MySQL 8.0 重新定义了错误日志输出和过滤，改善了原来臃肿并且可读性很差的错误日志。
比如增加了 JSON 输出，在原来的日志后面以序号以及 JSON 后缀的方式展示。
比如我机器上的 MySQL 以 JSON 保存的错误日志 mysqld.log.00.json：
[root@centos-ytt80 mysql80]# jq . mysqld.log.00.json{ "log_type": 1, "prio": 1, "err_code": 12592, "subsystem": "InnoDB", "msg": "Operating system error number 2 in a file operation.", "time": "2019-09-03T08:16:12.111808Z", "thread": 8, "err_symbol": "ER_IB_MSG_767", "SQL_state": "HY000", "label": "Error"}{ "log_type": 1, "prio": 1, "err_code": 12593, "subsystem": "InnoDB", "msg": "The error means the system cannot find the path specified.", "time": "2019-09-03T08:16:12.111915Z", "thread": 8, "err_symbol": "ER_IB_MSG_768", "SQL_state": "HY000", "label": "Error"}{ "log_type": 1, "prio": 1, "err_code": 12216, "subsystem": "InnoDB", "msg": "Cannot open datafile for read-only: './ytt2/a.ibd' OS error: 71", "time": "2019-09-03T08:16:12.111933Z", "thread": 8, "err_symbol": "ER_IB_MSG_391", "SQL_state": "HY000", "label": "Error"}以 JSON 输出错误日志后可读性和可操作性增强了许多。这里可以用 Linux 命令 jq 或者把这个字串 COPY 到其他解析 JSON 的工具方便处理。
只想非常快速的拿出错误信息，忽略其他信息。
[root@centos-ytt80 mysql80]# jq '.msg' mysqld.log.00.json"Operating system error number 2 in a file operation.""The error means the system cannot find the path specified.""Cannot open datafile for read-only: './ytt2/a.ibd' OS error: 71""Cannot calculate statistics for table `ytt2`.`a` because the .ibd file is missing. Please refer to http://dev.mysql.com/doc/refman/8.0/en/innodb-troubleshooting.html for how to resolve the issue.""Cannot calculate statistics for table `ytt2`.`a` because the .ibd file is missing. Please refer to http://dev.mysql.com/doc/refman/8.0/en/innodb-troubleshooting.html for how to resolve the issue."使用 JSON 输出的前提是安装 JSON 输出部件。
INSTALL COMPONENT 'file://component_log_sink_json';完了在设置变量 SET GLOBAL log_error_services = 'log_filter_internal; log_sink_json';格式为：过滤规则；日志输出；[过滤规则]日志输出；
查看安装好的部件
mysql> select * from mysql.component;+--------------+--------------------+---------------------------------------+| component_id | component_group_id | component_urn |+--------------+--------------------+---------------------------------------+| 2 | 1 | file://component_log_sink_json |+--------------+--------------------+---------------------------------------+3 rows in set (0.00 sec)现在设置 JSON 输出，输出到系统日志的同时输出到 JSON 格式日志。
mysql> SET persist log_error_services = 'log_filter_internal; log_sink_internal; log_sink_json';Query OK, 0 rows affected (0.00 sec)来测试一把。我之前已经把表 a 物理文件删掉了。
mysql> select * from a;ERROR 1812 (HY000): Tablespace is missing for table `ytt2`.`a`.现在错误日志里有 5 条记录。
[root@centos-ytt80 mysql80]# tailf mysqld.log2019-09-03T08:16:12.111808Z 8 [ERROR] [MY-012592] [InnoDB] Operating system error number 2 in a file operation.2019-09-03T08:16:12.111915Z 8 [ERROR] [MY-012593] [InnoDB] The error means the system cannot find the path specified.2019-09-03T08:16:12.111933Z 8 [ERROR] [MY-012216] [InnoDB] Cannot open datafile for read-only: './ytt2/a.ibd' OS error: 712019-09-03T08:16:12.112227Z 8 [Warning] [MY-012049] [InnoDB] Cannot calculate statistics for table `ytt2`.`a` because the .ibd file is missing. Please refer to http://dev.mysql.com/doc/refman/8.0/en/innodb-troubleshooting.html for how to resolve the issue.2019-09-03T08:16:14.902617Z 8 [Warning] [MY-012049] [InnoDB] Cannot calculate statistics for table `ytt2`.`a` because the .ibd file is missing. Please refer to http://dev.mysql.com/doc/refman/8.0/en/innodb-troubleshooting.html for how to resolve the issue.JSON 日志里也有 5 条记录。
[root@centos-ytt80 mysql80]# tailf mysqld.log.00.json{ "log_type" : 1, "prio" : 1, "err_code" : 12592, "subsystem" : "InnoDB", "msg" : "Operating system error number 2 in a file operation.", "time" : "2019-09-03T08:16:12.111808Z", "thread" : 8, "err_symbol" : "ER_IB_MSG_767", "SQL_state" : "HY000", "label" : "Error" }{ "log_type" : 1, "prio" : 1, "err_code" : 12593, "subsystem" : "InnoDB", "msg" : "The error means the system cannot find the path specified.", "time" : "2019-09-03T08:16:12.111915Z", "thread" : 8, "err_symbol" : "ER_IB_MSG_768", "SQL_state" : "HY000", "label" : "Error" }{ "log_type" : 1, "prio" : 1, "err_code" : 12216, "subsystem" : "InnoDB", "msg" : "Cannot open datafile for read-only: './ytt2/a.ibd' OS error: 71", "time" : "2019-09-03T08:16:12.111933Z", "thread" : 8, "err_symbol" : "ER_IB_MSG_391", "SQL_state" : "HY000", "label" : "Error" }{ "log_type" : 1, "prio" : 2, "err_code" : 12049, "subsystem" : "InnoDB", "msg" : "Cannot calculate statistics for table `ytt2`.`a` because the .ibd file is missing. Please refer to http://dev.mysql.com/doc/refman/8.0/en/innodb-troubleshooting.html for how to resolve the issue.", "time" : "2019-09-03T08:16:12.112227Z", "thread" : 8, "err_symbol" : "ER_IB_MSG_224", "SQL_state" : "HY000", "label" : "Warning" }{ "log_type" : 1, "prio" : 2, "err_code" : 12049, "subsystem" : "InnoDB", "msg" : "Cannot calculate statistics for table `ytt2`.`a` because the .ibd file is missing. Please refer to http://dev.mysql.com/doc/refman/8.0/en/innodb-troubleshooting.html for how to resolve the issue.", "time" : "2019-09-03T08:16:14.902617Z", "thread" : 8, "err_symbol" : "ER_IB_MSG_224", "SQL_state" : "HY000", "label" : "Warning" }那可能有人就问了，这有啥意义呢？只是把格式变了，过滤的规则我看还是没变。
那我们现在给第二条日志输出加过滤规则
先把过滤日志的部件安装起来
INSTALL COMPONENT 'file://component_log_filter_dragnet';mysql> SET persist log_error_services = 'log_filter_internal; log_sink_internal; log_filter_dragnet;log_sink_json';Query OK, 0 rows affected (0.00 sec)只保留 error，其余的一律过滤掉。
SET GLOBAL dragnet.log_error_filter_rules = 'IF prio>=WARNING THEN drop.';检索一张误删的表
mysql> select * from a;ERROR 1812 (HY000): Tablespace is missing for table `ytt2`.`a`.查看错误日志和 JSON 错误日志
发现错误日志里有一条 Warning，JSON 错误日志里的被过滤掉了。
2019-09-03T08:22:32.978728Z 8 [Warning] [MY-012049] [InnoDB] Cannot calculate statistics for table `ytt2`.`a` because the .ibd file is missing. Please refer to http://dev.mysql.com/doc/refman/8.0/en/innodb-troubleshooting.html for how to resolve the issue.再举个例子，每 60 秒只允许记录一个 Warning 事件
mysql> SET GLOBAL dragnet.log_error_filter_rules = 'IF prio==WARNING THEN throttle 1/60.';Query OK, 0 rows affected (0.00 sec)多次执行
mysql> select * from b;ERROR 1812 (HY000): Tablespace is missing for table `ytt2`.`b`.mysql> select * from b;ERROR 1812 (HY000): Tablespace is missing for table `ytt2`.`b`.mysql> select * from b;ERROR 1812 (HY000): Tablespace is missing for table `ytt2`.`b`.现在错误日志里有三条 warning 信息
2019-09-03T08:49:06.820635Z 8 [Warning] [MY-012049] [InnoDB] Cannot calculate statistics for table `ytt2`.`b` because the .ibd file is missing. Please refer to http://dev.mysql.com/doc/refman/8.0/en/innodb-troubleshooting.html for how to resolve the issue.2019-09-03T08:49:31.455907Z 8 [Warning] [MY-012049] [InnoDB] Cannot calculate statistics for table `ytt2`.`b` because the .ibd file is missing. Please refer to http://dev.mysql.com/doc/refman/8.0/en/innodb-troubleshooting.html for how to resolve the issue.2019-09-03T08:50:00.430867Z 8 [Warning] [MY-012049] [InnoDB] Cannot calculate statistics for table `ytt2`.`b` because the .ibd file is missing. Please refer to http://dev.mysql.com/doc/refman/8.0/en/innodb-troubleshooting.html for how to resolve the issue.mysqld.log.00.json 只有一条
{ "log_type" : 1, "prio" : 2, "err_code" : 12049, "subsystem" : "InnoDB", "msg" : "Cannot calculate statistics for table `ytt2`.`b` because the .ibd file is missing. Please refer to http://dev.mysql.com/doc/refman/8.0/en/innodb-troubleshooting.html for how to resolve the issue.", "time" : "2019-09-03T08:49:06.820635Z", "thread" : 8, "err_symbol" : "ER_IB_MSG_224", "SQL_state" : "HY000", "and_n_more" : 3, "label" : "Warning" }总结，我这里简单介绍了下 MySQL 8.0 的错误日志过滤以及 JSON 输出。MySQL 8.0 的component_log_filter_dragnet 部件过滤规则非常灵活，可以参考手册，根据它提供的语法写出自己的过滤掉的日志输出。
