导读
一文快速掌握 MySQL进程号、连接ID、查询ID、InnoDB线程与系统线程的对应关系。
有时候，怀疑某个MySQL内存查询导致CPU或磁盘I/O消耗特别高，但又不确定具体是哪个SQL引起的。
或者当InnoDB引擎内部有semaphore wait时，想知道具体是哪个线程/查询引起的。多说一下，当有semaphore wait事件超过600秒的话，InnoDB会发出crash信号：
InnoDB: ###### Diagnostic info printed to the standard error stream
2020-12-13T09:41:33.810011Z 0 [ERROR] [FATAL] InnoDB: Semaphore wait has lasted > 600 seconds. We intentionally crash the server because it appears to be hung.
2020-12-13 10:41:33 0x7f3d92a4e700 InnoDB: Assertion failure in thread 139902430013184 in file ut0ut.cc line 917
InnoDB: We intentionally generate a memory trap.
InnoDB: Submit a detailed bug report to http://bugs.mysql.com.
InnoDB: If you get repeated assertion failures or crashes, even
InnoDB: immediately after the mysqld startup, there may be
InnoDB: corruption in the InnoDB tablespace. Please refer to
InnoDB: http://dev.mysql.com/doc/refman/8.0/en/forcing-innodb-recovery.html
InnoDB: about forcing recovery.
09:41:33 UTC - mysqld got signal 6 ;
因此也要监控InnoDB的semaphore wait状态，一旦超过阈值，就要尽快报警并分析出问题原因，及时杀掉或停止引起等待的查询请求。
不过本文想讨论的是，MySQL的进程ID、内部查询ID、内部线程ID，和操作系统层的进程ID、线程如何对应起来。
