MySQL optimizer_trace的用法

  > 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                                                                         |
  +------------------------------+----------------------------------------------------------------------------+

  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');

  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;

> SELECT * FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE \G

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

> SET OPTIMIZER_TRACE="enabled=off";