13518219792
03全局序列号篇详细介绍了分片表, 业务在使用分片表时, 很自然的可能会遇到一个事务中操作的数据分布在多个分片节点上, 即分布式事务. 先来直观感受下Mycat处理事务的过程.
在网站制作、成都网站制作过程中，需要针对客户的行业特点、产品特性、目标受众和市场情况进行定位分析，以确定网站的风格、色彩、版式、交互等方面的设计方向。成都创新互联公司还需要根据客户的需求进行功能模块的开发和设计，包括内容管理、前台展示、用户权限管理、数据统计和安全保护等功能。
登陆tb3表的dnTest2节点主机, 操作如下.
MySQL> set global innodb_lock_wait_timeout = 5;
Query OK, 0 rows affected (0.00 sec)
mysql> start transaction;
Query OK, 0 rows affected (0.00 sec)
mysql> select user_name from tb3 where user_id = 59 for update;
+-----------+
| user_name |
+-----------+
| mnop_f |
+-----------+
1 row in set (0.00 sec)
登陆Mycat, 开启一个事务, 结合日志看下该过程.
mysql> start transaction;
Query OK, 0 rows affected (0.01 sec)
mysql> update tb3 set user_name = 'igkl_2f' where user_id = 4;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> update tb3 set user_name = 'mnop_2f' where user_id = 59;
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
mysql> commit;
ERROR 1003 (HY000): Transaction error, need to rollback.
mysql> rollback;
Query OK, 0 rows affected (0.00 sec)
关键日志如下.
03/27 12:07:09.189 DEBUG [$_NIOREACTOR-1-RW] (ServerQueryHandler.java:56) -ServerConnection [id=2, schema=testdb, host=192.168.4.184, user=test_user,txIsolation=3, autocommit=true, schema=testdb]begin
03/27 12:16:33.019 DEBUG [$_NIOREACTOR-2-RW] (ServerQueryHandler.java:56) -ServerConnection [id=6, schema=testdb, host=192.168.4.184, user=test_user,txIsolation=3, autocommit=false, schema=testdb]update tb3 set user_name = 'igkl_2f' where user_id = 4
03/27 12:16:33.021 DEBUG [$_NIOREACTOR-2-RW] (NonBlockingSession.java:113) -ServerConnection [id=6, schema=testdb, host=192.168.4.184, user=test_user,txIsolation=3, autocommit=false, schema=testdb]update tb3 set user_name = 'igkl_2f' where user_id = 4, route={
1 -> dnTest1{update tb3 set user_name = 'igkl_2f' where user_id = 4}
03/27 12:16:33.021 DEBUG [$_NIOREACTOR-2-RW] (MySQLConnection.java:459) -con need syn ,total syn cmd 3 commands SET names utf8;SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;SET autocommit=0;schema change:false con:MySQLConnection [id=8, lastTime=1522124193021, user=appacc, schema=test1, old shema=test1, borrowed=true, fromSlaveDB=false, threadId=28, charset=utf8, txIsolation=0, autocommit=true, attachment=dnTest1{update tb3 set user_name = 'igkl_2f' where user_id = 4}, respHandler=SingleNodeHandler [node=dnTest1{update tb3 set user_name = 'igkl_2f' where user_id = 4}, packetId=0], host=192.168.4.235, port=3306, statusSync=null, writeQueue=0, modifiedSQLExecuted=true]
03/27 12:16:52.795 DEBUG [$_NIOREACTOR-2-RW] (ServerQueryHandler.java:56) -ServerConnection [id=6, schema=testdb, host=192.168.4.184, user=test_user,txIsolation=3, autocommit=false, schema=testdb]update tb3 set user_name = 'mnop_2f' where user_id = 59
03/27 12:16:52.796 DEBUG [$_NIOREACTOR-2-RW] (NonBlockingSession.java:113) -ServerConnection [id=6, schema=testdb, host=192.168.4.184, user=test_user,txIsolation=3, autocommit=false, schema=testdb]update tb3 set user_name = 'mnop_2f' where user_id = 59, route={
1 -> dnTest2{update tb3 set user_name = 'mnop_2f' where user_id = 59}
03/27 12:16:52.797 DEBUG [$_NIOREACTOR-2-RW] (MySQLConnection.java:459) -con need syn ,total syn cmd 3 commands SET names utf8;SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;SET autocommit=0;schema change:false con:MySQLConnection [id=20, lastTime=1522124212797, user=appacc, schema=test2, old shema=test2, borrowed=true, fromSlaveDB=false, threadId=8, charset=utf8, txIsolation=0, autocommit=true, attachment=dnTest2{update tb3 set user_name = 'mnop_2f' where user_id = 59}, respHandler=SingleNodeHandler [node=dnTest2{update tb3 set user_name = 'mnop_2f' where user_id = 59}, packetId=0], host=192.168.4.151, port=3306, statusSync=null, writeQueue=0, modifiedSQLExecuted=true]
03/27 12:16:58.800 WARN [$_NIOREACTOR-1-RW] (SingleNodeHandler.java:232) -execute sql err : errno:1205 Lock wait timeout exceeded; try restarting transaction con:MySQLConnection [id=20, lastTime=1522124212784, user=appacc, schema=test2, old shema=test2, borrowed=true, fromSlaveDB=false, threadId=8, charset=utf8, txIsolation=3, autocommit=false, attachment=dnTest2{update tb3 set user_name = 'mnop_2f' where user_id = 59}, respHandler=SingleNodeHandler [node=dnTest2{update tb3 set user_name = 'mnop_2f' where user_id = 59}, packetId=1], host=192.168.4.151, port=3306, statusSync=org.opencloudb.mysql.nio.MySQLConnection$StatusSync@52530466, writeQueue=0, modifiedSQLExecuted=true] frontend host:192.168.4.184/59858/test_user
03/27 12:17:05.660 DEBUG [$_NIOREACTOR-2-RW] (ServerQueryHandler.java:56) -ServerConnection [id=6, schema=testdb, host=192.168.4.184, user=test_user,txIsolation=3, autocommit=false, schema=testdb]commit
03/27 12:17:08.868 DEBUG [$_NIOREACTOR-2-RW] (ServerQueryHandler.java:56) -ServerConnection [id=6, schema=testdb, host=192.168.4.184, user=test_user,txIsolation=3, autocommit=false, schema=testdb]rollback
03/27 12:17:08.870 DEBUG [$_NIOREACTOR-2-RW] (RollbackNodeHandler.java:79) -rollback job run for MySQLConnection [id=20, lastTime=1522124212784, user=appacc, schema=test2, old shema=test2, borrowed=true, fromSlaveDB=false, threadId=8, charset=utf8, txIsolation=3, autocommit=false, attachment=dnTest2{update tb3 set user_name = 'mnop_2f' where user_id = 59}, respHandler=SingleNodeHandler [node=dnTest2{update tb3 set user_name = 'mnop_2f' where user_id = 59}, packetId=1], host=192.168.4.151, port=3306, statusSync=org.opencloudb.mysql.nio.MySQLConnection$StatusSync@52530466, writeQueue=0, modifiedSQLExecuted=true]
03/27 12:17:08.870 DEBUG [$_NIOREACTOR-2-RW] (RollbackNodeHandler.java:79) -rollback job run for MySQLConnection [id=8, lastTime=1522124193010, user=appacc, schema=test1, old shema=test1, borrowed=true, fromSlaveDB=false, threadId=28, charset=utf8, txIsolation=3, autocommit=false, attachment=dnTest1{update tb3 set user_name = 'igkl_2f' where user_id = 4}, respHandler=SingleNodeHandler [node=dnTest1{update tb3 set user_name = 'igkl_2f' where user_id = 4}, packetId=1], host=192.168.4.235, port=3306, statusSync=null, writeQueue=0, modifiedSQLExecuted=true]
Mycat目前对于未分片的节点, 是可以保证事务的完整性的; 若是多个分片节点, 在执行事务时, 遇到任何分片出错, 也是能保证所有分片回滚的, 即上边展示的情况. 可是应用一旦进入commit过程, 若此时出现问题, 其就无能为力了, 这也是Mycat称之为弱XA的原因.
上述commit过程是指: InnoDB prepare, write/sync Binlog, InnoDB commit(其历经5.5至5.7版本的多次迭代优化, 这块内容也是精彩纷呈). 虽该阶段一般不会出现问题, 这也正暗示了Mycat在特殊情况下还不能保证分布式事务安全. 那应用架构中又如何实现可靠的分布式事务呢, 这又是另一个宏大的话题了...
若感兴趣可关注订阅号”数据库最佳实践”(DBBestPractice).
