前言
近期，测试环境出现了一次MySQL数据库不断自动重启的问题，导致的原因是强行kill -9 杀掉数据库进程导致，报错信息如下：
2019-07-24T01:14:53.769512Z 0 [Note] Executing 'SELECT * FROM INFORMATION_SCHEMA.TABLES;' to get a list of tables using the deprecated partition engine. You may use the startup option '--disable-partition-engine-check' to skip this check.
2019-07-24T01:14:53.769516Z 0 [Note] Beginning of list of non-natively partitioned tables
01:14:53 UTC - mysqld got signal 11 ;
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.
Please help us make Percona Server better by reporting any
bugs at http://bugs.percona.com/key_buffer_size=33554432
read_buffer_size=8388608
max_used_connections=0
max_threads=501
thread_count=4
connection_count=0
It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 4478400 K bytes of memory
Hope that's ok; if not, decrease some variables in the equation.Thread pointer: 0x7f486900e000
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 = 7f4846172820 thread_stack 0x80000
/usr/local/mysql5.7/bin/mysqld(my_print_stacktrace+0x2c)[0xed481c]
/usr/local/mysql5.7/bin/mysqld(handle_fatal_signal+0x461)[0x7a15a1]
/lib64/libpthread.so.0(+0xf7e0)[0x7f498697c7e0]
/usr/local/mysql5.7/bin/mysqld(_ZN12ha_federated7rnd_posEPhS0_+0x2f)[0x12bcc3f]
/usr/local/mysql5.7/bin/mysqld(_ZN7handler10ha_rnd_posEPhS0_+0x172)[0x804a12]
/usr/local/mysql5.7/bin/mysqld(_ZN14Rows_log_event24do_index_scan_and_updateEPK14Relay_log_info+0x1e3)[0xe50e23]
/usr/local/mysql5.7/bin/mysqld(_ZN14Rows_log_event14do_apply_eventEPK14Relay_log_info+0x716)[0xe50196]
/usr/local/mysql5.7/bin/mysqld(_ZN9Log_event11apply_eventEP14Relay_log_info+0x6e)[0xe48fde]
/usr/local/mysql5.7/bin/mysqld(_Z26apply_event_and_update_posPP9Log_eventP3THDP14Relay_log_info+0x1f0)[0xe8d6f0]
/usr/local/mysql5.7/bin/mysqld(handle_slave_sql+0x163d)[0xe9a0fd]
/usr/local/mysql5.7/bin/mysqld(pfs_spawn_thread+0x1b4)[0x1209414]
/lib64/libpthread.so.0(+0x7aa1)[0x7f4986974aa1]
/lib64/libc.so.6(clone+0x6d)[0x7f4984c6bc4d]Trying to get some variables.
Some pointers may be invalid and cause the dump to abort.
Query (0): is an invalid pointer
Connection ID (thread ID): 2
Status: NOT_KILLEDYou may download the Percona Server operations manual by visiting
http://www.percona.com/software/percona-server/. You may find information
in the manual which will help you identify the cause of the crash.
1. 初探过程
之前出现过类似的情况时，是因为内存不足，因日志中也有对应的提示：
key_buffer_size=33554432 read_buffer_size=8388608 max_used_connections=0 max_threads=501 thread_count=4 connection_count=0 It is possible that mysqld could use up to key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 4478400 K bytes of memory Hope that's ok; if not, decrease some variables in the equation.
此测试环境物理内存确实不大，且剩余内存也不足，而且是作为另一个测试环境的从库，内存分配的也少。
之前一些环境也出现过类似的情况，通过调整参数及释放内存的等处理后可以正常启动，于是尝试着关闭一些临时程序并调整MySQL上述几个参数的值，如：
[mysqld] max_connections = 50
然后重新启动MySQL，结果依旧不断重启。
初步处理未果。
2. 添加innodb_force_recovery 解决不断重启
在配置文件my.cnf添加innodb_force_recovery 先处理不断重启的问题
[mysqld] innodb_force_recovery = 4
添加后，再次启动MySQL，此时不再出现反复重启。
查看数据库日志，有提示 [Note] InnoDB: !!! innodb_force_recovery is set to 4 !!!如下：
因为此时可以打开数据库，于是尝试启动从库，但是此时报错，提示Table 'mysql.slave_relay_log_info' is read only.
此时再看错误日志，如下
因此，本次启动时，innodb_force_recovery 设置为 4，在MySQL 5.6.15 以后，当 innodb_force_recovery 的值大于等于 4 的时候，InnoDB 表处于只读模式，因启动复制时需要将信息写入表中，所以此时报错。
注： 因设置为1-3 时，依旧未生效，因此我在处理时设置的为4（4 以上的值可能永久导致数据文件损坏。如果生产环境出现类似问题务必先拷贝一份测试，在测试通过后再在生产环境处理）。此时可以将所有数据dump出，之后再恢复即可。
3. innodb_force_recovery 参数
innodb_force_recovery 可以设置为 1-6，大的值包含前面所有小于它的值的影响。
1 (SRV_FORCE_IGNORE_CORRUPT): 忽略检查到的 corrupt 页。尽管检测到了损坏的 page 仍强制服务运行。一般设置为该值即可，然后 dump 出库表进行重建。
2 (SRV_FORCE_NO_BACKGROUND): 阻止主线程的运行，如主线程需要执行 full purge 操作，会导致 crash。 阻止 master thread 和任何 purge thread 运行。若 crash 发生在 purge 环节则使用该值。
3 (SRV_FORCE_NO_TRX_UNDO): 不执行事务回滚操作。
4 (SRV_FORCE_NO_IBUF_MERGE): 不执行插入缓冲的合并操作。如果可能导致崩溃则不要做这些操作。不要进行统计操作。该值可能永久损坏数据文件。若使用了该值，则将来要删除和重建辅助索引。
5 (SRV_FORCE_NO_UNDO_LOG_SCAN): 不查看重做日志，InnoDB 存储引擎会将未提交的事务视为已提交。此时 InnoDB 甚至把未完成的事务按照提交处理。该值可能永久性的损坏数据文件。
6 (SRV_FORCE_NO_LOG_REDO): 不执行前滚的操作。恢复时不做 redo log roll-forward。使数据库页处于废止状态，继而可能引起 B 树或者其他数据库结构更多的损坏。
注意：
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