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
   `-._    `-._  `-./  _.-'    _.-'
  |`-._`-._    `-.__.-'    _.-'_.-'|
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 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：

1. 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。
2. 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
3. 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