Mysql調優之profile詳解

繁星落眼眶發表於2018-11-22

前言

  1. 在我們做mysql效能分析的時候,最常用的有三種方式:

    (1)慢查詢 (分析出現出問題的sql)
    (2)Explain (顯示了mysql如何使用索引來處理select語句以及連線表。可以幫助選擇更好的索引和寫出更優化的查詢語句)
    (3)Profile(查詢到 SQL 會執行多少時間, 並看出 CPU/Memory 使用量, 執行過程中 Systemlock, Table lock 花多少時間等等.)
  2. 本章主要是對profile做簡單的概述,用來對某一條sql語句進行效能分析。
  3. Profiling是從 mysql5.0.3版本以後才開放的。但是在mysql5.7之後,profile資訊將逐漸被廢棄,mysql推薦使用performance schema。
  4. profile此工具可用來查詢SQL執行狀態,System lock和Table lock 花多少時間等等,對定位一條語句的I/O消耗和CPU消耗 非常重要。(SQL 語句執行所消耗的最大兩部分資源就是IO和CPU)

profile工具使用

  1. 檢視自己的mysql版本:

    mysql> select version(); 
    +------------+
    | version()  |
    +------------+
    | 5.6.35-log |
    +------------+ 
  2. 檢視是否開啟profile功能(profiling=on代表開啟):

    mysql> show variables like `%profil%`;
    +------------------------+-------+
    | Variable_name          | Value |
    +------------------------+-------+
    | have_profiling        | YES  |
    | profiling              | OFF    |
    | profiling_history_size | 15    |
    +------------------------+-------+ 
  3. 開啟profile:

    mysql> set profile=1; 
  4. 開啟profile之後,執行要分析的sql語句:

    mysql> select t1.*,t2.action from pre_forum_thread as t1
    left join 
    (select a.* from pre_forum_threadmod as a,(select tid,max(dateline) as dateline from pre_forum_threadmod group by tid) as b
    where a.tid=b.tid and a.dateline=b.dateline) as t2
    on t1.tid=t2.tid
    where t1.displayorder>=0 and t1.fid in (47,49) and t1.tid > 100318 
    and (t1.authorid =7683017 or t2.action<>`DWN` or t2.action is null )
    order by t1.dateline desc limit 20;
  5. 檢視生成的profile資訊:

    mysql> show profiles;
    +----------+------------+--------------------------------------------------------------------------------------------------------+
    | Query_ID | Duration  | Query                                                                                                  |
    +----------+------------+--------------------------------------------------------------------------------------------------------+
    |        1 | 1.37183777 | select t1.*,t2.action from pre_forum_thread as t1  |
    |        2 | 0.00078796 | show columns from `bbs`.`t2` |
    |        3 | 0.00150425 | show columns from `bbs`.`pre_forum_thread` |
    +----------+------------+--------------------------------------------------------------------------------------------------------+
  6. 獲取指定的query語句的開銷:

    mysql> show profile for query 2; 
    +----------------------+----------+
    | Status              | Duration |
    +----------------------+----------+
    | starting            | 0.000147 |
    | checking permissions | 0.000023 |
    | Opening tables      | 0.000047 |
    | init                | 0.000081 |
    | System lock          | 0.000031 |
    | optimizing          | 0.000034 |
    | statistics          | 0.001650 |
    | preparing            | 0.000046 |
    | executing            | 0.000018 |
    | Sending data        | 2.460588 |
    | end                  | 0.000041 |
    | query end            | 0.000019 |
    | closing tables      | 0.000022 |
    | freeing items        | 0.000055 |
    | cleaning up          | 0.000085 |
    +----------------------+----------+ 
    
  7. 關閉profile:

    mysql> set profiling=0;
  8. 相關具體的引數:

    type: 
       ALL                --顯示所有的開銷資訊 
     | BLOCK IO          --顯示塊IO相關開銷 
     | CONTEXT SWITCHES  --上下文切換相關開銷 
     | CPU                --顯示CPU相關開銷資訊 
     | IPC                --顯示傳送和接收相關開銷資訊 
     | MEMORY            --顯示記憶體相關開銷資訊 
     | PAGE FAULTS        --顯示頁面錯誤相關開銷資訊 
     | SOURCE            --顯示和Source_function,Source_file,Source_line相關的開銷資訊 
     | SWAPS              --顯示交換次數相關開銷的資訊 
    
    例如,想要檢視cpu和io開銷可以執行命令:
    mysql> SHOW profile CPU,BLOCK IO  FOR query 2;

總結

  1. 一般簡易的流程:

    (1)set profiling=1; //開啟profile分析
    (2)run your sql1;
    (3)run your sql2;
    (4)show profiles;    //檢視sql1,sql2的語句分析
    (5)SHOW profile CPU,BLOCK IO io FOR query 1; //檢視CPU、IO消耗
    (6)set profiling=0; //關閉profile分析

參考連結

https://blog.csdn.net/ty_hf/a…
https://www.linuxidc.com/Linu…

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