MySQL错误日志文件突然暴涨的原因
1. 现象
今天协助其他同学排查问题的时候，发现数据库错误日志文件已经有9G以上了，打开内容查看如下：
=====================================
2020-07-08 13:47:43 0x7fe3723ff700 INNODB MONITOR OUTPUT
=====================================
Per second averages calculated from the last 1 seconds
-----------------
BACKGROUND THREAD
-----------------
srv_master_thread loops: 28112548 srv_active, 0 srv_shutdown, 18948137 srv_idle
srv_master_thread log flush and writes: 47060685
----------
SEMAPHORES
----------
OS WAIT ARRAY INFO: reservation count 213360683
OS WAIT ARRAY INFO: reservation count 218012898
OS WAIT ARRAY INFO: reservation count 218624956
OS WAIT ARRAY INFO: reservation count 223392430
OS WAIT ARRAY INFO: reservation count 213358783
OS WAIT ARRAY INFO: reservation count 217996917
OS WAIT ARRAY INFO: reservation count 218627068
OS WAIT ARRAY INFO: reservation count 223399094
OS WAIT ARRAY INFO: reservation count 213372264
OS WAIT ARRAY INFO: reservation count 217974752
OS WAIT ARRAY INFO: reservation count 218606657
OS WAIT ARRAY INFO: reservation count 223387430
OS WAIT ARRAY INFO: reservation count 213382268
OS WAIT ARRAY INFO: reservation count 218029924
OS WAIT ARRAY INFO: reservation count 218619464
OS WAIT ARRAY INFO: reservation count 223399870
OS WAIT ARRAY INFO: signal count 2558329753
RW-shared spins 0, rounds 2208700138, OS waits 822920663
RW-excl spins 0, rounds 80631903713, OS waits 1603642807
RW-sx spins 1202513351, rounds 33533328545, OS waits 959708531
Spin rounds per wait: 2208700138.00 RW-shared, 80631903713.00 RW-excl, 27.89 RW-sx
------------------------
LATEST DETECTED DEADLOCK
------------------------
2020-04-21 19:50:05 0x7fe28a7fd700
...
...
...
Process ID=54642, Main thread ID=140614440048384, state: sleeping
Number of rows inserted 5475421722, updated 433989820, deleted 4122238559, read 669572614313
708.29 inserts/s, 34.97 updates/s, 573.43 deletes/s, 29898.10 reads/s
----------------------------
END OF INNODB MONITOR OUTPUT
============================
此内容是InnoDB MONITOR的结果（和show engine innodb status结果一样），也就是说开启了InnoDB监视器。而且每15s刷新一次，导致日志文件的增速较快。
InnoDB MONITOR主要涉及的参数有innodb_status_output 和 innodb_status_output_locks ，这两个系统变量是用来启用标准innodb监控和 InnoDB锁监控的，查看本实例参数情况：
mysql> show global variables like '%innodb_status%';
+----------------------------+-------+
| Variable_name | Value |
+----------------------------+-------+
| innodb_status_output | ON |
| innodb_status_output_locks | ON |
+----------------------------+-------+
2 rows in set (0.01 sec)
说明确实已经开启了。
2. 关闭INNODB MONITOR
可以在线关闭INNODB MONITOR，但是在关闭前建议先将原日志备份（重命名）
mv mysqld.log mysqld.log.20200708
再修改参数，关闭监控
mysql> set global innodb_status_output='OFF';
Query OK, 0 rows affected (0.00 sec)
mysql> set global innodb_status_output_locks='OFF';
Query OK, 0 rows affected (0.00 sec)
mysql> flush logs;
时间有限，今天暂时就简单说明现象及引起日志暴涨的原因，后续有机会在关注日志内容及相关参数意义。
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7. MySQL敏感数据加密及解密
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9. MySQL数据备份及还原（二）
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