prev]->[tail]

 #    2 here means: don't compress head or head->next or tail->prev or tail,

 #    but compress all nodes between them.

 # 3: [head]->[next]->[next]->node->node->...->node->[prev]->[prev]->[tail]

 # etc.

 list-compress-depth 0

 # Sets have a special encoding in just one case: when a set is composed

 # of just strings that happen to be integers in radix 10 in the range

 # of 64 bit signed integers.

 # The following configuration setting sets the limit in the size of the

 # set in order to use this special memory saving encoding.

 set-max-intset-entries 512

 # Similarly to hashes and lists, sorted sets are also specially encoded in

 # order to save a lot of space. This encoding is only used when the length and

 # elements of a sorted set are below the following limits:

 zset-max-ziplist-entries 128

 zset-max-ziplist-value 64

 # HyperLogLog sparse representation bytes limit. The limit includes the

 # 16 bytes header. When an HyperLogLog using the sparse representation crosses

 # this limit, it is converted into the dense representation.

 #

 # A value greater than 16000 is totally useless, since at that point the

 # dense representation is more memory efficient.

 #

 # The suggested value is ~ 3000 in order to have the benefits of

 # the space efficient encoding without slowing down too much PFADD,

 # which is O(N) with the sparse encoding. The value can be raised to

 # ~ 10000 when CPU is not a concern, but space is, and the data set is

 # composed of many HyperLogLogs with cardinality in the 0 - 15000 range.

 hll-sparse-max-bytes 3000

 # Active rehashing uses 1 millisecond every 100 milliseconds of CPU time in

 # order to help rehashing the main Redis hash table (the one mapping top-level

 # keys to values). The hash table implementation Redis uses (see dict.c)

 # performs a lazy rehashing: the more operation you run into a hash table

 # that is rehashing, the more rehashing "steps" are performed, so if the

 # server is idle the rehashing is never complete and some more memory is used

 # by the hash table.

 #

 # The default is to use this millisecond 10 times every second in order to

 # actively rehash the main dictionaries, freeing memory when possible.

 #

 # If unsure:

 # use "activerehashing no" if you have hard latency requirements and it is

 # not a good thing in your environment that Redis can reply from time to time

 # to queries with 2 milliseconds delay.

 #

 # use "activerehashing yes" if you don't have such hard requirements but

 # want to free memory asap when possible.

 activerehashing yes

 # The client output buffer limits can be used to force disconnection of clients

 # that are not reading data from the server fast enough for some reason (a

 # common reason is that a Pub/Sub client can't consume messages as fast as the

 # publisher can produce them).

 #

 # The limit can be set differently for the three different classes of clients:

 #

 # normal -> normal clients including MONITOR clients

 # slave  -> slave clients

 # pubsub -> clients subscribed to at least one pubsub channel or pattern

 #

 # The syntax of every client-output-buffer-limit directive is the following:

 #

 # client-output-buffer-limit <class> <hard limit> <soft limit> <soft seconds>

 #

 # A client is immediately disconnected once the hard limit is reached, or if

 # the soft limit is reached and remains reached for the specified number of

 # seconds (continuously).

 # So for instance if the hard limit is 32 megabytes and the soft limit is

 # 16 megabytes / 10 seconds, the client will get disconnected immediately

 # if the size of the output buffers reach 32 megabytes, but will also get

 # disconnected if the client reaches 16 megabytes and continuously overcomes

 # the limit for 10 seconds.

 #

 # By default normal clients are not limited because they don't receive data

 # without asking (in a push way), but just after a request, so only

 # asynchronous clients may create a scenario where data is requested faster

 # than it can read.

 #

 # Instead there is a default limit for pubsub and slave clients, since

 # subscribers and slaves receive data in a push fashion.

 #

 # Both the hard or the soft limit can be disabled by setting them to zero.

 client-output-buffer-limit normal 0 0 0

 client-output-buffer-limit slave 256mb 64mb 60

 client-output-buffer-limit pubsub 32mb 8mb 60

 # Client query buffers accumulate new commands. They are limited to a fixed

 # amount by default in order to avoid that a protocol desynchronization (for

 # instance due to a bug in the client) will lead to unbound memory usage in

 # the query buffer. However you can configure it here if you have very special

 # needs, such us huge multi/exec requests or alike.

 #

 # client-query-buffer-limit 1gb

 # In the Redis protocol, bulk requests, that are, elements representing single

 # strings, are normally limited ot 512 mb. However you can change this limit

 # here.

 #

 # proto-max-bulk-len 512mb

 # Redis calls an internal function to perform many background tasks, like

 # closing connections of clients in timeout, purging expired keys that are

 # never requested, and so forth.

 #

 # Not all tasks are performed with the same frequency, but Redis checks for

 # tasks to perform according to the specified "hz" value.

 #

 # By default "hz" is set to 10. Raising the value will use more CPU when

 # Redis is idle, but at the same time will make Redis more responsive when

 # there are many keys expiring at the same time, and timeouts may be

 # handled with more precision.

 #

 # The range is between 1 and 500, however a value over 100 is usually not

 # a good idea. Most users should use the default of 10 and raise this up to

 # 100 only in environments where very low latency is required.

 hz 10

 # When a child rewrites the AOF file, if the following option is enabled

 # the file will be fsync-ed every 32 MB of data generated. This is useful

 # in order to commit the file to the disk more incrementally and avoid

 # big latency spikes.

 aof-rewrite-incremental-fsync yes

 # Redis LFU eviction (see maxmemory setting) can be tuned. However it is a good

 # idea to start with the default settings and only change them after investigating

 # how to improve the performances and how the keys LFU change over time, which

 # is possible to inspect via the OBJECT FREQ command.

 #

 # There are two tunable parameters in the Redis LFU implementation: the

 # counter logarithm factor and the counter decay time. It is important to

 # understand what the two parameters mean before changing them.

 #

 # The LFU counter is just 8 bits per key, it's maximum value is 255, so Redis

 # uses a probabilistic increment with logarithmic behavior. Given the value

 # of the old counter, when a key is accessed, the counter is incremented in

 # this way:

 #

 # 1. A random number R between 0 and 1 is extracted.

 # 2. A probability P is calculated as 1/(old_value*lfu_log_factor+1).

 # 3. The counter is incremented only if R < P.

 #

 # The default lfu-log-factor is 10. This is a table of how the frequency

 # counter changes with a different number of accesses with different

 # logarithmic factors:

 #

 # +--------+------------+------------+------------+------------+------------+

 # | factor | 100 hits   | 1000 hits  | 100K hits  | 1M hits    | 10M hits   |

 # +--------+------------+------------+------------+------------+------------+

 # | 0      | 104        | 255        | 255        | 255        | 255        |

 # +--------+------------+------------+------------+------------+------------+

 # | 1      | 18         | 49         | 255        | 255        | 255        |

 # +--------+------------+------------+------------+------------+------------+

 # | 10     | 10         | 18         | 142        | 255        | 255        |

 # +--------+------------+------------+------------+------------+------------+

 # | 100    | 8          | 11         | 49         | 143        | 255        |

 # +--------+------------+------------+------------+------------+------------+

 #

 # NOTE: The above table was obtained by running the following commands:

 #

 #   redis-benchmark -n 1000000 incr foo

 #   redis-cli object freq foo

 #

 # NOTE 2: The counter initial value is 5 in order to give new objects a chance

 # to accumulate hits.

 #

 # The counter decay time is the time, in minutes, that must elapse in order

 # for the key counter to be divided by two (or decremented if it has a value

 # less <= 10).

 #

 # The default value for the lfu-decay-time is 1. A Special value of 0 means to

 # decay the counter every time it happens to be scanned.

 #

 # lfu-log-factor 10

 # lfu-decay-time 1

 ########################### ACTIVE DEFRAGMENTATION #######################

 #

 # WARNING THIS FEATURE IS EXPERIMENTAL. However it was stress tested

 # even in production and manually tested by multiple engineers for some

 # time.

 #

 # What is active defragmentation?

 # -------------------------------

 #

 # Active (online) defragmentation allows a Redis server to compact the

 # spaces left between small allocations and deallocations of data in memory,

 # thus allowing to reclaim back memory.

 #

 # Fragmentation is a natural process that happens with every allocator (but

 # less so with Jemalloc, fortunately) and certain workloads. Normally a server

 # restart is needed in order to lower the fragmentation, or at least to flush

 # away all the data and create it again. However thanks to this feature

 # implemented by Oran Agra for Redis 4.0 this process can happen at runtime

 # in an "hot" way, while the server is running.

 #

 # Basically when the fragmentation is over a certain level (see the

 # configuration options below) Redis will start to create new copies of the

 # values in contiguous memory regions by exploiting certain specific Jemalloc

 # features (in order to understand if an allocation is causing fragmentation

 # and to allocate it in a better place), and at the same time, will release the

 # old copies of the data. This process, repeated incrementally for all the keys

 # will cause the fragmentation to drop back to normal values.

 #

 # Important things to understand:

 #

 # 1. This feature is disabled by default, and only works if you compiled Redis

 #    to use the copy of Jemalloc we ship with the source code of Redis.

 #    This is the default with Linux builds.

 #

 # 2. You never need to enable this feature if you don't have fragmentation

 #    issues.

 #

 # 3. Once you experience fragmentation, you can enable this feature when

 #    needed with the command "CONFIG SET activedefrag yes".

 #

 # The configuration parameters are able to fine tune the behavior of the

 # defragmentation process. If you are not sure about what they mean it is

 # a good idea to leave the defaults untouched.

 # Enabled active defragmentation

 # activedefrag yes

 # Minimum amount of fragmentation waste to start active defrag

 # active-defrag-ignore-bytes 100mb

 # Minimum percentage of fragmentation to start active defrag

 # active-defrag-threshold-lower 10

 # Maximum percentage of fragmentation at which we use maximum effort

 # active-defrag-threshold-upper 100

 # Minimal effort for defrag in CPU percentage

 # active-defrag-cycle-min 25

 # Maximal effort for defrag in CPU percentage

 # active-defrag-cycle-max 75

3.3、分别启动主数据库和从数据库

查看从数据库的启动日志如下：

 7187:C 21 Jul 22:21:59.106 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo

 7187:C 21 Jul 22:21:59.107 # Redis version=4.0.8, bits=64, commit=00000000, modified=0, pid=7187, just started

 7187:C 21 Jul 22:21:59.108 # Configuration loaded

 7188:S 21 Jul 22:21:59.110 * Increased maximum number of open files to 10032 (it was originally set to 256).

                 _._

            _.-``__ ''-._

       _.-``    `.  `_.  ''-._           Redis 4.0.8 (00000000/0) 64 bit

   .-`` .-```.  ```\/    _.,_ ''-._

  (    '      ,       .-`  | `,    )     Running in standalone mode

  |`-._`-...-` __...-.``-._|'` _.-'|     Port: 6380

  |    `-._   `._    /     _.-'    |     PID: 7188

   `-._    `-._  `-./  _.-'    _.-'

  |`-._`-._    `-.__.-'    _.-'_.-'|

  |    `-._`-._        _.-'_.-'    |           http://redis.io

   `-._    `-._`-.__.-'_.-'    _.-'

  |`-._`-._    `-.__.-'    _.-'_.-'|

  |    `-._`-._        _.-'_.-'    |

   `-._    `-._`-.__.-'_.-'    _.-'

       `-._    `-.__.-'    _.-'

           `-._        _.-'

               `-.__.-'                                               

 7188:S 21 Jul 22:21:59.120 # Server initialized

 7188:S 21 Jul 22:21:59.121 * DB loaded from disk: 0.000 seconds

 7188:S 21 Jul 22:21:59.122 * Before turning into a slave, using my master parameters to synthesize a cached master: I may be able to synchronize with the new master with just a partial transfer.

 7188:S 21 Jul 22:21:59.122 * Ready to accept connections

 7188:S 21 Jul 22:21:59.123 * Connecting to MASTER 127.0.0.1:6379

 7188:S 21 Jul 22:21:59.123 * MASTER <-> SLAVE sync started

 7188:S 21 Jul 22:21:59.123 * Non blocking connect for SYNC fired the event.

 7188:S 21 Jul 22:21:59.124 * Master replied to PING, replication can continue...

 7188:S 21 Jul 22:21:59.124 * Trying a partial resynchronization (request 9b3c7b84772b004fa9a0999361035b71ecf70ab4:30783).

 7188:S 21 Jul 22:21:59.130 * Full resync from master: cb4fc3545fc3ad62f09ce4f486e0d43ec8f36334:0

 7188:S 21 Jul 22:21:59.130 * Discarding previously cached master state.

 7188:S 21 Jul 22:21:59.163 * MASTER <-> SLAVE sync: receiving 5484 bytes from master

 7188:S 21 Jul 22:21:59.165 * MASTER <-> SLAVE sync: Flushing old data

 7188:S 21 Jul 22:21:59.165 * MASTER <-> SLAVE sync: Loading DB in memory

 7188:S 21 Jul 22:21:59.167 * MASTER <-> SLAVE sync: Finished with success

4、复制的基本操作命令

4.1、info replication : 查看复制节点的相关信息

在主数据库上执行命令：info replication

在从数据库上执行命令：info replication

4.2、slaveof : 可在运行期间修改slave节点的信息，如果该数据已经是某个主数据库的从数据库，那么会停止和原主数据库的同步关系，转而和新的主数据库同步。

4.3、slaveof no one : 使当前数据库停止与其他数据库的同步，转成主数据库

5、复制的基本原理

　　第一步：slave启动时，会向master发送sync命令，2.8版本发送psync，以实现增量复制

　　第二步：主数据库接到sync请求后，会在后台保存快照，也就是实现RDB持久化，并将保存快照期间接收到命令缓存起来

　　第三步：快照完成后，主数据库会将快照文件和所有的缓存的命令发送给从数据库

　　第四步：从数据库接收后，会载入快照文件并执行缓存的命令，从而完成复制的初始化

　　第五步：在数据库使用阶段，主数据库会自动把每次收到的写命令同步到从服务器

6、乐观复制策略

Redis采用乐观复制的策略，容忍在一定时间内主从数据库的内容不同，当然最终的数据还是会一样。这个策略保证了性能，在复制的时候，主数据库并不阻塞，照样处理客户端的请求。

Redis提供了配置来限制只有当数据库至少同步给指定数量的从数据库时，主数据库才可写，否则返回错误。配置是：min-slaves-to-write、min-slaves-max-lag

7、无硬盘复制

当复制发生的时，主数据库会在后台保存RDB快照，即使你关闭了RDB，它也会这么做，这样就会导致：

如果主数据库关闭了RDB，现在强行生成了RDB，那么下次主数据库启动的时候，可能会从RDB来恢复数据，这可能是旧的数据。
由于要生成RDB文件，如果硬盘性能不高的时候，会对性能造成一定影响
因此2.8.18版本，引入了无硬盘复制选项：repl-diskless-sync

8、哨兵（sentinel）

Redis提供了哨兵工具来实现监控Redis系统的运行情况，主要实现：

监控主从数据库运行是否正常
当主数据库出现故障时，自动将从数据库转换为主数据库
使用Redis-sentinel,redis实例必须在非集群模式下运行

开启哨兵功能：

建立一个sentinel.conf文件，里面设置要监控的主数据库的名字，形如：

sentinel monitor 监控的主数据库的名字 127.0.0.1 6379 1 （1-表示选举主数据库的最低票数）

这个文件的内容，在运行期间会被sentinel动态进行更改
可以同时监控多个主数据库，一行一个配置即可

sentinel.conf配置文件如下：

　　sentinel monitor mymaster 127.0.0.1 6379 1

执行启动./redis-sentinel /sentinel.conf命令，日志如下：

9、复制命令

（1）slaveof : 指定某一个redis作为另一个redis的从服务器，通过指定IP和端口来设置主redis，建议为从redis设置一个不同频率的快照持久化周期（建议主redis > 从redis），或者从redis配置一个不同的服务端口

（2）masterauth : 如果主redis设置了验证密码的话（使用requirepass来设置）,则在从redis的配置中要使用masterauth来设置校验密码，否则的话，主redis会拒绝从redis的访问请求

（3）slave-serve-stale-data ：设置当从redis失去了与主redis的连接，或者主从同步在进行中时，redis该如何处理外部发来的访问请求

如果设置为yes(默认),则从redis仍会继续响应客户端的读写请求。

如果设置为no,则从redis会对客户端的请求返回"SYNC with master in process"，当然也有例外，当客户端发送INFO请求和SLAVEOF请求，从redis还是会进行处理，从redis2.6版本之后，默认从redis为只读。

（4）slave-read-only : 设置从redis为只读

（5）repl-ping-slave-period : 设置从redis会向主redis发出PING包的周期，默认是10秒。

（6）repl-timeout : 设置主从同步的超时时间，要确保这个时限比repl-ping-slave-period的值要大，否则每次主redis都会认为从redis超时。

（7）repl-disable-tcp-nodelay : 设置在主从同步时是否禁用TCP_NODELAY,如果开启，那么主redis会使用更少的TCP包和更少的带宽来向从redis传输数据，但是这可能会增加一些同步的延迟，大概会达到40毫秒左右。如果关闭，那么数据同步的延迟时间会降低，但是会消耗等多的带宽

（8）repl-backlog-size : 设置同步队列长度。队列长度(backlog)是主redis中的一个缓冲区，在与从redis断开连接期间，主redis会用这个缓冲区来缓存应该发给从redis的数据，这样的话，当从redis重新连接上之后，就不必重新全量同步数据，只需要同步这部分增量数据即可。

（9）repl-backlog-ttl : 设置主redis要等待的时间长度，如果主redis等了这么长时间之后，还是无法连接到从redis，那么缓冲队列的数据将被清理掉。设置为0，则表示永远不清理，默认是1个小时

（10）slave-priority : 设置从redis优先级，在主redis持续工作不正常的情况下，优先级高的从redis将会升级为主redis。而编号越小，优先级越高。当优先级被设置为0时，这个从redis将永远也不会被选中，默认的优先级为100.

（11）min-slaves-to-write : 设置执行写操作所需要的最少从服务器数量，如果至少有这么多个从服务器，并且这些服务器的延迟值都少于min-slaves-max-lag秒，那么主服务器就会执行客户端请求的写操作。

（12）min-slaves-max-lag : 设置最大连接延迟的时间，min-slaves-to-write和min-slaves-max-lag中有一个被设置为0，则这个特性将被关闭。默认情况下min-slaves-to-write为0，而min-slaves-max-lag为10

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