MySQL：网络断开后执行的事务怎么处理(read_timeout/write_timeout))

水平有限，可能有误

一、read_timeout/write_timeout参数实现

另外一篇关于wait_timeout的文章
MySQL：参数wait_timeout和interactive_timeout以及空闲超时的实现

MySQL普通的链接没有保活机制，即没有设置socket属性，也没有设置心跳。如果网络链接断开不能及时服务端不能及时探测到。默认TCP 2小时+11次*75秒。

连接使用这种方式进行：
socket->listen->poll(socketfd)->accept->newthread->poll(newfd,wait_timeout)
一旦有新的数据到来，如果需要读取或者写入由于网络问题依旧使用poll进行等待，直到超时。
其中参数read_timeout/write_timeout用于读取网络数据的，如果网络不可用能够等待网络可用的时间，也就是wait_timeout和read_timeout/write_timeou均使用poll的timeout实现。见栈2，可见vio_io_wait函数用于处理各种超时，主要用poll来处理。

net_write_packet
 ->net_write_raw_loop  一个包大小16M
  ->vio_write
    ->mysql_socket_send 如果发送信息失败 inline_mysql_socket_send调用send命令
    ->如果是SOCKET_EAGAIN那么通过vio_socket_io_wait函数进行判定，需要等待的时间
      /* Wait for the output buffer to become writable.*/

二、事务在网络断开后如何处理

测试方法很简单，做一个表16384行，然后使用

begin; 
insert into table select * from table limit 10; 
select sleep(0.01),* from table ;

执行期间断开客户端网卡连接，在服务端依旧可以看到

mysql> show processlist;
+----+-------+--------------------+------+---------+------+------------+-------------------------------------+-----------+---------------+
| Id | User  | Host               | db   | Command | Time | State      | Info                                | Rows_sent | Rows_examined |
+----+-------+--------------------+------+---------+------+------------+-------------------------------------+-----------+---------------+
|  7 | root  | localhost          | NULL | Query   |    0 | starting   | show processlist                    |         0 |             0 |
| 10 | ptest | 192.168.1.61:34540 | NULL | Query   |  258 | User sleep | select *,sleep(0.01) from test.oooo |      6651 |             0 |
+----+-------+--------------------+------+---------+------+------------+-------------------------------------+-----------+---------------+

直到write timeout时间后可以看到rollback栈。

一个连接进行事务后，如果事务语句正在执行，那么网络断开后会在语句执行完成后回滚掉。因为执行状态包不能送达客户端,因此会感知到这种网络断开的错误。

    if (thd->is_error() || (thd->variables.option_bits & OPTION_MASTER_SQL_ERROR))
      trans_rollback_stmt(thd);

一个连接进行事务后，如果事务执行完成而没有提交，如果网络断开，那么事务还存在语服务端，需要手动kill。因为默认会在2小时+11次*75秒后断开回滚。

[root@localhost ~]# netstat -anlp|grep 192.168.1.61
tcp6       0      0 192.168.1.62:3306       192.168.1.61:36926      ESTABLISHED 40913/mysqld

栈1：回滚栈

(gdb) bt
#0  innobase_rollback (hton=0x2e12440, thd=0x7ffefc000950, rollback_trx=false) at /home/mysql/soft/percona-server-5.7.29-32/storage/innobase/handler/ha_innodb.cc:5452
#1  0x0000000000ea6ab8 in ha_rollback_low (thd=0x7ffefc000950, all=false) at /home/mysql/soft/percona-server-5.7.29-32/sql/handler.cc:2019
#2  0x00000000017f0f23 in MYSQL_BIN_LOG::rollback (this=0x2d668a0 <mysql_bin_log>, thd=0x7ffefc000950, all=false) at /home/mysql/soft/percona-server-5.7.29-32/sql/binlog.cc:2532
#3  0x0000000000ea6d40 in ha_rollback_trans (thd=0x7ffefc000950, all=false) at /home/mysql/soft/percona-server-5.7.29-32/sql/handler.cc:2106
#4  0x00000000015c6a13 in trans_rollback_stmt (thd=0x7ffefc000950) at /home/mysql/soft/percona-server-5.7.29-32/sql/transaction.cc:515
#5  0x00000000014c08de in mysql_execute_command (thd=0x7ffefc000950, first_level=true) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_parse.cc:5325
#6  0x00000000014c2025 in mysql_parse (thd=0x7ffefc000950, parser_state=0x7fffe88824a0, update_userstat=false) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_parse.cc:5927
#7  0x00000000014b6c5f in dispatch_command (thd=0x7ffefc000950, com_data=0x7fffe8882c90, command=COM_QUERY) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_parse.cc:1539
#8  0x00000000014b5a94 in do_command (thd=0x7ffefc000950) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_parse.cc:1060
#9  0x00000000015e9d32 in handle_connection (arg=0x3c09eb0) at /home/mysql/soft/percona-server-5.7.29-32/sql/conn_handler/connection_handler_per_thread.cc:325
#10 0x00000000018b97f2 in pfs_spawn_thread (arg=0x3b784b0) at /home/mysql/soft/percona-server-5.7.29-32/storage/perfschema/pfs.cc:2198
#11 0x00007ffff7bc6ea5 in start_thread () from /lib64/libpthread.so.0
#12 0x00007ffff5fa08dd in clone () from /lib64/libc.so.6

栈2 写入等待timeout=60000 即默认的write_timeout=60S

#0  0x00007ffff5f95c3d in poll () from /lib64/libc.so.6
#1  0x0000000001da0e3b in vio_io_wait (vio=0x7ffefc005690, event=VIO_IO_EVENT_WRITE, timeout=60000) at /home/mysql/soft/percona-server-5.7.29-32/vio/viosocket.c:1173
#2  0x0000000001d9f352 in vio_socket_io_wait (vio=0x7ffefc005690, event=VIO_IO_EVENT_WRITE) at /home/mysql/soft/percona-server-5.7.29-32/vio/viosocket.c:127
#3  0x0000000001d9f74a in vio_write (vio=0x7ffefc005690, buf=0x7ffefc013838 "\001\061\001\060\004", size=12872) at /home/mysql/soft/percona-server-5.7.29-32/vio/viosocket.c:260
#4  0x00000000016f92a3 in net_write_raw_loop (net=0x7ffefc002528, buf=0x7ffefc013838 "\001\061\001\060\004", count=12872) at /home/mysql/soft/percona-server-5.7.29-32/sql/net_serv.cc:522
#5  0x00000000016f9588 in net_write_packet (net=0x7ffefc002528, packet=0x7ffefc012a80 "\001\061\001\060\004", length=16384) at /home/mysql/soft/percona-server-5.7.29-32/sql/net_serv.cc:661
#6  0x00000000016f9177 in net_write_buff (net=0x7ffefc002528, packet=0x7ffefc936f70 "\001\061\001\060", len=4) at /home/mysql/soft/percona-server-5.7.29-32/sql/net_serv.cc:474
#7  0x00000000016f8e1c in my_net_write (net=0x7ffefc002528, packet=0x7ffefc936f70 "\001\061\001\060", len=4) at /home/mysql/soft/percona-server-5.7.29-32/sql/net_serv.cc:347
#8  0x0000000001745635 in Protocol_classic::end_row (this=0x7ffefc001c68) at /home/mysql/soft/percona-server-5.7.29-32/sql/protocol_classic.cc:1204
#9  0x00000000014571d7 in Query_result_send::send_data (this=0x7ffefc0097a0, items=...) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_class.cc:2937
#10 0x0000000001477a0d in end_send (join=0x7ffefc009a70, qep_tab=0x7ffefc93b290, end_of_records=false) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_executor.cc:2946
#11 0x000000000147461b in evaluate_join_record (join=0x7ffefc009a70, qep_tab=0x7ffefc93b118) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_executor.cc:1652
#12 0x0000000001473a5b in sub_select (join=0x7ffefc009a70, qep_tab=0x7ffefc93b118, end_of_records=false) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_executor.cc:1304
#13 0x00000000014732dc in do_select (join=0x7ffefc009a70) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_executor.cc:957
#14 0x0000000001471243 in JOIN::exec (this=0x7ffefc009a70) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_executor.cc:206
#15 0x000000000150d2d5 in handle_query (thd=0x7ffefc000950, lex=0x7ffefc003000, result=0x7ffefc0097a0, added_options=0, removed_options=0)
    at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_select.cc:192
#16 0x00000000014c1097 in execute_sqlcom_select (thd=0x7ffefc000950, all_tables=0x7ffefc009160) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_parse.cc:5490
#17 0x00000000014ba323 in mysql_execute_command (thd=0x7ffefc000950, first_level=true) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_parse.cc:3016
#18 0x00000000014c2025 in mysql_parse (thd=0x7ffefc000950, parser_state=0x7fffe88824a0, update_userstat=false) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_parse.cc:5927
#19 0x00000000014b6c5f in dispatch_command (thd=0x7ffefc000950, com_data=0x7fffe8882c90, command=COM_QUERY) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_parse.cc:1539
#20 0x00000000014b5a94 in do_command (thd=0x7ffefc000950) at /home/mysql/soft/percona-server-5.7.29-32/sql/sql_parse.cc:1060
#21 0x00000000015e9d32 in handle_connection (arg=0x3c09eb0) at /home/mysql/soft/percona-server-5.7.29-32/sql/conn_handler/connection_handler_per_thread.cc:325
#22 0x00000000018b97f2 in pfs_spawn_thread (arg=0x3b784b0) at /home/mysql/soft/percona-server-5.7.29-32/storage/perfschema/pfs.cc:2198
#23 0x00007ffff7bc6ea5 in start_thread () from /lib64/libpthread.so.0
#24 0x00007ffff5fa08dd in clone () from /lib64/libc.so.6
(gdb)