事务处理对持久统计信息自动收集的影响
1. 持久化统计信息
持久统计信息将统计信息存储到磁盘，使它们在服务器重启后保持不变，优化器更有可能在查询时做出一致的选择，从而提高执行计划的稳定性。
在innodb_stats_persistent=ON（默认值）或表定义使用 stats_persistent=1时，优化器统计信息会持久化保存。
持久统计信息存储在 mysql.innodb_table_stats 和 mysql.innodb_index_stats 表中，last_update 列可以看到上次更新统计信息的时间。
系统变量innodb_stats_auto_recalc（默认ON）控制表行更改超过10%时，是否自动计算统计信息。也可以通过创建或更改表时指定stats_auto_recalc子句为单个表配置自动统计重新计算。
由于自动统计信息收集是一个后台线程，其处理过程与DML操作是异步的，在DML操作超过 10% 的表后，可能不会立即重新计算统计信息。在某些情况下，统计数据重新计算可能会延迟几秒钟。如果立即需要最新的统计信息，执行 ANALYZE TABLE 以启动统计信息的同步计算。
事务的 commit 和 rollback 会影响统计信息的自动收集么？通过下面测试，可以回答这问题。
2. 测试commit和rollback对持久统计信息收集的影响
测试环境的系统变量值：
greatsql> SHOW GLOBAL VARIABLES LIKE 'innodb_stats%';
+--------------------------------------+-------------+
| Variable_name | Value |
+--------------------------------------+-------------+
| innodb_stats_auto_recalc | ON |
| innodb_stats_include_delete_marked | OFF |
| innodb_stats_method | nulls_equal |
| innodb_stats_on_metadata | OFF |
| innodb_stats_persistent | ON |
| innodb_stats_persistent_sample_pages | 20 |
| innodb_stats_transient_sample_pages | 8 |
+--------------------------------------+-------------+2.1 INSERT 操作
greatsql> TRUNCATE TABLE test1;
Query OK, 0 rows affected (0.05 sec)
-- 开启事务，在空表test1中插入10万行数据
greatsql> BEGIN;
Query OK, 0 rows affected (0.00 sec)
greatsql> SELECT now();INSERT INTO test1 SELECT * FROM LIMIT 100000;SELECT now();
+---------------------+
| now() |
+---------------------+
| 2025-01-07 09:59:19 |
+---------------------+
1 row in set (0.00 sec)
Query OK, 100000 rows affected (2.73 sec)
Records: 100000 Duplicates: 0 Warnings: 0
+---------------------+
| now() |
+---------------------+
| 2025-01-07 09:59:21 |
+---------------------+
1 row in set (0.00 sec)
-- 事务没有提交，但统计信息已收集
greatsql> SELECT * FROM mysql.innodb_index_stats WHERE database_name='testdb1' AND table_name='test1';
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| database_name | table_name | index_name | last_update | stat_name | stat_value | sample_size | stat_description |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| testdb1 | test1 | PRIMARY | 2025-01-07 09:59:19 | n_diff_pfx01 | 11 | 1 | id |
| testdb1 | test1 | PRIMARY | 2025-01-07 09:59:19 | n_leaf_pages | 1 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | PRIMARY | 2025-01-07 09:59:19 | size | 1 | NULL | Number of pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 09:59:19 | n_diff_pfx01 | 11 | 1 | k |
| testdb1 | test1 | k_1 | 2025-01-07 09:59:19 | n_diff_pfx02 | 11 | 1 | k,id |
| testdb1 | test1 | k_1 | 2025-01-07 09:59:19 | n_leaf_pages | 1 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 09:59:19 | size | 1 | NULL | Number of pages in the index |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
7 rows in set (0.00 sec)
greatsql> SELECT * FROM mysql.innodb_index_stats WHERE database_name='testdb1' AND table_name='test1';
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| database_name | table_name | index_name | last_update | stat_name | stat_value | sample_size | stat_description |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| testdb1 | test1 | PRIMARY | 2025-01-07 09:59:29 | n_diff_pfx01 | 98712 | 20 | id |
| testdb1 | test1 | PRIMARY | 2025-01-07 09:59:29 | n_leaf_pages | 1371 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | PRIMARY | 2025-01-07 09:59:29 | size | 1379 | NULL | Number of pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 09:59:29 | n_diff_pfx01 | 30169 | 20 | k |
| testdb1 | test1 | k_1 | 2025-01-07 09:59:29 | n_diff_pfx02 | 100268 | 20 | k,id |
| testdb1 | test1 | k_1 | 2025-01-07 09:59:29 | n_leaf_pages | 128 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 09:59:29 | size | 161 | NULL | Number of pages in the index |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
7 rows in set (0.00 sec)
-- 回滚事务
greatsql> ROLLBACK;
Query OK, 0 rows affected (2.64 sec)
-- 没有重新收集统计信息，统计信息与表数据不匹配
greatsql> SELECT * FROM mysql.innodb_index_stats WHERE database_name='testdb1' AND table_name='test1';
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| database_name | table_name | index_name | last_update | stat_name | stat_value | sample_size | stat_description |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| testdb1 | test1 | PRIMARY | 2025-01-07 09:59:29 | n_diff_pfx01 | 98712 | 20 | id |
| testdb1 | test1 | PRIMARY | 2025-01-07 09:59:29 | n_leaf_pages | 1371 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | PRIMARY | 2025-01-07 09:59:29 | size | 1379 | NULL | Number of pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 09:59:29 | n_diff_pfx01 | 30169 | 20 | k |
| testdb1 | test1 | k_1 | 2025-01-07 09:59:29 | n_diff_pfx02 | 100268 | 20 | k,id |
| testdb1 | test1 | k_1 | 2025-01-07 09:59:29 | n_leaf_pages | 128 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 09:59:29 | size | 161 | NULL | Number of pages in the index |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
7 rows in set (0.00 sec)
greatsql> SELECT COUNT(*) FROM test1;
+----------+
| count(*) |
+----------+
| 0 |
+----------+
1 row in set (0.00 sec)
-- analyze重新收集统计信息，统计信息才和表数据一致
greatsql> ANALYZE TABLE test1;
+---------------+---------+----------+----------+
| Table | Op | Msg_type | Msg_text |
+---------------+---------+----------+----------+
| testdb1.test1 | analyze | status | OK |
+---------------+---------+----------+----------+
1 row in set (0.06 sec)
greatsql> SELECT * FROM mysql.innodb_index_stats WHERE database_name='testdb1' AND table_name='test1';
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| database_name | table_name | index_name | last_update | stat_name | stat_value | sample_size | stat_description |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| testdb1 | test1 | PRIMARY | 2025-01-07 10:01:58 | n_diff_pfx01 | 0 | 1 | id |
| testdb1 | test1 | PRIMARY | 2025-01-07 10:01:58 | n_leaf_pages | 1 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | PRIMARY | 2025-01-07 10:01:58 | size | 1 | NULL | Number of pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 10:01:58 | n_diff_pfx01 | 0 | 1 | k |
| testdb1 | test1 | k_1 | 2025-01-07 10:01:58 | n_diff_pfx02 | 0 | 1 | k,id |
| testdb1 | test1 | k_1 | 2025-01-07 10:01:58 | n_leaf_pages | 1 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 10:01:58 | size | 1 | NULL | Number of pages in the index |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
7 rows in set (0.00 sec)2.2 DELETE 操作
greatsql> SELECT COUNT(*) FROM test1;
+----------+
| count(*) |
+----------+
| 100000 |
+----------+
1 row in set (0.15 sec)
-- 开启事务，执行delete操作
greatsql> BEGIN;
Query OK, 0 rows affected (0.00 sec)
greatsql> SELECT now();DELETE FROM test1;SELECT now();
+---------------------+
| now() |
+---------------------+
| 2025-01-07 09:41:36 |
+---------------------+
1 row in set (0.00 sec)
Query OK, 100000 rows affected (1.87 sec)
+---------------------+
| now() |
+---------------------+
| 2025-01-07 09:41:38 |
+---------------------+
1 row in set (0.00 sec)
-- 在delete开始时，进行了一次统计信息收集
greatsql> SELECT * FROM mysql.innodb_index_stats WHERE database_name='testdb1' AND table_name='test1';
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| database_name | table_name | index_name | last_update | stat_name | stat_value | sample_size | stat_description |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| testdb1 | test1 | PRIMARY | 2025-01-07 09:41:36 | n_diff_pfx01 | 98712 | 20 | id |
| testdb1 | test1 | PRIMARY | 2025-01-07 09:41:36 | n_leaf_pages | 1371 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | PRIMARY | 2025-01-07 09:41:36 | size | 1379 | NULL | Number of pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 09:41:36 | n_diff_pfx01 | 32313 | 20 | k |
| testdb1 | test1 | k_1 | 2025-01-07 09:41:36 | n_diff_pfx02 | 99244 | 20 | k,id |
| testdb1 | test1 | k_1 | 2025-01-07 09:41:36 | n_leaf_pages | 128 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 09:41:36 | size | 161 | NULL | Number of pages in the index |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
7 rows in set (0.00 sec)
-- delete完成一段时间后（约10秒）进行了第二次统计信息收集
greatsql> SELECT * FROM mysql.innodb_index_stats WHERE database_name='testdb1' AND table_name='test1';
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| database_name | table_name | index_name | last_update | stat_name | stat_value | sample_size | stat_description |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| testdb1 | test1 | PRIMARY | 2025-01-07 09:41:46 | n_diff_pfx01 | 0 | 20 | id |
| testdb1 | test1 | PRIMARY | 2025-01-07 09:41:46 | n_leaf_pages | 1371 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | PRIMARY | 2025-01-07 09:41:46 | size | 1379 | NULL | Number of pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 09:41:46 | n_diff_pfx01 | 0 | 20 | k |
| testdb1 | test1 | k_1 | 2025-01-07 09:41:46 | n_diff_pfx02 | 0 | 20 | k,id |
| testdb1 | test1 | k_1 | 2025-01-07 09:41:46 | n_leaf_pages | 128 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 09:41:46 | size | 161 | NULL | Number of pages in the index |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
7 rows in set (0.00 sec)
-- 回滚事务
greatsql> ROLLBACK;
Query OK, 0 rows affected (1.95 sec)
-- 事务回滚后，统计信息与表数据不匹配
greatsql> SELECT * FROM mysql.innodb_index_stats WHERE database_name='testdb1' AND table_name='test1';
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| database_name | table_name | index_name | last_update | stat_name | stat_value | sample_size | stat_description |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| testdb1 | test1 | PRIMARY | 2025-01-07 09:41:46 | n_diff_pfx01 | 0 | 20 | id |
| testdb1 | test1 | PRIMARY | 2025-01-07 09:41:46 | n_leaf_pages | 1371 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | PRIMARY | 2025-01-07 09:41:46 | size | 1379 | NULL | Number of pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 09:41:46 | n_diff_pfx01 | 0 | 20 | k |
| testdb1 | test1 | k_1 | 2025-01-07 09:41:46 | n_diff_pfx02 | 0 | 20 | k,id |
| testdb1 | test1 | k_1 | 2025-01-07 09:41:46 | n_leaf_pages | 128 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 09:41:46 | size | 161 | NULL | Number of pages in the index |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
7 rows in set (0.00 sec)
greatsql> SELECT COUNT(*) FROM test1;
+----------+
| count(*) |
+----------+
| 100000 |
+----------+
1 row in set (0.15 sec)
-- analyze重新收集统计信息，统计信息才和表数据一致
greatsql> ANALYZE TABLE test1;
+---------------+---------+----------+----------+
| Table | Op | Msg_type | Msg_text |
+---------------+---------+----------+----------+
| testdb1.test1 | analyze | status | OK |
+---------------+---------+----------+----------+
1 row in set (0.08 sec)
greatsql> SELECT * FROM mysql.innodb_index_stats WHERE database_name='testdb1' AND table_name='test1';
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| database_name | table_name | index_name | last_update | stat_name | stat_value | sample_size | stat_description |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
| testdb1 | test1 | PRIMARY | 2025-01-07 09:47:29 | n_diff_pfx01 | 98712 | 20 | id |
| testdb1 | test1 | PRIMARY | 2025-01-07 09:47:29 | n_leaf_pages | 1371 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | PRIMARY | 2025-01-07 09:47:29 | size | 1379 | NULL | Number of pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 09:47:29 | n_diff_pfx01 | 32332 | 20 | k |
| testdb1 | test1 | k_1 | 2025-01-07 09:47:29 | n_diff_pfx02 | 100051 | 20 | k,id |
| testdb1 | test1 | k_1 | 2025-01-07 09:47:29 | n_leaf_pages | 128 | NULL | Number of leaf pages in the index |
| testdb1 | test1 | k_1 | 2025-01-07 09:47:29 | size | 161 | NULL | Number of pages in the index |
+---------------+------------+------------+---------------------+--------------+------------+-------------+-----------------------------------+
7 rows in set (0.01 sec)3. 总结
- 数据量变化大（超过10%）的DML操作会导致2次统计信息收集，一次是DML开始时，一次是DML完成约10秒后。
- DML操作是否
COMMIT提交，不影响统计信息收集。 - DML操作的
rollback回滚，可能造成统计信息与表数据不一致。当大数据DML操作回滚后，可以执行ANALYZE TABLE重新收集表的统计信息。
Enjoy GreatSQL :)
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