MySQL:Innodb Handler_read_*变量解释

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发布于 2019-10-31 17:37:09

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发布于 2019-10-31 17:37:09

文章被收录于专栏：idbaidba

导读：

作者：高鹏（网名八怪），《深入理解MySQL主从原理32讲》系列文的作者本文为源码版本Percona 5.7.14，水平有限如果有误，请谅解

一、Handler_read_*值的实质

内部表示如下：

{"Handler_read_first",       (char*) offsetof(STATUS_VAR, ha_read_first_count),     SHOW_LONGLONG_STATUS,    SHOW_SCOPE_ALL},
{"Handler_read_key",         (char*) offsetof(STATUS_VAR, ha_read_key_count),       SHOW_LONGLONG_STATUS,    SHOW_SCOPE_ALL},
{"Handler_read_last",        (char*) offsetof(STATUS_VAR, ha_read_last_count),      SHOW_LONGLONG_STATUS,    SHOW_SCOPE_ALL},
{"Handler_read_next",        (char*) offsetof(STATUS_VAR, ha_read_next_count),      SHOW_LONGLONG_STATUS,    SHOW_SCOPE_ALL},
{"Handler_read_prev",        (char*) offsetof(STATUS_VAR, ha_read_prev_count),      SHOW_LONGLONG_STATUS,    SHOW_SCOPE_ALL},
{"Handler_read_rnd",         (char*) offsetof(STATUS_VAR, ha_read_rnd_count),       SHOW_LONGLONG_STATUS,    SHOW_SCOPE_ALL},
{"Handler_read_rnd_next",    (char*) offsetof(STATUS_VAR, ha_read_rnd_next_count),  SHOW_LONGLONG_STATUS,    SHOW_SCOPE_ALL},

实际上这些变量都是MySQL层定义出来的，因为MySQL可以包含多个存储引擎。因此这些值如何增加需要在引擎层的接口中自行实现，也就是说各个引擎都有自己的实现，在MySQL层进行汇总，因此这些值不是某个引擎特有的，打个比方如果有Innodb和MyISAM引擎，那么这些值是两个引擎的总和。本文将以Innodb为主要学习对象进行解释。

二、各个值的解释

1、Handler_read_key

内部表示：ha_read_key_count
Innodb更改接口：ha_innobase::index_read
文档解释：The number of requests to read a row based on a key. If this value is high, it is a good indication that your tables are properly indexed for your queries.
源码函数解释：Positions an index cursor to the index specified in the handle. Fetches the row if any.
作者解释：这个函数是访问索引的时候定位到值所在的位置用到的函数，因为必须要知道读取索引的开始位置才能向下访问。

2、Handler_read_next

内部表示：ha_read_next_count
Innodb更改接口：ha_innobase::index_next_same ha_innobase::index_next
文档解释：The number of requests to read the next row in key order. This value is incremented if you are querying an index column with a range constraint or if you are doing an index scan.
源码函数解释： index_next - Reads the next row from a cursor, which must have previously been positioned using index_read. index_next_same - Reads the next row matching to the key value given as the parameter.
作者解释：访问索引的下一条数据封装的ha_innobase::general_fetch函数，index_next_same和index_next不同在于访问的方式不一样，比如范围range查询需要用到和索引全扫描也会用到index_next，而ref访问方式会使用index_next_same

3、Handler_read_first

内部表示：ha_read_first_count
Innodb更改接口：ha_innobase::index_first
文档解释：The number of times the first entry in an index was read. If this value is high, it suggests that the server is doing a lot of full index scans; for example, SELECT col1 FROM foo, assuming that col1 is indexed
源码函数解释：Positions a cursor on the first record in an index and reads the corresponding row to buf.
作者解释：定位索引的第一条数据，实际上也是封装的ha_innobase::index_read 函数(如全表扫描/全索引扫描调用)

4、Handler_read_rnd_next

内部表示：ha_read_rnd_next_count
Innodb更改接口：ha_innobase::rnd_next
文档解释：The number of requests to read the next row in the data file. This value is high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have.
源码函数解释：Reads the next row in a table scan (also used to read the FIRST row in a table scan).
作者解释：全表扫描访问下一条数据，实际上也是封装的ha_innobase::general_fetch，在访问之前会调用ha_innobase::index_first

5、Handler_read_rnd

内部表示：ha_read_rnd_count
Innodb更改接口：ha_innobase::rnd_pos
Memory更改接口：ha_heap::rnd_pos
文档解释：The number of requests to read a row based on a fixed position. This value is high if you are doing a lot of queries that require sorting of the result. You probably have a lot of queries that require MySQL to scan entire tables or you have joins that do not use keys properly.
作者解释：这个状态值在我测试期间只发现对临时表做排序的时候会用到，而且是Memory引擎的，具体只能按照文档理解了。

6、其他

最后2个简单说一下

Handler_read_prev Innodb接口为 ha_innobase::index_prev 访问索引的上一条数据，实际上也是封装的ha_innobase::general_fetch函数，用于ORDER BY DESC 索引扫描避免排序，内部状态值ha_read_prev_count增加。
Handler_read_last Innodb接口为ha_innobase::index_last 访问索引的最后一条数据作为定位，实际上也是封装的ha_innobase::index_read函数，用于ORDER BY DESC 索引扫描避免排序，内部状态值ha_read_last_count增加。

三、常用查询测试

1、测试用例

mysql> show create table z1;
+-------+-------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                              |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------+
| z1    | CREATE TABLE `z1` (
  `a` int(11) DEFAULT NULL,
  `name` varchar(20) DEFAULT NULL,
  KEY `a` (`a`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show create table z10;
+-------+------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                   |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------+
| z10   | CREATE TABLE `z10` (
  `a` int(11) DEFAULT NULL,
  `name` varchar(20) DEFAULT NULL,
  KEY `a_idx` (`a`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> select count(*) from z1;
+----------+
| count(*) |
+----------+
|    56415 |
+----------+
1 row in set (5.27 sec)

mysql> select count(*) from z10;
+----------+
| count(*) |
+----------+
|       10 |
+----------+
1 row in set (0.00 sec)

2、全表扫描

mysql> desc select * from z1;
+----+-------------+-------+------------+------+---------------+------+---------+------+-------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows  | filtered | Extra |
+----+-------------+-------+------------+------+---------------+------+---------+------+-------+----------+-------+
|  1 | SIMPLE      | z1    | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 56650 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+------+---------+------+-------+----------+-------+
1 row in set, 1 warning (0.00 sec)

mysql> pager cat >>/dev/null
PAGER set to 'cat >>/dev/null'
mysql> flush status;
Query OK, 0 rows affected (0.10 sec)
mysql> select * from z1;
56415 rows in set (4.05 sec)
mysql> pager;
Default pager wasn't set, using stdout.
mysql> show status like 'Handler_read%';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| Handler_read_first    | 1     |
| Handler_read_key      | 1     |
| Handler_read_last     | 0     |
| Handler_read_next     | 0     |
| Handler_read_prev     | 0     |
| Handler_read_rnd      | 0     |
| Handler_read_rnd_next | 56416 |
+-----------------------+-------+
7 rows in set (0.01 sec)

Handler_read_first增加1次用于初次定位，Handler_read_key增加1次，Handler_read_rnd_next增加扫描行数。我们前面说过因为ha_innobase::index_first也是封装的ha_innobase::index_read因此都需要+1。

3、全索引扫描

mysql> desc select a from z1;
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-------------+
| id | select_type | table | partitions | type  | possible_keys | key  | key_len | ref  | rows  | filtered | Extra       |
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-------------+
|  1 | SIMPLE      | z1    | NULL       | index | NULL          | a    | 5       | NULL | 56650 |   100.00 | Using index |
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

mysql> flush status;
Query OK, 0 rows affected (0.12 sec)

mysql> pager cat >>/dev/null
PAGER set to 'cat >>/dev/null'
mysql> select a from z1;
56415 rows in set (4.57 sec)

mysql> pager
Default pager wasn't set, using stdout.
mysql> show status like 'Handler_read%';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| Handler_read_first    | 1     |
| Handler_read_key      | 1     |
| Handler_read_last     | 0     |
| Handler_read_next     | 56415 |
| Handler_read_prev     | 0     |
| Handler_read_rnd      | 0     |
| Handler_read_rnd_next | 0     |
+-----------------------+-------+
7 rows in set (0.01 sec)

Handler_read_first增加1次用于初次定位，Handler_read_key增加1次，Handler_read_next增加扫描行数用于连续访问接下来的行。我们前面说过因为ha_innobase::index_first也是封装的ha_innobase::index_read因此都需要+1。

4、索引ref访问

我这里因为是测试索引全是等于10的加上了force index

mysql>  desc select  * from z1 force index(a) where a=10;
+----+-------------+-------+------------+------+---------------+------+---------+-------+-------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref   | rows  | filtered | Extra |
+----+-------------+-------+------------+------+---------------+------+---------+-------+-------+----------+-------+
|  1 | SIMPLE      | z1    | NULL       | ref  | a             | a    | 5       | const | 28325 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+------+---------+-------+-------+----------+-------+
1 row in set, 1 warning (0.01 sec)

mysql> flush status;
Query OK, 0 rows affected (0.13 sec)

mysql> pager cat >>/dev/null
PAGER set to 'cat >>/dev/null'
mysql> select  * from z1 force index(a) where a=10;
56414 rows in set (32.39 sec)
mysql> pager
Default pager wasn't set, using stdout.
mysql> show status like 'Handler_read%';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| Handler_read_first    | 0     |
| Handler_read_key      | 1     |
| Handler_read_last     | 0     |
| Handler_read_next     | 56414 |
| Handler_read_prev     | 0     |
| Handler_read_rnd      | 0     |
| Handler_read_rnd_next | 0     |
+-----------------------+-------+
7 rows in set (0.06 sec)

Handler_read_key增加1次这是用于初次定位，Handler_read_next增加扫描行数次数用于接下来的数据访问。

5、索引range访问

mysql> desc select  * from z1 force index(a) where a>9 and a<12;
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-----------------------+
| id | select_type | table | partitions | type  | possible_keys | key  | key_len | ref  | rows  | filtered | Extra                 |
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-----------------------+
|  1 | SIMPLE      | z1    | NULL       | range | a             | a    | 5       | NULL | 28325 |   100.00 | Using index condition |
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-----------------------+
1 row in set, 1 warning (0.00 sec)

mysql>  pager cat >>/dev/null
PAGER set to 'cat >>/dev/null'
mysql> select  * from z1 force index(a) where a>9 and a<12;
56414 rows in set (47.54 sec)
mysql> show status like 'Handler_read%';
7 rows in set (0.03 sec)
mysql>  pager
Default pager wasn't set, using stdout.
mysql> show status like 'Handler_read%';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| Handler_read_first    | 0     |
| Handler_read_key      | 1     |
| Handler_read_last     | 0     |
| Handler_read_next     | 56414 |
| Handler_read_prev     | 0     |
| Handler_read_rnd      | 0     |
| Handler_read_rnd_next | 0     |
+-----------------------+-------+
7 rows in set (0.02 sec)

Handler_read_key增加1次这是用于初次定位，Handler_read_next增加扫描行数次数用于接下来的数据访问。

6、被驱动表带索引访问

mysql> desc select * from z1 STRAIGHT_JOIN z10 force index(a_idx) on z1.a=z10.a;
+----+-------------+-------+------------+------+---------------+-------+---------+-----------+-------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key   | key_len | ref       | rows  | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+-------+---------+-----------+-------+----------+-------------+
|  1 | SIMPLE      | z1    | NULL       | ALL  | a             | NULL  | NULL    | NULL      | 56650 |   100.00 | Using where |
|  1 | SIMPLE      | z10   | NULL       | ref  | a_idx         | a_idx | 5       | test.z1.a |    10 |   100.00 | NULL        |
+----+-------------+-------+------------+------+---------------+-------+---------+-----------+-------+----------+-------------+
2 rows in set, 1 warning (0.01 sec)

mysql> flush status;
Query OK, 0 rows affected (0.47 sec)

mysql> pager cat >> /dev/null
PAGER set to 'cat >> /dev/null'
mysql>  select * from z1 STRAIGHT_JOIN z10 force index(a_idx) on z1.a=z10.a;
112828 rows in set (1 min 21.21 sec)

mysql> pager
Default pager wasn't set, using stdout.
mysql>  show status like 'Handler_read%';
+-----------------------+--------+
| Variable_name         | Value  |
+-----------------------+--------+
| Handler_read_first    | 1      |
| Handler_read_key      | 56416  |
| Handler_read_last     | 0      |
| Handler_read_next     | 112828 |
| Handler_read_prev     | 0      |
| Handler_read_rnd      | 0      |
| Handler_read_rnd_next | 56416  |
+-----------------------+--------+
7 rows in set (0.00 sec)

Handler_read_first 增加一次作为驱动表z1全表扫描定位的开始，接下来Handler_read_rnd_next扫描全部记录，每次扫描一次在z10表通过索引a_idx定位一次Handler_read_key增加1次，然后接下来进行索引a_idx进行数据查找Handler_read_next增加为扫描的行数。

7、索引避免排序正向和反向

mysql>  flush status;
Query OK, 0 rows affected (0.05 sec)

mysql> pager cat >> /dev/null
PAGER set to 'cat >> /dev/null'
mysql> select * from z1 force index(a) order by a;
56415 rows in set (27.39 sec)

mysql> pager
Default pager wasn't set, using stdout.
mysql> show status like 'Handler_read%';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| Handler_read_first    | 1     |
| Handler_read_key      | 1     |
| Handler_read_last     | 0     |
| Handler_read_next     | 56415 |
| Handler_read_prev     | 0     |
| Handler_read_rnd      | 0     |
| Handler_read_rnd_next | 0     |
+-----------------------+-------+
7 rows in set (0.01 sec)

mysql> flush status;
Query OK, 0 rows affected (0.10 sec)

mysql> desc  select * from z1 force index(a) order by a desc;
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-------+
| id | select_type | table | partitions | type  | possible_keys | key  | key_len | ref  | rows  | filtered | Extra |
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-------+
|  1 | SIMPLE      | z1    | NULL       | index | NULL          | a    | 5       | NULL | 56650 |   100.00 | NULL  |
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-------+
1 row in set, 1 warning (0.00 sec)

mysql> pager cat >> /dev/null
PAGER set to 'cat >> /dev/null'
mysql>  select * from z1 force index(a) order by a desc;
56415 rows in set (24.94 sec)

mysql> pager
Default pager wasn't set, using stdout.
mysql>  show status like 'Handler_read%';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| Handler_read_first    | 0     |
| Handler_read_key      | 1     |
| Handler_read_last     | 1     |
| Handler_read_next     | 0     |
| Handler_read_prev     | 56415 |
| Handler_read_rnd      | 0     |
| Handler_read_rnd_next | 0     |
+-----------------------+-------+
7 rows in set (0.01 sec)

不用过多解释，可以看到Handler_read_last 和Handler_read_prev的用途。

四、总结

Handler_read_rnd_next 通常代表着全表扫描。
Handler_read_first 通常代表着全表或者全索引扫描。
Handler_read_next 通常代表着合理的使用了索引或者全索引扫描。
Handler_read_key 不管全表全索引或者正确使用的索引实际上都会增加，只是一次索引定位而已。
Innodb中全表扫描也是主键的全索引扫描。
顺序访问的一条记录实际上都是调用ha_innobase::general_fetch函数，另外一个功能innodb_thread_concurrency参数的功能就在里面实现，下次在说。

五、参考栈帧

全表扫描
mysql> desc  select * from z1 ;+----+-------------+-------+------------+------+---------------+------+---------+------+-------+----------+-------+| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows  | filtered | Extra |+----+-------------+-------+------------+------+---------------+------+---------+------+-------+----------+-------+|  1 | SIMPLE      | z1    | NULL       | ALL  | NULL          | NULL | NULL    | NULL | 56650 |   100.00 | NULL  |+----+-------------+-------+------------+------+---------------+------+---------+------+-------+----------+-------+1 row in set, 1 warning (0.00 sec)
第一次:#0  row_search_mvcc (buf=0x7fff2ccc9380 "\377", mode=PAGE_CUR_G, prebuilt=0x7fff2cd4bb40, match_mode=0, direction=0)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/row/row0sel.cc:4479#1  0x00000000019b3051 in ha_innobase::index_read (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\377", key_ptr=0x0, key_len=0, find_flag=HA_READ_AFTER_KEY)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9104#2  0x00000000019b4374 in ha_innobase::index_first (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\377")    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9551#3  0x00000000019b462c in ha_innobase::rnd_next (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\377")    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9656#4  0x0000000000f66fa2 in handler::ha_rnd_next (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\377") at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:3099#5  0x00000000014c61b6 in rr_sequential (info=0x7fff2c0026a0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/records.cc:520#6  0x000000000155f2a4 in join_init_read_record (tab=0x7fff2c002650) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:2481#7  0x000000000155c381 in sub_select (join=0x7fff2c001f70, qep_tab=0x7fff2c002650, end_of_records=false)    at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:1271#8  0x000000000155bd06 in do_select (join=0x7fff2c001f70) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:944#9  0x0000000001559bdc in JOIN::exec (this=0x7fff2c001f70) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:199

随后访问:#0  row_search_mvcc (buf=0x7fff2ccc9380 "\376\n", mode=PAGE_CUR_UNSUPP, prebuilt=0x7fff2cd4bb40, match_mode=0, direction=1)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/row/row0sel.cc:4479#1  0x00000000019b3f50 in ha_innobase::general_fetch (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n", direction=1, match_mode=0)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9425#2  0x00000000019b4666 in ha_innobase::rnd_next (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n")    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9664#3  0x0000000000f67026 in handler::ha_rnd_next (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n") at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:3099#4  0x00000000014c61b6 in rr_sequential (info=0x7fff2c0026a0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/records.cc:520#5  0x000000000155c397 in sub_select (join=0x7fff2c001f70, qep_tab=0x7fff2c002650, end_of_records=false)    at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:1274#6  0x000000000155bd06 in do_select (join=0x7fff2c001f70) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:944#7  0x0000000001559bdc in JOIN::exec (this=0x7fff2c001f70) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:199


全索引扫描


mysql> desc select a from z1 ;+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-------------+| id | select_type | table | partitions | type  | possible_keys | key  | key_len | ref  | rows  | filtered | Extra       |+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-------------+|  1 | SIMPLE      | z1    | NULL       | index | NULL          | a    | 5       | NULL | 56650 |   100.00 | Using index |+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-------------+1 row in set, 1 warning (0.00 sec)

第一次:#0  row_search_mvcc (buf=0x7fff2ccc9380 "\377", mode=PAGE_CUR_G, prebuilt=0x7fff2cd4bb40, match_mode=0, direction=0)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/row/row0sel.cc:4479#1  0x00000000019b3051 in ha_innobase::index_read (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\377", key_ptr=0x0, key_len=0, find_flag=HA_READ_AFTER_KEY)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9104#2  0x00000000019b4374 in ha_innobase::index_first (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\377")    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9551#3  0x0000000000f686f4 in handler::ha_index_first (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\377") at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:3337#4  0x000000000155f997 in join_read_first (tab=0x7fff2c002578) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:2646#5  0x000000000155c381 in sub_select (join=0x7fff2c001e98, qep_tab=0x7fff2c002578, end_of_records=false)    at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:1271#6  0x000000000155bd06 in do_select (join=0x7fff2c001e98) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:944#7  0x0000000001559bdc in JOIN::exec (this=0x7fff2c001e98) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:199
随后访问:#0  row_search_mvcc (buf=0x7fff2ccc9380 "\376\n", mode=PAGE_CUR_UNSUPP, prebuilt=0x7fff2cd4bb40, match_mode=0, direction=1)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/row/row0sel.cc:4479#1  0x00000000019b3f50 in ha_innobase::general_fetch (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n", direction=1, match_mode=0)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9425#2  0x00000000019b4261 in ha_innobase::index_next (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n")    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9503#3  0x0000000000f680d8 in handler::ha_index_next (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n") at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:3269#4  0x000000000155fa02 in join_read_next (info=0x7fff2c0025c8) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:2660#5  0x000000000155c397 in sub_select (join=0x7fff2c001e98, qep_tab=0x7fff2c002578, end_of_records=false)    at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:1274#6  0x000000000155bd06 in do_select (join=0x7fff2c001e98) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:944#7  0x0000000001559bdc in JOIN::exec (this=0x7fff2c001e98) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:199


索引ref const
mysql> desc  select * from z1 where a=10;+----+-------------+-------+------------+------+---------------+------+---------+-------+-------+----------+-------+| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref   | rows  | filtered | Extra |+----+-------------+-------+------------+------+---------------+------+---------+-------+-------+----------+-------+|  1 | SIMPLE      | z1    | NULL       | ref  | a             | a    | 5       | const | 28325 |   100.00 | NULL  |+----+-------------+-------+------------+------+---------------+------+---------+-------+-------+----------+-------+1 row in set, 1 warning (0.00 sec)

初次访问：#0  row_search_mvcc (buf=0x7fff2ccc9380 "\376\n", mode=PAGE_CUR_GE, prebuilt=0x7fff2cd4bb40, match_mode=1, direction=0)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/row/row0sel.cc:4479#1  0x00000000019b3051 in ha_innobase::index_read (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n", key_ptr=0x7fff2cddf0d0 "", key_len=5, find_flag=HA_READ_KEY_EXACT)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9104#2  0x0000000000f75dc4 in handler::index_read_map (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n", key=0x7fff2cddf0d0 "", keypart_map=1, find_flag=HA_READ_KEY_EXACT)    at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.h:2843#3  0x0000000000f675fa in handler::ha_index_read_map (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n", key=0x7fff2cddf0d0 "", keypart_map=1,    find_flag=HA_READ_KEY_EXACT) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:3183#4  0x000000000155e9ab in join_read_always_key (tab=0x7fff2cddf1d0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:2260#5  0x000000000155c381 in sub_select (join=0x7fff2c002528, qep_tab=0x7fff2cddf1d0, end_of_records=false)    at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:1271#6  0x000000000155bd06 in do_select (join=0x7fff2c002528) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:944#7  0x0000000001559bdc in JOIN::exec (this=0x7fff2c002528) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:199

随后访问#0  row_search_mvcc (buf=0x7fff2ccc9380 "\376\n", mode=PAGE_CUR_UNSUPP, prebuilt=0x7fff2cd4bb40, match_mode=1, direction=1)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/row/row0sel.cc:4479#1  0x00000000019b3f50 in ha_innobase::general_fetch (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n", direction=1, match_mode=1)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9425#2  0x00000000019b42b5 in ha_innobase::index_next_same (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n", key=0x7fff2cddf0d0 "", keylen=5)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9519#3  0x0000000000f68e37 in handler::ha_index_next_same (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n", key=0x7fff2cddf0d0 "", keylen=5)    at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:3407#4  0x000000000155ebd4 in join_read_next_same (info=0x7fff2cddf220) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:2319#5  0x000000000155c397 in sub_select (join=0x7fff2c002528, qep_tab=0x7fff2cddf1d0, end_of_records=false)    at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:1274#6  0x000000000155bd06 in do_select (join=0x7fff2c002528) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:944#7  0x0000000001559bdc in JOIN::exec (this=0x7fff2c002528) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:199



索引 range
mysql> desc select * from z1 force index(a) where a>=10 and a<12;+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-----------------------+| id | select_type | table | partitions | type  | possible_keys | key  | key_len | ref  | rows  | filtered | Extra                 |+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-----------------------+|  1 | SIMPLE      | z1    | NULL       | range | a             | a    | 5       | NULL | 28325 |   100.00 | Using index condition |+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+-----------------------+1 row in set, 1 warning (0.03 sec)
初次访问：0  row_search_mvcc (buf=0x7fff2ccc9380 "\377", mode=PAGE_CUR_GE, prebuilt=0x7fff2cd4bb40, match_mode=0, direction=0)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/row/row0sel.cc:4479#1  0x00000000019b3051 in ha_innobase::index_read (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\377", key_ptr=0x7fff2ce21bc0 "", key_len=5, find_flag=HA_READ_KEY_OR_NEXT)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9104#2  0x0000000000f75dc4 in handler::index_read_map (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\377", key=0x7fff2ce21bc0 "", keypart_map=1, find_flag=HA_READ_KEY_OR_NEXT)    at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.h:2843#3  0x0000000000f675fa in handler::ha_index_read_map (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\377", key=0x7fff2ce21bc0 "", keypart_map=1,    find_flag=HA_READ_KEY_OR_NEXT) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:3183#4  0x0000000000f7186e in handler::read_range_first (this=0x7fff2cd32480, start_key=0x7fff2cd32568, end_key=0x7fff2cd32588, eq_range_arg=false, sorted=false)    at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:7565#5  0x0000000000f6f7cd in handler::multi_range_read_next (this=0x7fff2cd32480, range_info=0x7ffff03598c0)    at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:6635#6  0x0000000000f706b7 in DsMrr_impl::dsmrr_next (this=0x7fff2cd328f0, range_info=0x7ffff03598c0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:7019#7  0x00000000019c6210 in ha_innobase::multi_range_read_next (this=0x7fff2cd32480, range_info=0x7ffff03598c0)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:21372#8  0x00000000017904b2 in QUICK_RANGE_SELECT::get_next (this=0x7fff2ccc9760) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/opt_range.cc:11171#9  0x00000000014c5f56 in rr_quick (info=0x7fff2cddf050) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/records.cc:398#10 0x000000000155f2a4 in join_init_read_record (tab=0x7fff2cddf000) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:2481#11 0x000000000155c381 in sub_select (join=0x7fff2cdde4e0, qep_tab=0x7fff2cddf000, end_of_records=false)    at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:1271#12 0x000000000155bd06 in do_select (join=0x7fff2cdde4e0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:944#13 0x0000000001559bdc in JOIN::exec (this=0x7fff2cdde4e0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:199
随后访问:
#0  row_search_mvcc (buf=0x7fff2ccc9380 "\376\n", mode=PAGE_CUR_UNSUPP, prebuilt=0x7fff2cd4bb40, match_mode=0, direction=1)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/row/row0sel.cc:4479#1  0x00000000019b3f50 in ha_innobase::general_fetch (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n", direction=1, match_mode=0)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9425#2  0x00000000019b4261 in ha_innobase::index_next (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n")    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:9503#3  0x0000000000f680d8 in handler::ha_index_next (this=0x7fff2cd32480, buf=0x7fff2ccc9380 "\376\n") at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:3269#4  0x0000000000f719af in handler::read_range_next (this=0x7fff2cd32480) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:7612#5  0x0000000000f6f710 in handler::multi_range_read_next (this=0x7fff2cd32480, range_info=0x7ffff0359910)    at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:6614#6  0x0000000000f706b7 in DsMrr_impl::dsmrr_next (this=0x7fff2cd328f0, range_info=0x7ffff0359910) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/handler.cc:7019#7  0x00000000019c6210 in ha_innobase::multi_range_read_next (this=0x7fff2cd32480, range_info=0x7ffff0359910)    at /root/mysql5.7.14/percona-server-5.7.14-7/storage/innobase/handler/ha_innodb.cc:21372#8  0x00000000017904b2 in QUICK_RANGE_SELECT::get_next (this=0x7fff2ccc9760) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/opt_range.cc:11171#9  0x00000000014c5f56 in rr_quick (info=0x7fff2cddf050) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/records.cc:398#10 0x000000000155c397 in sub_select (join=0x7fff2cdde4e0, qep_tab=0x7fff2cddf000, end_of_records=false)    at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:1274#11 0x000000000155bd06 in do_select (join=0x7fff2cdde4e0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:944#12 0x0000000001559bdc in JOIN::exec (this=0x7fff2cdde4e0) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/sql_executor.cc:199

断点：row_search_mvcc

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