Failed to write to mysql.slow_log

最近将一MySQL数据库的系统变量log_output从file调整为table后，偶尔会收到告警邮件，告警邮件内容为：

Failed to write to mysql.slow_log。

查了一下这个问题，发现居然是一个Bug，其实出现这个错误是因为慢查询的SQL语句太长，导致插入mysql.slow_log系统表时超过字段的长度，所以在错误日志当中出现"Failed to write to mysql.slow_log"信息。官方文档的Bug信息为Bug #37132 Logging to slow_log table fails with very slow queries。^[1] 摘抄其中一段描述内容如下：

Logging to the mysql.slow_log system table could fail when values were to large for table columns. Now logging proceeds on a best-effort basis, writing what information can be provided. Otherwise, the row is discarded and a message is written to the error log.

这个Bug直到MySQL 8.0.17才被Fix掉，在这之前从未碰到过，第一次遇到也颇感意外，遇到了就记录一下！

参考资料