SQL優化之PostgreSQL的pg_stat_statements統計模塊

 pg_stat_statements模塊含義？

• pg_stat_statements模塊提供一種方法追蹤一個服務器所執行的所有 SQL 語句的執行統計信息，可以用於統計數據庫的資源開銷，分析TOP SQL。
• 如下所示表中所代表的字段：f放到

  • -- SQL統計
    SELECT 
    userid AS 執行者id ,
    dbid AS 執行數據庫id ,
    query AS 執行的語句 ,
    calls AS 執行次數 ,
    total_time AS 執行總時間,
    total_time/calls AS 執行平均時間,
    rows AS 影響的總行數,
    min_time,
    max_time,
    mean_time AS 平均時間
    FROM pg_stat_statements
    

     

•  最耗時的5條數據，最後一列表示命中率，由此我們可以拿出效率慢的sql進行優化。

  • SELECT query, calls, total_time, rows, 100.0 * shared_blks_hit /nullif(shared_blks_hit + shared_blks_read, 0) AS hit_percent FROM pg_stat_statements ORDER BY total_time DESC LIMIT 5;

• 各個字段代表的含義信息？

 

• 最耗時 SQL，單次調用最耗時 SQL TOP 5
  select userid::regrole, dbid, query from pg_stat_statements order by mean_time desc limit 5;  

• 最耗IO SQL，單次調用最耗IO SQL TOP 5
  select userid::regrole, dbid, query from pg_stat_statements order by (blk_read_time+blk_write_time)/calls desc limit 5;  

  

• 總最耗IO SQL TOP 5
  select userid::regrole, dbid, query from pg_stat_statements order by (blk_read_time+blk_write_time) desc limit 5;  

  

• 用戶也可以定期清理歷史的統計信息，通過調用如下SQL
  select pg_stat_statements_reset();  

• 響應時間抖動最嚴重 SQL
  select userid::regrole, dbid, query from pg_stat_statements order by stddev_time desc limit 5;  

• 最耗共享內存 SQL
  select userid::regrole, dbid, query from pg_stat_statements order by (shared_blks_hit+shared_blks_dirtied) desc limit 5;  

• 最耗臨時空間 SQL
  select userid::regrole, dbid, query from pg_stat_statements order by temp_blks_written desc limit 5;  
  
  

• 重置統計信息
  pg_stat_statements是累積的統計，如果要查看某個時間段的統計，需要打快照

 

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