mysql复制和内存引擎的表

2024年3月23日 218次阅读来源: 河南-老宋(志强)

When a master server shuts down and restarts, its MEMORY tables become empty. To replicate this effect to slaves, the first time that the master uses a given MEMORY table after startup, it logs an event that notifies slaves that the table must to be emptied by writing a DELETE statement for that table to the binary log.

When a slave server shuts down and restarts, its MEMORY tables become empty. This causes the slave to be out of synchrony with the master and may lead to other failures or cause the slave to stop:

Row-format updates and deletes received from the master may fail with Can’t find record in ‘memory_table‘.
Statements such as INSERT INTO … SELECT FROM memory_table may insert a different set of rows on the master and slave.

当主库上使用内存引擎的表时，主库因为某些原因重启了。启动好之后，再打开主库的内存引擎表时，会先把里面的内容清空。所以这个时候主从状态是正常的。

但当从库被重启时，因为memory的内容没有了，所以可能会出现主从报错的现象。

实验：

一主库异常关闭：

在主库上建表

mysql> show create table b;

+-------+-------------------------------------------------------------------------------------------------------+

| Table | Create Table                                                                                          |

+-------+-------------------------------------------------------------------------------------------------------+

| b     | CREATE TABLE `b` (

  `id` int(11) NOT NULL,

  PRIMARY KEY (`id`)

) ENGINE=MEMORY DEFAULT CHARSET=utf8

主库：

mysql> insert into b values (10),(20);

Query OK, 2 rows affected (0.00 sec)

Records: 2  Duplicates: 0  Warnings: 0

从库：

mysql> select * from a.b;

+----+

| id |

+----+

| 10 |

| 20 |

+----+

重启主库后：

从库：

mysql> select * from a.b;

+----+

| id |

+----+

| 10 |

| 20 |

+----+

2 rows in set (0.00 sec)

这时再去主库上观察：

mysql> show master status;

+------------------+----------+--------------+------------------+-------------------------------------------+

| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set                         |

+------------------+----------+--------------+------------------+-------------------------------------------+

| mysql-bin.000012 |      194 |              |                  | 48dfe7f5-3ab5-11e7-b3fa-525400199b09:1-23 |

+------------------+----------+--------------+------------------+-------------------------------------------+

1 row in set (0.00 sec)



mysql> select  *from a.b;

Empty set (0.00 sec)



mysql> show master status;

+------------------+----------+--------------+------------------+-------------------------------------------+

| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set                         |

+------------------+----------+--------------+------------------+-------------------------------------------+

| mysql-bin.000012 |      478 |              |                  | 48dfe7f5-3ab5-11e7-b3fa-525400199b09:1-24 |

+------------------+----------+--------------+------------------+-------------------------------------------+

1 row in set (0.00 sec)



mysql> show binlog  events in 'mysql-bin.000012';

+------------------+-----+----------------+-----------+-------------+--------------------------------------------------------------------+

| Log_name         | Pos | Event_type     | Server_id | End_log_pos | Info                                                               |

+------------------+-----+----------------+-----------+-------------+--------------------------------------------------------------------+

| mysql-bin.000012 |   4 | Format_desc    | 169454186 |         123 | Server ver: 5.7.16.k1-ucloudrel1-log, Binlog ver: 4                |

| mysql-bin.000012 | 123 | Previous_gtids | 169454186 |         194 | 48dfe7f5-3ab5-11e7-b3fa-525400199b09:1-23                          |

| mysql-bin.000012 | 194 | Gtid           | 169454186 |         259 | SET @@SESSION.GTID_NEXT= '48dfe7f5-3ab5-11e7-b3fa-525400199b09:24' |

| mysql-bin.000012 | 259 | Query          | 169454186 |         327 | BEGIN                                                              |

| mysql-bin.000012 | 327 | Query          | 169454186 |         409 | DELETE FROM `a`.`b`                                                |

| mysql-bin.000012 | 409 | Query          | 169454186 |         478 | COMMIT                                                             |

+------------------+-----+----------------+-----------+-------------+--------------------------------------------------------------------+

6 rows in set (0.00 sec)

再次去从库观察：

mysql> select * from a.b;

Empty set (0.00 sec)

这时主从的状态也是正常的。

二从库异常重启：

主库上：

mysql> insert into a.b values (10),(20);

Query OK, 2 rows affected (0.00 sec)

Records: 2  Duplicates: 0  Warnings: 0

从库：

mysql> select * from a.b;

+----+

| id |

+----+

| 10 |

| 20 |

+----+

2 rows in set (0.00 sec)

重启从库后：

mysql> select  *from a.b;

Empty set (10.00 sec)

主库：

mysql> delete from a.b where id=10;

Query OK, 1 row affected (0.00 sec)

从库：

mysql> show slave status \G

*************************** 1. row ***************************

               Slave_IO_State: Waiting for master to send event

                  Master_Host: 10.25.170.106

                  Master_User: ucloudbackup

                  Master_Port: 3306

                Connect_Retry: 60

              Master_Log_File: mysql-bin.000012

          Read_Master_Log_Pos: 1049

               Relay_Log_File: mysql-relay.000024

                Relay_Log_Pos: 360

        Relay_Master_Log_File: mysql-bin.000012

             Slave_IO_Running: Yes

            Slave_SQL_Running: No

              Replicate_Do_DB:

          Replicate_Ignore_DB:

           Replicate_Do_Table:

       Replicate_Ignore_Table:

      Replicate_Wild_Do_Table:

  Replicate_Wild_Ignore_Table:

                   Last_Errno: 1032

                   Last_Error: Coordinator stopped because there were error(s) in the worker(s). The most recent failure being: Worker 0 failed executing transaction '48dfe7f5-3ab5-11e7-b3fa-525400199b09:26' at master log mysql-bin.000012, end_log_pos 980. See error log and/or performance_schema.replication_applier_status_by_worker table for more details about this failure or others, if any.

                 Skip_Counter: 0

分析：

重启主库，并且访问a.b表时， mysqlbinlog中会记录下面的内容：

# at 327

#170518 19:16:07 server id 10  end_log_pos 410 CRC32 0xc908da54 Query	thread_id=5	exec_time=499	error_code=0

SET TIMESTAMP=1495106167/*!*/;

DELETE FROM `a`.`b`

/*!*/;

通过跟踪可知：

#0  open_table_entry_fini (thd=0x7f3f1c000d80, share=0x7f3f14045b50, entry=0x7f3f1c00eef0) at /data/mysql-5.7.17/sql/sql_base.cc:4325

#1  0x00000000014968ac in open_table (thd=0x7f3f1c000d80, table_list=0x7f3f1c006580, ot_ctx=0x7f3f40092370) at /data/mysql-5.7.17/sql/sql_base.cc:3551

#2  0x000000000149912c in open_and_process_table (thd=0x7f3f1c000d80, lex=0x7f3f1c003078, tables=0x7f3f1c006580, counter=0x7f3f1c003138, flags=0, prelocking_strategy=0x7f3f40092470,

    has_prelocking_list=false, ot_ctx=0x7f3f40092370) at /data/mysql-5.7.17/sql/sql_base.cc:5108

#3  0x000000000149a1ce in open_tables (thd=0x7f3f1c000d80, start=0x7f3f40092430, counter=0x7f3f1c003138, flags=0, prelocking_strategy=0x7f3f40092470) at /data/mysql-5.7.17/sql/sql_base.cc:5719

#4  0x000000000149b4fb in open_tables_for_query (thd=0x7f3f1c000d80, tables=0x7f3f1c006580, flags=0) at /data/mysql-5.7.17/sql/sql_base.cc:6494

#5  0x00000000015208fe in execute_sqlcom_select (thd=0x7f3f1c000d80, all_tables=0x7f3f1c006580) at /data/mysql-5.7.17/sql/sql_parse.cc:5166

#6  0x000000000151a193 in mysql_execute_command (thd=0x7f3f1c000d80, first_level=true) at /data/mysql-5.7.17/sql/sql_parse.cc:2794

#7  0x00000000015218f6 in mysql_parse (thd=0x7f3f1c000d80, parser_state=0x7f3f40093690) at /data/mysql-5.7.17/sql/sql_parse.cc:5611

#8  0x000000000151709c in dispatch_command (thd=0x7f3f1c000d80, com_data=0x7f3f40093df0, command=COM_QUERY) at /data/mysql-5.7.17/sql/sql_parse.cc:1461

#9  0x0000000001515f8e in do_command (thd=0x7f3f1c000d80) at /data/mysql-5.7.17/sql/sql_parse.cc:999

#10 0x0000000001645460 in handle_connection (arg=0x43de0e0) at /data/mysql-5.7.17/sql/conn_handler/connection_handler_per_thread.cc:300

#11 0x0000000001cbe494 in pfs_spawn_thread (arg=0x4474250) at /data/mysql-5.7.17/storage/perfschema/pfs.cc:2188

#12 0x00007f3f4e629dc5 in start_thread () from /lib64/libpthread.so.0

#13 0x00007f3f4d4f473d in clone () from /lib64/libc.so.6

是在sql/sql_base.cc:open_table_entry_fini函数中实现的添加delete

具体是体现在：

 4345     if (mysql_bin_log.is_open())

 4346     {

 4347       bool error= false;

 4348       String temp_buf;

 4349       error= temp_buf.append("DELETE FROM ");

 4350       append_identifier(thd, &temp_buf, share->db.str, strlen(share->db.str));

 4351       error= temp_buf.append(".");

 4352       append_identifier(thd, &temp_buf, share->table_name.str,

 4353                         strlen(share->table_name.str));

 4354       if (mysql_bin_log.write_dml_directly(thd, temp_buf.c_ptr_safe(),

 4355                                            temp_buf.length()))

 4356         return TRUE;

 4357       if (error)

 4358       {

 4359         /*

 4360           As replication is maybe going to be corrupted, we need to warn the

 4361           DBA on top of warning the client (which will automatically be done

 4362           because of MYF(MY_WME) in my_malloc() above).

 4363         */

 4364         sql_print_error("When opening HEAP table, could not allocate memory "

 4365                         "to write 'DELETE FROM `%s`.`%s`' to the binary log",

 4366                         share->db.str, share->table_name.str);

 4367         delete entry->triggers;

 4368         return TRUE;

 4369       }

直接在mysqlbinlog中写了delete 语句。

对于有memory引擎的表，做主从时可能会有的问题：

1 逻辑备份：会dump出来当时memory表里有的内容，但他不支持事务，所以有可能数据是不一样的

2 物理备份：memory的表只有frm文件，所以里面的内容一定是空的

所以两种方式都不能保证可以直接做出来从库。

最好的方法是：在主从复制中还是不要使用memory引擎的表。真要用的话，需要了解他的影响。

声明：源码新手，仅代表个人意见，非权威，如果误导看官，见谅。

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    原文作者：河南-老宋(志强)
    原文地址: https://zhuanlan.zhihu.com/p/26985377
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