能力有限，如果有誤請諒解。
一、問題來源
最近在檢查某個數(shù)據(jù)庫性能的時候，通過top -Hu mysql看到了一個特別奇怪的現(xiàn)象，線程有了自己的名字，我開始以為是哪個大廠自己維護的版本，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
...
后來裝了一個8.0.28才發(fā)現(xiàn)確實是官方版本的新玩意。但是雖然能夠猜到一些線程的功能，可還是很陌生的樣子，因為這個名字和performance_schema.thread中的名字并不一樣。
這里我們就來看看它的做法和對應(yīng)關(guān)系。不過這一小步，卻是DBA的一大步，我們以往在看Oracle的進程的時候都習(xí)慣了有命名的進程名字，這帶來的好處是直接從OS層面就能判斷大概哪個功能模塊的壓力增高。
二、以往的對應(yīng)方法
我們知道以前在獲取到線程的LWP號后需要到performance_schema.thread通過lwp和thread_os_id 對應(yīng)，得到如下結(jié)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 |
...
如果某個線程的CPU高或者IO高我們就能夠知道是什么線程。
三、簡單的實現(xiàn)方法討論
比如以innodb為例，所有的線程的OS thread name都放到了all_innodb_threads這個一個數(shù)組中，其中每個元素是一個結(jié)構(gòu)體，結(jié)構(gòu)體中包含了我們OS thread name這個元素給予了大量的代碼注釋，我就放一點我們?nèi)菀卓炊模?/p>
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().
這里我們也看到需要支持pthread_setname_np函數(shù)才行。
在調(diào)用register_thread_class注冊所有的class的時候會將這些OS thread name放到一個叫做thread_class_array全局內(nèi)存中，這樣再建立線程應(yīng)該能輕松的從全局內(nèi)存中拿到每個線程的OS thread name（當(dāng)然我沒去細看了）。
接著，在建立線程的時候我們調(diào)用my_thread_self_setname設(shè)置OS thread name就可以了，實際上就是調(diào)用pthread_setname_np。
四、新的Linux OS thread name和performance_schema.threads中name的對應(yīng)
為了快速的得到對應(yīng)的辦法，我稍微加了點輸出內(nèi)容，這樣只要有線程啟動，就會打印到error日志，因為如果一個一個去看每個線程啟動的時候帶入的OS thread name實在太慢了，耗不起，。
得到的結(jié)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
可以看到建立的線程非常的多，但是我們得到它們的對應(yīng)關(guān)系這就夠了。這里不一一討論每個線程的功能了，不過大部分我們都非常熟悉了，比如purge線程/cleaner線程 ，這里我列出一些，其他的就自己看看吧。
- purge線程 srv_purge_thread
主要用于清理delete flag和釋放undo表空間 - clean線程 page_cleaner_thread DBWR
主要用于進行臟數(shù)據(jù)的刷盤和LRU鏈表的管理 - 異步IO線程 io_read_thread/io_write_thread
通常數(shù)據(jù)預(yù)讀和刷臟會使用到異步AIO,用于合并可能的散列IO為連續(xù)IO提高性能 - 字典收集線程 dict_stats_thread
數(shù)據(jù)修改的10%后會觸發(fā)統(tǒng)計數(shù)據(jù)的收集 - 鎖超時家監(jiān)控線程srv_lock_timeout_thread
用于監(jiān)控innodb行鎖的超時，超時進行事務(wù)回退 - GTID壓縮線程compress_gtid_table
將歷史的gtid壓縮為范圍，避免gtid_executed表過長 - slave io線程 slave_io
從庫接收來自DUMP線程的binlog Event。將這些Event寫入到relay log。 - slave dump線程 這是前臺線程
主庫監(jiān)控binlog的變化，發(fā)送binlog Event - slave sql線程 slave_sql
從庫負(fù)責(zé)執(zhí)行binlog Event - 用戶線程one_connection
一個session就是一個用戶線程，對于用戶線程而言?？梢酝ㄟ^processlist_id和show processlist - srv_error_monitor_thread
所謂的信號量監(jiān)控線程，注意這個信號量不是OS的信號量。是Innodb內(nèi)部的rw lock和mutex - srv_monitor_thread
這個線程當(dāng)參數(shù)innodb_status_output打開的情況下，每15秒輸出一個show engine innodb status信息到日志文件。也會自動開啟比如Innodb內(nèi)存不足會自動開啟。 - log_writer線程：將redo寫到redo文件
- log_write_notifier線程：通知用戶會話寫入redo文件結(jié)束
- log_flusher線程：將redo fsync到redo文件
- log_flush_notifier線程：通知用戶會話fsync結(jié)束
- log_checkpointer線程：定期檢查臟數(shù)據(jù)寫盤的redo 位置。
五、用pthread_setname_np為線程命名
這里我就隨便寫了4個循環(huán)的線程調(diào)用這個函數(shù)為我的線程命名為D-GPWK，需要耗用較高的CPU，看到的結(jié)果如下：
image.png
如果這個線程是MySQL的線程，當(dāng)看到這個結(jié)果，我們就能明白大概的方向了（臥槽，慢SQL吧^_^）。
如果覺得本文有用，感謝各位的轉(zhuǎn)發(fā)
