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。
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：
image.png
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
原创文章，作者：筱凯，如若转载，请注明出处：https://www.jingyueyun.com/ask/473.html
