PXC中的GTIDs
基本环境：PXC 5.7.19 Row+Gtid，3节点
一、Galera GTID vs MySQL GTID
1.1、Galera GTID vs MySQL GTID
Both kinds of GTIDs are using the same format: <source_id:trx_number>.
For Galera, <source_id> is generated when the cluster is bootstrapped. This <source_id> is shared by all nodes.
For MySQL, <source_id> is the server uuid. So it is easy to identify from which server a transaction originates.
我们先来看下PXC环境Galera GTID和MySQL GTID分别指的是什么
# node1的server_uuid
mydba@192.168.85.132,3326 [replcrash]> select @@server_uuid;
+--------------------------------------+
| @@server_uuid |
+--------------------------------------+
| 31304898-67d8-11e8-bb20-000c29c1025c |
+--------------------------------------+
1 row in set (0.00 sec)
# node1写入一条数据
mydba@192.168.85.132,3326 [replcrash]> insert into py_user(name,add_time,server_id) select left(uuid(),32),now(),@@server_id;
Query OK, 1 row affected (0.02 sec)
Records: 1 Duplicates: 0 Warnings: 0
# node1查看gtid_executed
mydba@192.168.85.132,3326 [replcrash]> select @@global.gtid_executed;
+----------------------------------------+
| @@global.gtid_executed |
+----------------------------------------+
| 0f0f1664-9769-ee17-7834-ec71884d9f25:1 |
+----------------------------------------+
1 row in set (0.00 sec) # node2的server_uuid
mydba@192.168.85.133,3326 [replcrash]> select @@server_uuid;
+--------------------------------------+
| @@server_uuid |
+--------------------------------------+
| 570e2242-6898-11e8-bcae-000c2900c99c |
+--------------------------------------+
1 row in set (0.01 sec)
# node2写入一条数据
mydba@192.168.85.133,3326 [replcrash]> insert into py_user(name,add_time,server_id) select left(uuid(),32),now(),@@server_id;
Query OK, 1 row affected (0.45 sec)
Records: 1 Duplicates: 0 Warnings: 0
# node2查看gtid_executed
mydba@192.168.85.133,3326 [replcrash]> select @@global.gtid_executed;
+------------------------------------------+
| @@global.gtid_executed |
+------------------------------------------+
| 0f0f1664-9769-ee17-7834-ec71884d9f25:1-2 |
+------------------------------------------+
1 row in set (0.00 sec)
上面@@server_uuid对应的是MySQL，@@global.gtid_executed对应的是Galera
node1、node2上执行的insert语句使用相同的<source_id>，仿佛它们在同一台实例上执行，并且与node1/node2自己的@@server_uuid不同
我们可以把Cluster当作MySQL复制中的Master，所有节点获取来自相同<source_id>的数据
1.2、UUID
我们知道MySQL GTID的<source_id>存储于$/datadir/auto.cnf，Galera GTID的<source_id>是否也存在相关的文件？如果你足够仔细的话，你会发现Galera GTID与$/datadir/grastate.dat存在下面的关联
# 查看grastate.dat
[root@ZST1 data]# cat grastate.dat
# GALERA saved state
version: 2.1
uuid: f0f0e99b--11e8-87cb-138e77b260da
seqno: -
safe_to_bootstrap:
[root@ZST1 data]# # Galera GTID与$/datadir/grastate.dat的关联
Galera GTID<source_id> + grastate.dat<uuid>
= 0f0f1664--ee17--ec71884d9f25 + f0f0e99b--11e8-87cb-138e77b260da
= ffffffff-ffff-ffff-ffff-ffffffffffff
Cluster的第一节点启动时，会读取grastate.dat文件，用它里面的uuid信息构建Galera GTID的<source_id>。如果删除$/datadir/grastate.dat文件，下次重新启动集群，它的Galera GTID会改变(类似删除$/datadir/auto.cnf文件，重新启动实例MySQL GTID也会改变)。Galera GTID与MySQL GTID之间并没有对应关系，它们是相互独立的。PXC中的@@global.gtid_executed的初始化可以参考：gtid_executed和gtid_purged变量是如何初始化的，只要明白Galera GTID的<source_id>来源，其他完全可以套用MySQL GTID
PXC中其实还存在其他uuid
mydba@192.168.85.132,3326 [replcrash]> show status like '%uuid%';
+--------------------------+--------------------------------------+
| Variable_name | Value |
+--------------------------+--------------------------------------+
| wsrep_local_state_uuid | f0f0e99b-6896-11e8-87cb-138e77b260da |
| wsrep_gcomm_uuid | 8ab36be3-6897-11e8-bf70-cee6630daa30 |
| wsrep_cluster_state_uuid | f0f0e99b-6896-11e8-87cb-138e77b260da |
+--------------------------+--------------------------------------+
3 rows in set (0.00 sec) wsrep_cluster_state_uuid
Provides the current State UUID. This is a unique identifier for the current state of the cluster and the sequence of changes it undergoes. wsrep_local_state_uuid
The UUID of the state stored on this node. wsrep_gcomm_uuid
Displays the group communications UUID.
wsrep_cluster_state_uuid、wsrep_local_state_uuid对应的就是grastate.dat中的uuid，wsrep_gcomm_uuid是group communications uuid
二、什么情况下当前节点的事务不会复制到其他节点
普通主从环境，从库@@global.gtid_executed只会显示主库执行的事务。如果我们在从库手动执行事务，那么从库@@global.gtid_executed就会包含本地的信息
对于PXC来说，它支持多节点写入，任何节点的DML操作先在本地执行，在提交前将所有的变更和对应主键保存到write-set，集群下发write-set给每个节点(包括DML执行的节点)，使用主键验证各节点是否可以应用write-set。如果验证失败，则删除write-set并回滚原始事务；如果验证成功，提交事务并应用其他未完成的write-set。
是不是任何节点上的任何事务都能复制所有节点？有没有可能某个事务只存在于一个节点？
• DML On MyISAM
最大的可能是对MyISAM表的DML操作，会使用server_uuid记录binlog，并且不会被复制到集群中的其他节点！
# node1创建myisam引擎的表
mydba@192.168.85.132,3326 [replcrash]> create table py_user_myisam(id int not null primary key) engine=myisam;
Query OK, 0 rows affected (0.66 sec)
# 往py_user_myisam表中插入数据
mydba@192.168.85.132,3326 [replcrash]> insert into py_user_myisam(id) select 1;
ERROR 1105 (HY000): Percona-XtraDB-Cluster prohibits use of DML command on a table (replcrash.py_user_myisam) that resides in non-transactional storage engine with pxc_strict_mode = ENFORCING or MASTER
# 修改mode为permissive
mydba@192.168.85.132,3326 [replcrash]> set global pxc_strict_mode='permissive';
Query OK, 0 rows affected (0.00 sec)
# 重新插入数据
mydba@192.168.85.132,3326 [replcrash]> insert into py_user_myisam(id) select 1;
Query OK, 1 row affected, 1 warning (0.09 sec)
Records: 1 Duplicates: 0 Warnings: 1
# node1查看gtid_executed
mydba@192.168.85.132,3326 [replcrash]> select @@global.gtid_executed;
+----------------------------------------------------------------------------------+
| @@global.gtid_executed |
+----------------------------------------------------------------------------------+
| 0f0f1664-9769-ee17-7834-ec71884d9f25:1-3,
31304898-67d8-11e8-bb20-000c29c1025c:1 |
+----------------------------------------------------------------------------------+
1 row in set (0.00 sec)
# 查看binlog events
mydba@192.168.85.132,3326 [replcrash]> show binlog events in 'mysql-bin.000003';
+------------------+-----+----------------+-----------+-------------+-----------------------------------------------------------------------------------------+
| Log_name | Pos | Event_type | Server_id | End_log_pos | Info |
+------------------+-----+----------------+-----------+-------------+-----------------------------------------------------------------------------------------+
| mysql-bin.000003 | 4 | Format_desc | 1323326 | 123 | Server ver: 5.7.19-17-29.22-log, Binlog ver: 4 |
| mysql-bin.000003 | 123 | Previous_gtids | 1323326 | 194 | 0f0f1664-9769-ee17-7834-ec71884d9f25:1 |
| mysql-bin.000003 | 194 | Gtid | 1333326 | 259 | SET @@SESSION.GTID_NEXT= '0f0f1664-9769-ee17-7834-ec71884d9f25:2' |
| mysql-bin.000003 | 259 | Query | 1333326 | 327 | BEGIN |
| mysql-bin.000003 | 327 | Table_map | 1333326 | 390 | table_id: 121 (replcrash.py_user) |
| mysql-bin.000003 | 390 | Write_rows | 1333326 | 476 | table_id: 121 flags: STMT_END_F |
| mysql-bin.000003 | 476 | Xid | 1333326 | 507 | COMMIT /* xid=3 */ |
| mysql-bin.000003 | 507 | Gtid | 1323326 | 572 | SET @@SESSION.GTID_NEXT= '0f0f1664-9769-ee17-7834-ec71884d9f25:3' |
| mysql-bin.000003 | 572 | Query | 1323326 | 726 | use `replcrash`; create table py_user_myisam(id int not null primary key) engine=myisam |
| mysql-bin.000003 | 726 | Gtid | 1323326 | 791 | SET @@SESSION.GTID_NEXT= '31304898-67d8-11e8-bb20-000c29c1025c:1' |
| mysql-bin.000003 | 791 | Query | 1323326 | 873 | BEGIN |
| mysql-bin.000003 | 873 | Table_map | 1323326 | 935 | table_id: 224 (replcrash.py_user_myisam) |
| mysql-bin.000003 | 935 | Write_rows | 1323326 | 975 | table_id: 224 flags: STMT_END_F |
| mysql-bin.000003 | 975 | Query | 1323326 | 1058 | COMMIT |
+------------------+-----+----------------+-----------+-------------+-----------------------------------------------------------------------------------------+
14 rows in set (0.05 sec) # node2查看gtid_executed
mydba@192.168.85.133,3326 [replcrash]> select @@global.gtid_executed;
+------------------------------------------+
| @@global.gtid_executed |
+------------------------------------------+
| 0f0f1664-9769-ee17-7834-ec71884d9f25:1-3 |
+------------------------------------------+
1 row in set (0.10 sec)
创建MyISAM表的语句使用DDL机制，它能复制到各节点；但是对MyISAM表执行DML操作，它使用@@server_uuid(类似常规MySQL复制)，不会复制到Cluster的其他节点，但是它能复制到node1节点的异步Slave
• Flush Commands
# node1执行flush privileges
mydba@192.168.85.132,3326 [replcrash]> flush privileges;
Query OK, 0 rows affected (0.26 sec)
# node1查看gtid_executed
mydba@192.168.85.132,3326 [replcrash]> select @@global.gtid_executed;
+----------------------------------------------------------------------------------+
| @@global.gtid_executed |
+----------------------------------------------------------------------------------+
| 0f0f1664-9769-ee17-7834-ec71884d9f25:1-4,
31304898-67d8-11e8-bb20-000c29c1025c:1 |
+----------------------------------------------------------------------------------+
1 row in set (0.00 sec)
# node1查看binlog events
mydba@192.168.85.132,3326 [replcrash]> show binlog events in 'mysql-bin.000003';
+------------------+------+----------------+-----------+-------------+-----------------------------------------------------------------------------------------+
| Log_name | Pos | Event_type | Server_id | End_log_pos | Info |
+------------------+------+----------------+-----------+-------------+-----------------------------------------------------------------------------------------+
| mysql-bin.000003 | 4 | Format_desc | 1323326 | 123 | Server ver: 5.7.19-17-29.22-log, Binlog ver: 4 |
| mysql-bin.000003 | 123 | Previous_gtids | 1323326 | 194 | 0f0f1664-9769-ee17-7834-ec71884d9f25:1 |
| mysql-bin.000003 | 194 | Gtid | 1333326 | 259 | SET @@SESSION.GTID_NEXT= '0f0f1664-9769-ee17-7834-ec71884d9f25:2' |
| mysql-bin.000003 | 259 | Query | 1333326 | 327 | BEGIN |
| mysql-bin.000003 | 327 | Table_map | 1333326 | 390 | table_id: 121 (replcrash.py_user) |
| mysql-bin.000003 | 390 | Write_rows | 1333326 | 476 | table_id: 121 flags: STMT_END_F |
| mysql-bin.000003 | 476 | Xid | 1333326 | 507 | COMMIT /* xid=3 */ |
| mysql-bin.000003 | 507 | Gtid | 1323326 | 572 | SET @@SESSION.GTID_NEXT= '0f0f1664-9769-ee17-7834-ec71884d9f25:3' |
| mysql-bin.000003 | 572 | Query | 1323326 | 726 | use `replcrash`; create table py_user_myisam(id int not null primary key) engine=myisam |
| mysql-bin.000003 | 726 | Gtid | 1323326 | 791 | SET @@SESSION.GTID_NEXT= '31304898-67d8-11e8-bb20-000c29c1025c:1' |
| mysql-bin.000003 | 791 | Query | 1323326 | 873 | BEGIN |
| mysql-bin.000003 | 873 | Table_map | 1323326 | 935 | table_id: 224 (replcrash.py_user_myisam) |
| mysql-bin.000003 | 935 | Write_rows | 1323326 | 975 | table_id: 224 flags: STMT_END_F |
| mysql-bin.000003 | 975 | Query | 1323326 | 1058 | COMMIT |
| mysql-bin.000003 | 1058 | Gtid | 1323326 | 1123 | SET @@SESSION.GTID_NEXT= '0f0f1664-9769-ee17-7834-ec71884d9f25:4' |
| mysql-bin.000003 | 1123 | Query | 1323326 | 1219 | use `replcrash`; flush privileges |
+------------------+------+----------------+-----------+-------------+-----------------------------------------------------------------------------------------+
16 rows in set (0.00 sec) # node2查看gtid_executed
mydba@192.168.85.133,3326 [replcrash]> select @@global.gtid_executed;
+------------------------------------------+
| @@global.gtid_executed |
+------------------------------------------+
| 0f0f1664-9769-ee17-7834-ec71884d9f25:1-4 |
+------------------------------------------+
1 row in set (0.00 sec)
# node2查看binlog events
mydba@192.168.85.133,3326 [replcrash]> show binlog events in 'mysql-bin.000004';
+------------------+-----+----------------+-----------+-------------+-----------------------------------------------------------------------------------------+
| Log_name | Pos | Event_type | Server_id | End_log_pos | Info |
+------------------+-----+----------------+-----------+-------------+-----------------------------------------------------------------------------------------+
| mysql-bin.000004 | 4 | Format_desc | 1333326 | 123 | Server ver: 5.7.19-17-29.22-log, Binlog ver: 4 |
| mysql-bin.000004 | 123 | Previous_gtids | 1333326 | 194 | 0f0f1664-9769-ee17-7834-ec71884d9f25:1 |
| mysql-bin.000004 | 194 | Gtid | 1333326 | 259 | SET @@SESSION.GTID_NEXT= '0f0f1664-9769-ee17-7834-ec71884d9f25:2' |
| mysql-bin.000004 | 259 | Query | 1333326 | 349 | BEGIN |
| mysql-bin.000004 | 349 | Table_map | 1333326 | 412 | table_id: 121 (replcrash.py_user) |
| mysql-bin.000004 | 412 | Write_rows | 1333326 | 498 | table_id: 121 flags: STMT_END_F |
| mysql-bin.000004 | 498 | Xid | 1333326 | 529 | COMMIT /* xid=3 */ |
| mysql-bin.000004 | 529 | Gtid | 1323326 | 594 | SET @@SESSION.GTID_NEXT= '0f0f1664-9769-ee17-7834-ec71884d9f25:3' |
| mysql-bin.000004 | 594 | Query | 1323326 | 748 | use `replcrash`; create table py_user_myisam(id int not null primary key) engine=myisam |
| mysql-bin.000004 | 748 | Gtid | 1323326 | 813 | SET @@SESSION.GTID_NEXT= '0f0f1664-9769-ee17-7834-ec71884d9f25:4' |
| mysql-bin.000004 | 813 | Query | 1323326 | 909 | use `replcrash`; flush privileges |
+------------------+-----+----------------+-----------+-------------+-----------------------------------------------------------------------------------------+
11 rows in set (0.00 sec)
实验表明，flush命令被正常复制到其他节点，binlog中使用的是Cluster UUID。看来Issuing FLUSH commands on a node will create a local transaction on GTID-configured clusters已经被修复●-●
• SQL_LOG_BIN=0
在当前节点 SET SQL_LOG_BIN=0，不会记录对应的binlog，难道就没有对应的write-set？这种情况对于事后也没办法知道原始事务发生在哪个节点，没GTID，没binlog，太阔怕･ω･
三、参考文档
Percona XtraDB Cluster 5.6: a tale of 2 GTIDs：https://www.percona.com/blog/2015/02/13/percona-xtradb-cluster-5-6-a-tale-of-2-mysql-gtids/
How to setup a PXC cluster with GTIDs (and have async slaves replicating from it!)：https://www.percona.com/blog/2015/02/20/how-to-setup-a-pxc-cluster-with-gtids-and-have-async-slaves-replicating-from-it/
Webinar Q/A: MySQL High Availability with Percona XtraDB Cluster 5.7：http://feed.askmaclean.com/archives/webinar-qa-mysql-high-availability-with-percona-xtradb-cluster-5-7.html
GALERA CLUSTER DOCUMENTATION：http://galeracluster.com/documentation-webpages/index.html
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