mycat ShareJoin后少了2条记录的问题剖析详细过程

--<>问题描述

Mycat 在进行join的时候，本来是应该join出4条记录，但是结果却只出来2条记录，问题在哪里？

mycat版本是1.5 mysql版本是5.6.12-log

1，准备环境，先去原始mysql库上执行建库录入数据操作

# 在db1库和db2库分别建2个测试表 mysql> use db1 Database changed mysql> CREATE TABLE `t1` ( -> `id` bigint(20) NOT NULL AUTO_INCREMENT, -> `name` varchar(200) DEFAULT NULL, -> PRIMARY KEY (`id`) -> ) ENGINE=InnoDB AUTO_INCREMENT=2001 DEFAULT CHARSET=utf8; Query OK, 0 rows affected (0.00 sec) mysql> CREATE TABLE `t2` ( -> `id` bigint(20) NOT NULL AUTO_INCREMENT, -> `name` varchar(200) DEFAULT NULL, -> `parent_id` bigint(20) DEFAULT NULL, -> PRIMARY KEY (`id`) -> ) ENGINE=InnoDB AUTO_INCREMENT=2001 DEFAULT CHARSET=utf8; Query OK, 0 rows affected (0.00 sec) mysql> use db2 Database changed mysql> CREATE TABLE `t1` ( -> `id` bigint(20) NOT NULL AUTO_INCREMENT, -> `name` varchar(200) DEFAULT NULL, -> PRIMARY KEY (`id`) -> ) ENGINE=InnoDB AUTO_INCREMENT=2001 DEFAULT CHARSET=utf8; r(200) DEFAULT NULL, `parent_id` bigint(20) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=2001 DEFAULT CHARSET=utf8; Query OK, 0 rows affected (0.01 sec) mysql> CREATE TABLE `t2` ( -> `id` bigint(20) NOT NULL AUTO_INCREMENT, -> `name` varchar(200) DEFAULT NULL, -> `parent_id` bigint(20) DEFAULT NULL, -> PRIMARY KEY (`id`) -> ) ENGINE=InnoDB AUTO_INCREMENT=2001 DEFAULT CHARSET=utf8; Query OK, 0 rows affected (0.01 sec) mysql> # 也是在mysql中执行，开始录入数据 mysql> Insert into db2.t1(id,name) values(1,'db2'); Query OK, 1 row affected (0.01 sec) mysql> Insert into db1.t1(id,name) values(2,'db1'); db1.2',1); Insert into db2.t2(id,name,parent_id) values(3,'db2.2',2);Query OK, 1 row affected (0.00 sec) mysql> Insert into db1.t2(id,name,parent_id) values(2,'db1.1',1); Query OK, 1 row affected (0.00 sec) mysql> Insert into db1.t2(id,name,parent_id) values(4,'db2.2',2); Query OK, 1 row affected (0.00 sec) mysql> Insert into db2.t2(id,name,parent_id) values(1,'db1.2',1); Query OK, 1 row affected (0.00 sec) mysql> Insert into db2.t2(id,name,parent_id) values(3,'db2.2',2); Query OK, 1 row affected (0.01 sec) mysql>

请注意，重点来了，按照正常的理解，2个节点的t1表有2条记录，2个节点的t2表有4条记录，那么表关联后应该返回4条记录，对不对？

那么mycat到底给我们返回了几条记录呢是不是4条呢？

答案是否定的！！！！！！！接下来配置mycat吧，实际验证一下。

2，mycat中schema.xml配置

Schema.xml配置：

# table表配置 <table name="t1" dataNode="dn1,dn2" rule="mod-long" primaryKey="id" /> <table name="t2" dataNode="dn2,dn1" rule="mod-long" primaryKey="id" /> # datanode配置 <dataNode name="dn1" dataHost="dh1" database="db1" /> <dataNode name="dn2" dataHost="dh1" database="db2" /> # datahost配置 <dataHost name="dh1" maxCon="1000" minCon="10" balance="0" writeType="0" dbType="mysql" dbDriver="native" switchType="1" slaveThreshold="100"> <heartbeat>select user()</heartbeat> <writeHost host="hostM1" url="192.168.121.61:3306" user="root" password=""/> </dataHost>

3，重启mycat

[root@oracle_standby ~]# mycat restart Stopping Mycat-server... Stopped Mycat-server. Starting Mycat-server... [root@oracle_standby ~]#

文章源地址：/article/7549630.html，谢绝转载

4，查看mycat执行结果

# 单表查询t1有2条记录，正常 mysql> select * from t1; +----+------+ | id | name | +----+------+ | 2 | db1 | | 1 | db2 | +----+------+ 2 rows in set (0.01 sec) # 单表查询t2有4条记录，正常 mysql> select * from t2; +----+-------+-----------+ | id | name | parent_id | +----+-------+-----------+ | 1 | db1.2 | 1 | | 3 | db2.2 | 2 | | 2 | db1.1 | 1 | | 4 | db2.2 | 2 | +----+-------+-----------+ 4 rows in set (0.01 sec) # 那么t1 通过parent_id关联t2表，应该有4条记录，对不对？但是只有2条，而且加了ShareJoin前后的查询出来的数据还不一样，如下所示： mysql> select * from t1,t2 where t1.id = t2.parent_id; +----+------+----+-------+-----------+ | id | name | id | name | parent_id | +----+------+----+-------+-----------+ | 2 | db1 | 4 | db2.2 | 2 | | 1 | db2 | 1 | db1.2 | 1 | +----+------+----+-------+-----------+ 2 rows in set (0.01 sec) mysql> /*!mycat:catlet=demo.catlets.ShareJoin */ select t1.*,t2.* from t1,t2 where t1.id = t2.parent_id; +----+------+-------+-----------+ | id | name | name | parent_id | +----+------+-------+-----------+ | 1 | db2 | db1.1 | 1 | | 2 | db1 | db2.2 | 2 | +----+------+-------+-----------+ 2 rows in set (0.02 sec) mysql> # 看到加了注解走了mycat后，结果集不一样了，问题在哪里呢？

5，Mycat.log分析

05/04 17:21:11.443 DEBUG [$_NIOREACTOR-0-RW] (ServerQueryHandler.java:56) -ServerConnection [id=1, schema=TESTDB, host=127.0.0.1, user=test,txIsolation=3, autocommit=true, schema=TESTDB]/*!mycat:catlet=demo.catlets.ShareJoin */ select t1.id,t1.name,t2.id id2,t2.name,t2.parent_id from t1,t2 where t1.id = t2.parent_id 05/04 17:21:11.447 DEBUG [$_NIOREACTOR-0-RW] (EnchachePool.java:76) -SQLRouteCache miss cache ,key:TESTDB/*!mycat:catlet=demo.catlets.ShareJoin */ select t1.id,t1.name,t2.id id2,t2.name,t2.parent_id from t1,t2 where t1.id = t2.parent_id 05/04 17:21:11.469 DEBUG [$_NIOREACTOR-0-RW] (HintCatletHandler.java:46) -load catelet class:demo.catlets.ShareJoin to run sql select t1.id,t1.name,t2.id id2,t2.name,t2.parent_id from t1,t2 where t1.id = t2.parent_id 05/04 17:21:11.573 INFO [$_NIOREACTOR-0-RW] (JoinParser.java:70) -SQL: select t1.id,t1.name,t2.id id2,t2.name,t2.parent_id from t1,t2 where t1.id = t2.parent_id # 这里路由正确，catlet路由到了dn1、dn2了。 05/04 17:21:11.677 INFO [$_NIOREACTOR-0-RW] (ShareJoin.java:150) -Catlet exec:dn1,dn2, sql:select id , name from t1 05/04 17:21:11.677 DEBUG [BusinessExecutor2] (PhysicalDBPool.java:452) -select read source hostM1 for dataHost:dh1 05/04 17:21:11.681 DEBUG [BusinessExecutor2] (SQLJob.java:85) -con query sql:select id , name from t1 to con:MySQLConnection [id=2, lastTime=1462353671681, user=root, schema=db1, old shema=db1, borrowed=true, fromSlaveDB=false, threadId=103614, charset=utf8, txIsolation=0, autocommit=true, attachment=dn1{select id , name from t1}, respHandler=null, host=192.168.121.61, port=3306, statusSync=null, writeQueue=0, modifiedSQLExecuted=false] 05/04 17:21:11.685 DEBUG [$_NIOREACTOR-0-RW] (PhysicalDatasource.java:403) -release channel MySQLConnection [id=2, lastTime=1462353671666, user=root, schema=db1, old shema=db1, borrowed=true, fromSlaveDB=false, threadId=103614, charset=utf8, txIsolation=0, autocommit=true, attachment=null, respHandler=null, host=192.168.121.61, port=3306, statusSync=null, writeQueue=0, modifiedSQLExecuted=false] 05/04 17:21:11.685 INFO [$_NIOREACTOR-0-RW] (BatchSQLJob.java:41) -job finished SQLJob [ id=1,dataNodeOrDatabase=dn1,sql=select id , name from t1, jobHandler=demo.catlets.ShareDBJoinHandler@6fb40e2d] 05/04 17:21:11.685 DEBUG [BusinessExecutor0] (PhysicalDBPool.java:452) -select read source hostM1 for dataHost:dh1 05/04 17:21:11.686 DEBUG [BusinessExecutor0] (SQLJob.java:85) -con query sql:select id , name from t1 to con:MySQLConnection [id=8, lastTime=1462353671686, user=root, schema=db2, old shema=db2, borrowed=true, fromSlaveDB=false, threadId=103617, charset=utf8, txIsolation=0, autocommit=true, attachment=dn2{select id , name from t1}, respHandler=null, host=192.168.121.61, port=3306, statusSync=null, writeQueue=0, modifiedSQLExecuted=false] 05/04 17:21:11.687 DEBUG [$_NIOREACTOR-0-RW] (PhysicalDatasource.java:403) -release channel MySQLConnection [id=8, lastTime=1462353671666, user=root, schema=db2, old shema=db2, borrowed=true, fromSlaveDB=false, threadId=103617, charset=utf8, txIsolation=0, autocommit=true, attachment=null, respHandler=null, host=192.168.121.61, port=3306, statusSync=null, writeQueue=0, modifiedSQLExecuted=false] 05/04 17:21:11.724 DEBUG [BusinessExecutor1] (PhysicalDBPool.java:452) -select read source hostM1 for dataHost:dh1 # 这里面有用到SQLJob.java，通过将t1表的id传给t2表以where in(1,2)的方式来获取t2表的数据 05/04 17:21:11.724 DEBUG [BusinessExecutor1] (SQLJob.java:85) -con query sql:select parent_id, id as id2 , name , parent_id from t2 where parent_id in (1,2) to con:MySQLConnection [id=2, lastTime=1462353671724, user=root, schema=db1, old shema=db1, borrowed=true, fromSlaveDB=false, threadId=103614, charset=utf8, txIsolation=0, autocommit=true, attachment=dn1{select parent_id, id as id2 , name , parent_id from t2 where parent_id in (1,2) }, respHandler=null, host=192.168.121.61, port=3306, statusSync=null, writeQueue=0, modifiedSQLExecuted=false] 而在mycat中，执行这个sql语句是能获取到4条记录的，如下所示： mysql> select parent_id, id as id2 , name , parent_id from t2 where parent_id in (1,2); +-----------+-----+-------+-----------+ | parent_id | id2 | name | parent_id | +-----------+-----+-------+-----------+ | 1 | 1 | db1.2 | 1 | | 2 | 3 | db2.2 | 2 | | 1 | 2 | db1.1 | 1 | | 2 | 4 | db2.2 | 2 | +-----------+-----+-------+-----------+ 4 rows in set (0.03 sec) mysql> 那为什么最后在mycat窗口中显示为2条呢？继续看下面日志： 05/04 17:21:11.724 DEBUG [BusinessExecutor3] (PhysicalDBPool.java:452) -select read source hostM1 for dataHost:dh1 05/04 17:21:11.725 DEBUG [BusinessExecutor3] (SQLJob.java:85) -con query sql:select parent_id, id as id2 , name , parent_id from t2 where parent_id in (1,2) to con:MySQLConnection [id=8, lastTime=1462353671725, user=root, schema=db2, old shema=db2, borrowed=true, fromSlaveDB=false, threadId=103617, charset=utf8, txIsolation=0, autocommit=true, attachment=dn2{select parent_id, id as id2 , name , parent_id from t2 where parent_id in (1,2) }, respHandler=null, host=192.168.121.61, port=3306, statusSync=null, writeQueue=0, modifiedSQLExecuted=false] 05/04 17:21:11.725 INFO [$_NIOREACTOR-0-RW] (ShareJoin.java:229) -SQLParallJob:dn1,dn2, sql:select parent_id, id as id2 , name , parent_id from t2 where parent_id in (1,2) 05/04 17:21:11.726 INFO [$_NIOREACTOR-0-RW] (BatchSQLJob.java:41) -job finished SQLJob [ id=2,dataNodeOrDatabase=dn2,sql=select id , name from t1, jobHandler=demo.catlets.ShareDBJoinHandler@6fb40e2d] 05/04 17:21:11.726 DEBUG [$_NIOREACTOR-0-RW] (EngineCtx.java:82) -packge id 1 05/04 17:21:11.727 DEBUG [$_NIOREACTOR-0-RW] (PhysicalDatasource.java:403) -release channel MySQLConnection [id=2, lastTime=1462353671707, user=root, schema=db1, old shema=db1, borrowed=true, fromSlaveDB=false, threadId=103614, charset=utf8, txIsolation=0, autocommit=true, attachment=null, respHandler=null, host=192.168.121.61, port=3306, statusSync=null, writeQueue=0, modifiedSQLExecuted=false] 05/04 17:21:11.728 INFO [$_NIOREACTOR-0-RW] (BatchSQLJob.java:41) -job finished SQLJob [ id=3,dataNodeOrDatabase=dn1,sql=select parent_id, id as id2 , name , parent_id from t2 where parent_id in (1,2) , jobHandler=demo.catlets.ShareRowOutPutDataHandler@13037844] 05/04 17:21:11.728 DEBUG [$_NIOREACTOR-0-RW] (PhysicalDatasource.java:403) -release channel MySQLConnection [id=8, lastTime=1462353671707, user=root, schema=db2, old shema=db2, borrowed=true, fromSlaveDB=false, threadId=103617, charset=utf8, txIsolation=0, autocommit=true, attachment=null, respHandler=null, host=192.168.121.61, port=3306, statusSync=null, writeQueue=0, modifiedSQLExecuted=false] 05/04 17:21:11.728 INFO [$_NIOREACTOR-0-RW] (BatchSQLJob.java:41) -job finished SQLJob [ id=4,dataNodeOrDatabase=dn2,sql=select parent_id, id as id2 , name , parent_id from t2 where parent_id in (1,2) , jobHandler=demo.catlets.ShareRowOutPutDataHandler@13037844] 05/04 17:21:11.729 INFO [$_NIOREACTOR-0-RW] (EngineCtx.java:171) -all job finished for front connection: ServerConnection [id=1, schema=TESTDB, host=127.0.0.1, user=test,txIsolation=3, autocommit=true, schema=TESTDB] 05/04 17:21:11.729 INFO [$_NIOREACTOR-0-RW] (EngineCtx.java:159) -write eof ,packgId:10 05/04 17:21:11.729 INFO [$_NIOREACTOR-0-RW] (ShareJoin.java:159) -发送数据OK PS：看到最后，一切流程正常了，没有看到问题所在，看来只有去看源代码了。

6，源码分析join

01.png：



02.png：



如果说。两次都获取到了，就正常了：03.png：



那为啥2次获取不到呢？看着啊，我输出了点东西，04.png：



这就是原因：

private byte[] getRow(String value,int index){ for(Map.Entry<String,byte[]> e: arows.entrySet() ){ String key=e.getKey(); RowDataPacket rowDataPkg = ResultSetUtil.parseRowData(e.getValue(), afields); String id = ByteUtil.getString(rowDataPkg.fieldValues.get(index)); if (id.equals(value)){ System.out.println("getRow方法，结果集将A表join列值为【"+value+"】的集合remove掉了，再相查就查不到了"); return arows.remove(key); } } return null; } 这里面的逻辑，处理比较麻烦，如果想改，还没想好怎么改……

再次描述下，不知道是否能描述清楚，大家都懂的，it人在讲述“专业高深技能”方面经常是一剑西来天外飞仙，场面恢宏绚丽无比，口如悬河滔滔不绝，就是太高大上了，普通人叹为观止一时无法领悟其中精髓……
这个还是接地气点，说的是他第一查询后，把对应key的值remove掉了，所以第二次查不到了,他查B表是查到4条，根据B表查询结果，取原先A表查询结果去组合返回结果，一条一条返回，可以第一次查的时候把A表对应值的记录去掉了，第二条（关联列值相同）查不到A表记录，他认为不符合join结果，就去掉了。个人理解应该i是判断是否符合join条件，和removekey那个值，分开处理才是的。个人建议。

--<>--这个sharejoin处理的很复杂，如果不稳定的话，建议抛弃，ER也建议抛弃

Bty：此处问题有akey提出，我做了数据准备工作日志分析，帅哥做了源码分析工作，victor大神积极参与，静哥等密切关注推进，最后我整理交流记录而成本篇笔记，准备提交git，谢谢大家的帮助。