MySQL:终于为OS层面的线程命名了
能力有限，如果有误请谅解。
一、问题来源
最近在检查某个数据库性能的时候，通过top -Hu mysql看到了一个特别奇怪的现象，线程有了自己的名字，我开始以为是哪个大厂自己维护的版本，如下：
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
8146 mysql 20 0 4164720 734540 26624 S 0.0 9.9 0:00.96 mysqld
8159 mysql 20 0 4164720 734540 26624 S 0.0 9.9 0:00.02 ib_io_ibuf
8160 mysql 20 0 4164720 734540 26624 S 0.0 9.9 0:00.02 ib_io_log
8161 mysql 20 0 4164720 734540 26624 S 0.0 9.9 0:00.04 ib_io_rd-1
8162 mysql 20 0 4164720 734540 26624 S 0.0 9.9 0:00.03 ib_io_rd-2
...
后来装了一个8.0.28才发现确实是官方版本的新玩意。但是虽然能够猜到一些线程的功能，可还是很陌生的样子，因为这个名字和performance_schema.thread中的名字并不一样。
这里我们就来看看它的做法和对应关系。不过这一小步，却是DBA的一大步，我们以往在看Oracle的进程的时候都习惯了有命名的进程名字，这带来的好处是直接从OS层面就能判断大概哪个功能的压力增高。
二、以往的对应方法
我们知道以前在获取到线程的LWP号后需要到performance_schema.thread通过lwp和thread_os_id 对应，得到如下结果：
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
5524 mysql 20 0 4052588 792400 11676 S 0.0 27.4 0:03.82 mysqld
5533 mysql 20 0 4052588 792400 11676 S 0.0 27.4 0:00.00 mysqld
5556 mysql 20 0 4052588 792400 11676 S 0.0 27.4 0:00.00 mysqld
5557 mysql 20 0 4052588 792400 11676 S 0.0 27.4 0:00.00 mysqld
...
----------------------------------------+--------------+
| name | thread_os_id |
+----------------------------------------+--------------+
| thread/sql/main | 5524 |
| thread/sql/thread_timer_notifier | 5533 |
| thread/innodb/io_ibuf_thread | 5556 |
| thread/innodb/io_read_thread | 5558 |
| thread/innodb/io_log_thread | 5557 |
...
如果某个线程的CPU高或者IO高我们就能够知道是什么线程。当然你也可以和information_schema.processlist做join得到process id和state等有用的信息。
三、简单的实现方法讨论
比如以innodb为例，所有的线程的OS thread name都放到了all_innodb_threads这个一个数组中，其中每个元素是一个结构体，结构体中包含了我们OS thread name这个元素给予了大量的代码注释，我就放一点我们容易看懂的：
typedef struct PSI_thread_info_v5 PSI_thread_info;
The thread name to advertise to the operating system.
This feature is optional, and improves
observability for platforms that support
a flavor of pthread_setname_np().
这里我们也看到需要支持pthread_setname_np函数才行。在调用register_thread_class注册所有的class的时候会将这些OS thread name放到一个叫做thread_class_array全局内存中，这样再建立线程应该能轻松的从全局内存中拿到每个线程的OS thread name（当然我没去细看了）。接着，在建立线程的时候我们调用my_thread_self_setname设置OS thread name就可以了，实际上就是调用pthread_setname_np。
四、新的Linux OS thread name和performance_schema.threads中name的对应
为了快速的得到对应的办法，我稍微加了点输出内容，这样只要有线程启动，就会打印到error日志，因为如果一个一个去看每个线程启动的时候带入的OS thread name实在太慢了，耗不起，。得到的结果如下：
cat mysql3380.err |grep -w 'init threads'
[init threads] os name:boot -- mysql name:thread/sql/bootstrap
[init threads] os name:ib_io_ibuf -- mysql name:thread/innodb/io_ibuf_thread
[init threads] os name:ib_io_log -- mysql name:thread/innodb/io_log_thread
[init threads] os name:ib_io_rd-1 -- mysql name:thread/innodb/io_read_thread
[init threads] os name:ib_io_rd-2 -- mysql name:thread/innodb/io_read_thread
[init threads] os name:ib_io_rd-3 -- mysql name:thread/innodb/io_read_thread
[init threads] os name:ib_io_rd-4 -- mysql name:thread/innodb/io_read_thread
[init threads] os name:ib_io_rd-5 -- mysql name:thread/innodb/io_read_thread
[init threads] os name:ib_io_rd-6 -- mysql name:thread/innodb/io_read_thread
[init threads] os name:ib_io_rd-7 -- mysql name:thread/innodb/io_read_thread
[init threads] os name:ib_io_rd-8 -- mysql name:thread/innodb/io_read_thread
[init threads] os name:ib_io_wr-1 -- mysql name:thread/innodb/io_write_thread
[init threads] os name:ib_io_wr-2 -- mysql name:thread/innodb/io_write_thread
[init threads] os name:ib_io_wr-3 -- mysql name:thread/innodb/io_write_thread
[init threads] os name:ib_io_wr-4 -- mysql name:thread/innodb/io_write_thread
[init threads] os name:ib_pg_flush_co -- mysql name:thread/innodb/page_flush_coordinator_thread
[init threads] os name:ib_pg_flush-1 -- mysql name:thread/innodb/page_flush_thread
[init threads] os name:ib_pg_flush-2 -- mysql name:thread/innodb/page_flush_thread
[init threads] os name:ib_pg_flush-3 -- mysql name:thread/innodb/page_flush_thread
[init threads] os name:ib_recv_write -- mysql name:thread/innodb/recv_writer_thread
[init threads] os name:ib_log_checkpt -- mysql name:thread/innodb/log_checkpointer_thread
[init threads] os name:ib_log_fl_notif -- mysql name:thread/innodb/log_flush_notifier_thread
[init threads] os name:ib_log_flush -- mysql name:thread/innodb/log_flusher_thread
[init threads] os name:ib_log_wr_notif -- mysql name:thread/innodb/log_write_notifier_thread
[init threads] os name:ib_log_writer -- mysql name:thread/innodb/log_writer_thread
[init threads] os name:ib_par_rseg-0 -- mysql name:thread/innodb/parallel_rseg_init_thread
[init threads] os name:ib_par_rseg-0 -- mysql name:thread/innodb/parallel_rseg_init_thread
[init threads] os name:ib_srv_lock_to -- mysql name:thread/innodb/srv_lock_timeout_thread
[init threads] os name:ib_srv_err_mon -- mysql name:thread/innodb/srv_error_monitor_thread
[init threads] os name:ib_srv_mon -- mysql name:thread/innodb/srv_monitor_thread
[init threads] os name:ib_buf_resize -- mysql name:thread/innodb/buf_resize_thread
[init threads] os name:ib_src_main -- mysql name:thread/innodb/srv_master_thread
[init threads] os name:ib_dict_stats -- mysql name:thread/innodb/dict_stats_thread
[init threads] os name:ib_fts_opt -- mysql name:thread/innodb/fts_optimize_thread
[init threads] os name:xpl_worker-1 -- mysql name:thread/mysqlx/worker
[init threads] os name:xpl_worker-2 -- mysql name:thread/mysqlx/worker
[init threads] os name:xpl_accept-1 -- mysql name:thread/mysqlx/acceptor_network
[init threads] os name:ib_buf_dump -- mysql name:thread/innodb/buf_dump_thread
[init threads] os name:ib_clone_gtid -- mysql name:thread/innodb/clone_gtid_thread
[init threads] os name:ib_srv_purge -- mysql name:thread/innodb/srv_purge_thread
[init threads] os name:ib_srv_wkr-1 -- mysql name:thread/innodb/srv_worker_thread
[init threads] os name:ib_srv_wkr-2 -- mysql name:thread/innodb/srv_worker_thread
[init threads] os name:ib_srv_wkr-3 -- mysql name:thread/innodb/srv_worker_thread
[init threads] os name:sig_handler -- mysql name:thread/sql/signal_handler
[init threads] os name:xpl_accept-2 -- mysql name:thread/mysqlx/acceptor_network
[init threads] os name:xpl_accept-3 -- mysql name:thread/mysqlx/acceptor_network
[init threads] os name:gtid_zip -- mysql name:thread/sql/compress_gtid_table
[init threads] os name:connection -- mysql name:thread/sql/one_connection
可以看到建立的线程非常的多，但是我们得到它们的对应关系这就够了。这里不一一讨论每个线程的功能了，不过大部分我们都非常熟悉了，比如purge线程/cleaner线程 ，这里我列出一些，其他的就自己看看吧。
-
purge线程 srv_purge_thread 主要用于清理delete flag和释放undo表空间 -
clean线程 page_cleaner_thread DBWR 主要用于进行脏数据的刷盘和LRU链表的管理 -
异步IO线程 io_read_thread/io_write_thread 通常数据预读和刷脏会使用到异步AIO,用于合并可能的散列IO为连续IO提高性能 -
字典收集线程 dict_stats_thread 数据修改的10%后会触发统计数据的收集 -
锁超时监控线程srv_lock_timeout_thread 用于监控innodb行锁的超时，超时进行事务回退 -
GTID压缩线程compress_gtid_table 将历史的gtid压缩为范围，避免gtid_executed表过长 -
slave io线程 slave_io 从库接收来自DUMP线程的binlog Event。将这些Event写入到relay log。 -
slave dump线程 这是前台线程 主库监控binlog的变化，发送binlog Event -
slave sql线程 slave_sql 从库负责执行binlog Event -
用户线程one_connection 一个session就是一个用户线程，对于用户线程而言。可以通过processlist_id和show processlist -
srv_error_monitor_thread 所谓的信号量监控线程，注意这个信号量不是OS的信号量。是Innodb内部的rw lock和mutex -
srv_monitor_thread 这个线程当参数innodb_status_output打开的情况下，每15秒输出一个show engine innodb status信息到日志文件。也会自动开启比如Innodb内存不足会自动开启。 -
log_writer线程：将redo写到redo文件 -
log_write_notifier线程：通知用户会话写入redo文件结束 -
log_flusher线程：将redo fsync到redo文件 -
log_flush_notifier线程：通知用户会话fsync结束 -
log_checkpointer线程：定期检查脏数据写盘的redo 位置。
五、用pthread_setname_np为线程命名
这里我就随便写了4个循环的线程调用这个函数为我的线程命名为D-GPWK，需要耗用较高的CPU，看到的结果如下：
如果这个线程是MySQL的线程，当看到这个结果，我们就能明白大概的方向了（卧槽，慢SQL吧^_^）。
如果觉得本文有用，感谢各位朋友的转发