use*_*856 2 mysql innodb mysql-5.5 temporary-tables
我有一个查询，在运行它之后，如果我在同一个会话中运行显示状态，如下所示
show status 其中变量名 like '%Created_tmp_disk_tables%';
它增加了一个值。所以这意味着临时表是在磁盘上创建的吗？不确定它是否正确。
但是，如果我为该查询启用分析。下面是我得到的状态。
| status | duration |
|---------------------- |---------- |
| starting | 0.000246 |
| checking permissions | 0.000035 |
| Opening tables | 0.000098 |
| System lock | 0.000044 |
| init | 0.000209 |
| optimizing | 0.000075 |
| statistics | 0.000336 |
| preparing | 0.000138 |
| Creating tmp table | 0.000435 |
| executing | 0.000038 |
| Copying to tmp table | 2.923929 |
| Sorting result | 0.267926 |
| Sending data | 0.000945 |
| end | 0.000071 |
| removing tmp table | 0.077263 |
| query end | 0.000022 |
| closing tables | 0.000055 |
| freeing items | 0.000092 |
| logging slow query | 0.000074 |
| cleaning up | 0.000022 |在这里我找到了Copying to tmp table但没有Copying to tmp table on disk。
为什么这两者之间会发生冲突？
Show status 变量是否正确或 profiling 是否正确？
需要知道是否在磁盘上创建了临时表。
Created_tmp_disk_tables在会话或全局范围内使用变量来了解您何时在磁盘上创建了隐式临时表：
MariaDB [(none)]> SHOW STATUS like 'Created\_tmp%';
+-------------------------+-------+
| Variable_name | Value |
+-------------------------+-------+
| Created_tmp_disk_tables | 0 |
| Created_tmp_files | 6 |
| Created_tmp_tables | 0 | <--- session starts with 0 tmp tables
+-------------------------+-------+
3 rows in set (0.01 sec)
MariaDB [(none)]> SELECT 1 UNION SELECT 1;
+---+
| 1 |
+---+
| 1 |
+---+
1 row in set (0.00 sec)
MariaDB [(none)]> SHOW STATUS like 'Created\_tmp%';
+-------------------------+-------+
| Variable_name | Value |
+-------------------------+-------+
| Created_tmp_disk_tables | 0 |
| Created_tmp_files | 6 |
| Created_tmp_tables | 1 | <--- one tmp table created, 0 on disk
+-------------------------+-------+
3 rows in set (0.01 sec)
MariaDB [(none)]> SELECT 1 UNION ALL SELECT 1;
+---+
| 1 |
+---+
| 1 |
| 1 |
+---+
2 rows in set (0.00 sec)
MariaDB [(none)]> SHOW STATUS like 'Created\_tmp%';
+-------------------------+-------+
| Variable_name | Value |
+-------------------------+-------+
| Created_tmp_disk_tables | 0 |
| Created_tmp_files | 6 |
| Created_tmp_tables | 1 | <--- no tmp table created
+-------------------------+-------+
3 rows in set (0.00 sec)
MariaDB [(none)]> create table test.test (a blob);
Query OK, 0 rows affected (0.18 sec)
MariaDB [(none)]> SELECT * FROM test.test UNION SELECT * FROM test.test;
Empty set (0.00 sec)
MariaDB [(none)]> SHOW STATUS like 'Created\_tmp%';
+-------------------------+-------+
| Variable_name | Value |
+-------------------------+-------+
| Created_tmp_disk_tables | 1 | <--- tmp table created on disk
| Created_tmp_files | 6 |
| Created_tmp_tables | 2 |
+-------------------------+-------+
3 rows in set (0.00 sec)
如果您启用performance_schema，默认配置（非常非常低的开销）会为您提供您可能需要的所有内容的摘要：
MariaDB [(none)]> SELECT * FROM performance_schema.events_statements_summary_by_digest\G
[...]
*************************** 26. row ***************************
SCHEMA_NAME: test
DIGEST: f0aad09130b2e108d8dd1c58d1713678
DIGEST_TEXT: SELECT * FROM `test` UNION SELECT * FROM `test`
COUNT_STAR: 1
SUM_TIMER_WAIT: 716448000
MIN_TIMER_WAIT: 716448000
AVG_TIMER_WAIT: 716448000
MAX_TIMER_WAIT: 716448000
SUM_LOCK_TIME: 308000000
SUM_ERRORS: 0
SUM_WARNINGS: 0
SUM_ROWS_AFFECTED: 0
SUM_ROWS_SENT: 0
SUM_ROWS_EXAMINED: 0
SUM_CREATED_TMP_DISK_TABLES: 1 <---- 1 disk tmp table created
SUM_CREATED_TMP_TABLES: 1 <---- 1 tmp table created (including the disk one)
SUM_SELECT_FULL_JOIN: 0
SUM_SELECT_FULL_RANGE_JOIN: 0
SUM_SELECT_RANGE: 0
SUM_SELECT_RANGE_CHECK: 0
SUM_SELECT_SCAN: 3
SUM_SORT_MERGE_PASSES: 0
SUM_SORT_RANGE: 0
SUM_SORT_ROWS: 0
SUM_SORT_SCAN: 0
SUM_NO_INDEX_USED: 1
SUM_NO_GOOD_INDEX_USED: 0
FIRST_SEEN: 2018-01-06 21:18:18
LAST_SEEN: 2018-01-06 21:18:18
编辑：我刚刚注意到你仍然在 5.5- 我强烈建议升级，只有 P_S 值得在调试时不丢失。现在，会话/全局变量应该对你有用，分析也不会工作：
MariaDB [(none)]> SET profiling = 1;
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> SELECT * FROM test.test UNION SELECT * FROM test.test;
Empty set (0.00 sec)
MariaDB [(none)]> SHOW PROFILES;
+----------+------------+-------------------------------------------------------+
| Query_ID | Duration | Query |
+----------+------------+-------------------------------------------------------+
| 1 | 0.00055224 | SELECT * FROM test.test UNION SELECT * FROM test.test |
+----------+------------+-------------------------------------------------------+
1 row in set (0.00 sec)
MariaDB [(none)]> SHOW PROFILE FOR QUERY 1;
+----------------------+----------+
| Status | Duration |
+----------------------+----------+
| starting | 0.000053 |
| checking permissions | 0.000011 |
| checking permissions | 0.000007 |
| Opening tables | 0.000026 |
| After opening tables | 0.000009 |
| System lock | 0.000008 |
| Table lock | 0.000196 |
| optimizing | 0.000010 |
| statistics | 0.000015 |
| preparing | 0.000013 |
| optimizing | 0.000007 |
| statistics | 0.000006 |
| preparing | 0.000009 |
| executing | 0.000005 |
| Sending data | 0.000019 |
| executing | 0.000004 |
| Sending data | 0.000009 |
| optimizing | 0.000006 |
| statistics | 0.000006 |
| preparing | 0.000005 |
| executing | 0.000004 |
| Sending data | 0.000016 |
| removing tmp table | 0.000057 |
| Sending data | 0.000006 |
| query end | 0.000008 |
| closing tables | 0.000004 |
| Unlocking tables | 0.000008 |
| freeing items | 0.000005 |
| updating status | 0.000009 |
| cleaning up | 0.000012 |
+----------------------+----------+
30 rows in set (0.00 sec)
有时你会看到一个类似于“从堆复制到 myisam”的步骤，当它依赖内存执行时，但不会每次都发生，如上所示。您在标签上提到了 innodb ，但隐式临时表仅从5.7开始成为 InnoDB (vs HEAP + MyISAM) 。
| 归档时间： |
|
| 查看次数： |
5223 次 |
| 最近记录： |