怎么理解MySQL中半同步引起Master实例Crash，很多新手对此不是很清楚，为了帮助大家解决这个难题，下面小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。
PS: 在测试的过程中, 多次执行了select语句, 然后确认主库的半同步状态也是ON的情况下迅速在从库上重启slave, 基本是必现的;
PPS: MyISAM表在open的时候会同时打开所有的分区文件, 所以能比较方便的模拟占用大量文件描述符的情景;
(MyISAM分区表: http://blog.itpub.net/29510932/viewspace-2134679/)
PPPPPPPS: _(:з」∠)_
附上测试用的脚本与Crash的信息
CREATE TABLE `myisam_t` (
`id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
/*!50100 PARTITION BY HASH (id)
PARTITIONS 2000 */
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2017-04-28T22:10:00.731611+08:00 5092 [Note] Start binlog_dump to master_thread_id(5092) slave_server(13043), pos(, 4)
2017-04-28T22:10:01.648365+08:00 5092 [Note] Start semi-sync binlog_dump to slave (server_id: 13043), pos(, 4)
*** buffer overflow detected ***: /usr/sbin/mysqld terminated
Backtrace:
/lib/x86_64-linux-gnu/libc.so.6(+0x731af)[0x7fcdfc7981af]
/lib/x86_64-linux-gnu/libc.so.6(__fortify_fail+0x37)[0x7fcdfc81dcf7]
/lib/x86_64-linux-gnu/libc.so.6(+0xf6f10)[0x7fcdfc81bf10]
/lib/x86_64-linux-gnu/libc.so.6(+0xf8c67)[0x7fcdfc81dc67]
/usr/lib/mysql/plugin/semisync_master.so(_ZN12Ack_receiver17get_slave_socketsEP6fd_set+0x83)[0x7fcc73d4a493]
/usr/lib/mysql/plugin/semisync_master.so(_ZN12Ack_receiver3runEv+0x603)[0x7fcc73d4aaf3]
/usr/lib/mysql/plugin/semisync_master.so(ack_receive_handler+0x19)[0x7fcc73d4aba9]
/usr/sbin/mysqld(pfs_spawn_thread+0x1b4)[0xe90784]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x80a4)[0x7fcdfdf650a4]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7fcdfc80d87d]
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14:10:01 UTC - mysqld got signal 6 ;
This could be because you hit a bug. It is also possible that this binary
or one of the libraries it was linked against is corrupt, improperly built,
or misconfigured. This error can also be caused by malfunctioning hardware.
Attempting to collect some information that could help diagnose the problem.
As this is a crash and something is definitely wrong, the information
collection process might fail.
key_buffer_size=8388608
read_buffer_size=131072
max_used_connections=5
max_threads=9999
thread_count=8
connection_count=2
It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 21899362 K bytes of memory
Hope that's ok; if not, decrease some variables in the equation.
Thread pointer: 0x0
Attempting backtrace. You can use the following information to find out
where mysqld died. If you see no messages after this, something went
terribly wrong...
stack_bottom = 0 thread_stack 0x40000
/usr/sbin/mysqld(my_print_stacktrace+0x2c)[0xe77fec]
/usr/sbin/mysqld(handle_fatal_signal+0x459)[0x7a7019]
/lib/x86_64-linux-gnu/libpthread.so.0(+0xf8d0)[0x7fcdfdf6c8d0]
/lib/x86_64-linux-gnu/libc.so.6(gsignal+0x37)[0x7fcdfc75a067]
/lib/x86_64-linux-gnu/libc.so.6(abort+0x148)[0x7fcdfc75b448]
/lib/x86_64-linux-gnu/libc.so.6(+0x731b4)[0x7fcdfc7981b4]
/lib/x86_64-linux-gnu/libc.so.6(__fortify_fail+0x37)[0x7fcdfc81dcf7]
/lib/x86_64-linux-gnu/libc.so.6(+0xf6f10)[0x7fcdfc81bf10]
/lib/x86_64-linux-gnu/libc.so.6(+0xf8c67)[0x7fcdfc81dc67]
/usr/lib/mysql/plugin/semisync_master.so(_ZN12Ack_receiver17get_slave_socketsEP6fd_set+0x83)[0x7fcc73d4a493]
/usr/lib/mysql/plugin/semisync_master.so(_ZN12Ack_receiver3runEv+0x603)[0x7fcc73d4aaf3]
/usr/lib/mysql/plugin/semisync_master.so(ack_receive_handler+0x19)[0x7fcc73d4aba9]
/usr/sbin/mysqld(pfs_spawn_thread+0x1b4)[0xe90784]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x80a4)[0x7fcdfdf650a4]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7fcdfc80d87d]
The manual page at http://dev.mysql.com/doc/mysql/en/crashing.html contains
information that should help you find out what is causing the crash.
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