MySQL optimizer_trace的用法

Posted 2021-12-11 我的二狗呢

​​ https://dev.mysql.com/doc/internals/en/system-variables-controlling-trace.html ​​

​​ https://dev.mysql.com/doc/internals/en/tracing-example.html ​​

  > show global variables like optim%trace%  -- 默认配置
  +------------------------------+----------------------------------------------------------------------------+
  | Variable_name                | Value                                                                      |
  +------------------------------+----------------------------------------------------------------------------+
  | optimizer_trace              | enabled=off,one_line=off                                                   |
  | optimizer_trace_features     | greedy_search=on,range_optimizer=on,dynamic_range=on,repeated_subselect=on |
  | optimizer_trace_limit        | 1                                                                          |
  | optimizer_trace_max_mem_size | 1048576                                                                    |
  | optimizer_trace_offset       | -1                                                                         |
  +------------------------------+----------------------------------------------------------------------------+
  
  > SET OPTIMIZER_TRACE="enabled=on";
  > SET END_MARKERS_IN_JSON=on;
  > set optimizer_trace_max_mem_size=1000000;
  > SET optimizer_trace_offset=-5, optimizer_trace_limit=5;  -- 显示最后五个trace
  > show variables like %optimize%trace%;
  +------------------------------+----------------------------------------------------------------------------+
  | Variable_name                | Value                                                                      |
  +------------------------------+----------------------------------------------------------------------------+
  | optimizer_trace              | enabled=on,one_line=off                                                    |
  | optimizer_trace_features     | greedy_search=on,range_optimizer=on,dynamic_range=on,repeated_subselect=on |
  | optimizer_trace_limit        | 5                                                                          |
  | optimizer_trace_max_mem_size | 1000000                                                                    |
  | optimizer_trace_offset       | -5                                                                         |
  +------------------------------+----------------------------------------------------------------------------+

然后再模拟些业务数据（这段来自官方文档https://dev.mysql.com/doc/internals/en/tracing-example.html）

  CREATE TABLE t1 (
  pk INT,
  col_int_key INT,
  col_varchar_key VARCHAR (1),
  col_varchar_nokey VARCHAR (1)
  );

  INSERT INTO t1 VALUES
  (10,7,v,v),(11,0,s,s),(12,9,l,l),(13,3,y,y),(14,4,c,c),
  (15,2,i,i),(16,5,h,h),(17,3,q,q),(18,1,a,a),(19,3,v,v),
  (20,6,u,u),(21,7,s,s),(22,5,y,y),(23,1,z,z),(24,204,h,h),
  (25,224,p,p),(26,9,e,e),(27,5,i,i),(28,0,y,y),(29,3,w,w);
  
  CREATE TABLE t2 (
  pk INT, col_int_key INT,
  col_varchar_key VARCHAR(1), col_varchar_nokey VARCHAR(1),
  PRIMARY KEY (pk)
  );

  INSERT INTO t2 VALUES
  (1,4,b,b),(2,8,y,y),(3,0,p,p),(4,0,f,f),(5,0,p,p),
  (6,7,d,d),(7,7,f,f),(8,5,j,j),(9,3,e,e),(10,188,u,u),
  (11,4,v,v),(12,9,u,u),(13,6,i,i),(14,1,x,x),(15,5,l,l),
  (16,6,q,q),(17,2,n,n),(18,4,r,r),(19,231,c,c),(20,4,h,h),
  (21,3,k,k),(22,3,t,t),(23,7,t,t),(24,6,k,k),(25,7,g,g),
  (26,9,z,z),(27,4,n,n),(28,4,j,j),(29,2,l,l),(30,1,d,d),
  (31,2,t,t),(32,194,y,y),(33,2,i,i),(34,3,j,j),(35,8,r,r),
  (36,4,b,b),(37,9,o,o),(38,4,k,k),(39,5,a,a),(40,5,f,f),
  (41,9,t,t),(42,3,c,c),(43,8,c,c),(44,0,r,r),(45,98,k,k),
  (46,3,l,l),(47,1,o,o),(48,0,t,t),(49,189,v,v),(50,8,x,x),
  (51,3,j,j),(52,3,x,x),(53,9,k,k),(54,6,o,o),(55,8,z,z),
  (56,3,n,n),(57,9,c,c),(58,5,d,d),(59,9,s,s),(60,2,j,j),
  (61,2,w,w),(62,5,f,f),(63,8,p,p),(64,6,o,o),(65,9,f,f),
  (66,0,x,x),(67,3,q,q),(68,6,g,g),(69,5,x,x),(70,8,p,p),
  (71,2,q,q),(72,120,q,q),(73,25,v,v),(74,1,g,g),(75,3,l,l),
  (76,1,w,w),(77,3,h,h),(78,153,c,c),(79,5,o,o),(80,9,o,o),
  (81,1,v,v),(82,8,y,y),(83,7,d,d),(84,6,p,p),(85,2,z,z),
  (86,4,t,t),(87,7,b,b),(88,3,y,y),(89,8,k,k),(90,4,c,c),
  (91,6,z,z),(92,1,t,t),(93,7,o,o),(94,1,u,u),(95,0,t,t),
  (96,2,k,k),(97,7,u,u),(98,2,b,b),(99,1,m,m),(100,5,o,o);

模拟个业务查询

  SELECT
  SUM(alias2.col_varchar_nokey),
  alias2.pk AS field2
  FROM
  t1 AS alias1
  STRAIGHT_JOIN t2 AS alias2
    ON alias2.pk = alias1.col_int_key
  WHERE alias1.pk
  GROUP BY field2
  ORDER BY alias1.col_int_key,
  alias2.pk;

看下捕获到的sql的trace情况

> SELECT * FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE \\G

注意：

 每个记住的trace都是一个字符串。它随着优化的进行而扩展（使用 realloc()）并向其追加数据。  

 optimizer_trace_max_mem_size 变量对所有当前记住的trace使用的内存总量设置限制：如果达到此限制，则不会扩展当前跟踪（因此trace的结果显式将不完整）。

还可以把结果导出到文件（使用 INTO DUMPFILE 而不是 INTO OUTFILE ，因为后者会转义换行符。需要关闭end_markers_in_json，不然导出结果可能会不符合标准json）

> SELECT TRACE INTO DUMPFILE /tmp/aaa FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE;

用完记得关闭（当然不关闭也没问题，我们这里用的是session级别的设置）

> SET OPTIMIZER_TRACE="enabled=off";