MySQL 8.0 按表现分组
MySQL 8.0 Group by Performance
为了比较 MySQL 5.7 和 8.0，我使用 sysbench 创建了一个 table。
我尝试了测试。服务器性能完全一样
结果，oltp_point_select 表现出几乎相似的性能。
但是，在进行下面的分组测试时，MySQL 8.0 显示出 10 倍的性能。
但是不知道为什么这么快。
我不知道是否可以找到 MySQL 8.0 发行说明。
在 8.0 中，谁能告诉我为什么 group by 更快？
0。 table 架构
CREATE TABLE `sbtest2` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`k` int(11) NOT NULL DEFAULT '0',
`c` char(120) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',
`pad` char(60) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',
PRIMARY KEY (`id`),
KEY `k_2` (`k`),
KEY `idx1` (`k`,`pad`)
) ENGINE=InnoDB AUTO_INCREMENT=1099289 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
1. MySQL 5.7
服务器版本：5.7.17-log 源码分布
5.7 结果
testdb 17:24:38 > select count(0),pad from sbtest2 where k between 400000 and 600000 group by pad limit 1;
+----------+-------------------------------------------------------------+
| count(0) | pad |
+----------+-------------------------------------------------------------+
| 1 | 00000012813-73478546096-60491222567-55128816668-26346684571 |
+----------+-------------------------------------------------------------+
**1 row in set (21.88 sec)**
testdb 17:21:30 > explain select count(0),pad from sbtest2 where k between 400000 and 600000 group by pad limit 10\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: sbtest2
partitions: NULL
type: range
possible_keys: k_2,idx1
key: idx1
key_len: 4
ref: NULL
rows: 493200
filtered: 100.00
Extra: Using where; Using index; Using temporary; Using filesort
1 row in set, 1 warning (0.00 sec)
17:55:17 > show profile;
+---------------------------+-----------+
| Status | Duration |
+---------------------------+-----------+
| starting | 0.000083 |
| checking permissions | 0.000008 |
| Opening tables | 0.000017 |
| init | 0.000032 |
| System lock | 0.000013 |
| optimizing | 0.000010 |
| statistics | 0.076138 |
| preparing | 0.000018 |
| Creating tmp table | 0.000033 |
| Sorting result | 0.000005 |
| executing | 0.000003 |
| Sending data | 2.790353 |
| converting HEAP to ondisk | 1.709809 |
| Sending data | 14.403732 |
| Creating sort index | 2.236432 |
| end | 0.000014 |
| query end | 0.000012 |
| removing tmp table | 0.017293 |
| query end | 0.000007 |
| closing tables | 0.000011 |
| freeing items | 0.000252 |
| logging slow query | 0.000055 |
| cleaning up | 0.000014 |
+---------------------------+-----------+
2。 MySQL8.0
服务器版本：8.0.11 MySQL 社区服务器 - GPL
结果
testdb 17:24:24 > select count(0),pad from sbtest2 where k between 400000 and 600000 group by pad limit 1;
+----------+-------------------------------------------------------------+
| count(0) | pad |
+----------+-------------------------------------------------------------+
| 1 | 30506873183-39276415649-14634764539-17515472140-54546407224 |
+----------+-------------------------------------------------------------+
**1 row in set (2.32 sec)**
testdb 17:23:29 > explain select count(0),pad from sbtest2 where k between 400000 and 600000 group by pad limit 10\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: sbtest2
partitions: NULL
type: range
possible_keys: k_2,idx1
key: idx1
key_len: 4
ref: NULL
rows: 493200
filtered: 100.00
Extra: Using where; Using index; Using temporary
1 row in set, 1 warning (0.04 sec)
testdb 17:55:00 > show profile;
+----------------------+----------+
| Status | Duration |
+----------------------+----------+
| starting | 0.000103 |
| checking permissions | 0.000018 |
| Opening tables | 0.000051 |
| init | 0.000008 |
| System lock | 0.000013 |
| optimizing | 0.000010 |
| statistics | 0.000144 |
| preparing | 0.000024 |
| Creating tmp table | 0.000042 |
| executing | 0.000004 |
| Sending data | 2.407031 |
| end | 0.000018 |
| query end | 0.000019 |
| removing tmp table | 0.087750 |
| query end | 0.000020 |
| closing tables | 0.000018 |
| freeing items | 0.000193 |
| logging slow query | 0.000061 |
| cleaning up | 0.000015 |
+----------------------+----------+
@Rick James
5.7 的 sbtest2 table 被转储并应用于 8.0。
现在两个table完全一样了
5_7.testdb 18:25:13 > select @@version;
+------------+
| @@version |
+------------+
| 5.7.17-log |
+------------+
1 row in set (0.00 sec)
5_7.testdb 18:25:16 > select count(*) from sbtest2;
+----------+
| count(*) |
+----------+
| 1099288 |
+----------+
1 row in set (0.17 sec)
5_7.testdb 18:25:22 > select count(0),pad from sbtest2 where k between 400000 and 500000 group by pad order by pad limit 1;
+----------+-------------------------------------------------------------+
| count(0) | pad |
+----------+-------------------------------------------------------------+
| 1 | 00000012813-73478546096-60491222567-55128816668-26346684571 |
+----------+-------------------------------------------------------------+
1 row in set (7.34 sec)
5_7.testdb 18:26:15 > explain select count(0),pad from sbtest2 where k between 400000 and 500000 group by pad order by pad limit 1;
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-----------------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-----------------------------------------------------------+
| 1 | SIMPLE | sbtest2 | NULL | range | k_2,idx1 | idx1 | 4 | NULL | 542160 | 100.00 | Using where; Using index; Using temporary; Using filesort |
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-----------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)
Note (Code 1003): /* select#1 */ select count(0) AS `count(0)`,`testdb`.`sbtest2`.`pad` AS `pad` from `testdb`.`sbtest2` where (`testdb`.`sbtest2`.`k` between 400000 and 500000) group by `testdb`.`sbtest2`.`pad` order by `testdb`.`sbtest2`.`pad` limit 1
5_7.testdb 18:26:27 > explain format=json select count(0),pad from sbtest2 where k between 400000 and 500000 group by pad order by pad limit 1;
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| {
"query_block": {
"select_id": 1,
"cost_info": {
"query_cost": "232810.86"
},
"ordering_operation": {
"using_filesort": false,
"grouping_operation": {
"using_temporary_table": true,
"using_filesort": true,
"table": {
"table_name": "sbtest2",
"access_type": "range",
"possible_keys": [
"k_2",
"idx1"
],
"key": "idx1",
"used_key_parts": [
"k"
],
"key_length": "4",
"rows_examined_per_scan": 542160,
"rows_produced_per_join": 542160,
"filtered": "100.00",
"using_index": true,
"cost_info": {
"read_cost": "124378.86",
"eval_cost": "108432.00",
"prefix_cost": "232810.86",
"data_read_per_join": "380M"
},
"used_columns": [
"id",
"k",
"pad"
],
"attached_condition": "(`testdb`.`sbtest2`.`k` between 400000 and 500000)"
}
}
}
}
} |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)
8.0
8_0.testdb 18:25:00 > select @@version;
+-----------+
| @@version |
+-----------+
| 8.0.11 |
+-----------+
1 row in set (0.00 sec)
8_0.testdb 18:25:25 > select count(*) from sbtest2;
+----------+
| count(*) |
+----------+
| 1099288 |
+----------+
1 row in set (0.16 sec)
8_0.testdb 18:25:29 > select count(0),pad from sbtest2 where k between 400000 and 500000 group by pad order by pad limit 1;
+----------+-------------------------------------------------------------+
| count(0) | pad |
+----------+-------------------------------------------------------------+
| 1 | 00000012813-73478546096-60491222567-55128816668-26346684571 |
+----------+-------------------------------------------------------------+
1 row in set (1.27 sec)
8_0.testdb 18:26:04 > explain select count(0),pad from sbtest2 where k between 400000 and 500000 group by pad order by pad limit 1;
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-----------------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-----------------------------------------------------------+
| 1 | SIMPLE | sbtest2 | NULL | range | k_2,idx1 | idx1 | 4 | NULL | 503160 | 100.00 | Using where; Using index; Using temporary; Using filesort |
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-----------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)
Note (Code 1003): /* select#1 */ select count(0) AS `count(0)`,`testdb`.`sbtest2`.`pad` AS `pad` from `testdb`.`sbtest2` where (`testdb`.`sbtest2`.`k` between 400000 and 500000) group by `testdb`.`sbtest2`.`pad` order by `testdb`.`sbtest2`.`pad` limit 1
8_0.testdb 18:26:23 > explain format=json select count(0),pad from sbtest2 where k between 400000 and 500000 group by pad order by pad limit 1;
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| {
"query_block": {
"select_id": 1,
"cost_info": {
"query_cost": "104331.96"
},
"ordering_operation": {
"using_filesort": false,
"grouping_operation": {
"using_temporary_table": true,
"using_filesort": true,
"table": {
"table_name": "sbtest2",
"access_type": "range",
"possible_keys": [
"k_2",
"idx1"
],
"key": "idx1",
"used_key_parts": [
"k"
],
"key_length": "4",
"rows_examined_per_scan": 503160,
"rows_produced_per_join": 503160,
"filtered": "100.00",
"using_index": true,
"cost_info": {
"read_cost": "54015.96",
"eval_cost": "50316.00",
"prefix_cost": "104331.96",
"data_read_per_join": "353M"
},
"used_columns": [
"id",
"k",
"pad"
],
"attached_condition": "(`testdb`.`sbtest2`.`k` between 400000 and 500000)"
}
}
}
}
} |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)
MySQL 8.0 使用新的存储引擎 TempTable，用于内部临时 tables。 （有关详细信息，请参阅 MySQL Manual。）此引擎没有每个 table 的最大内存限制，而是所有内部 table 的公共内存池。它也有自己的溢出到磁盘机制，不会像早期版本那样溢出到InnoDB或MyISAM。
5.7 的配置文件包含 "converting HEAP to ondisk"。这意味着 table 达到了 MEMORY 引擎的最大 table 大小（默认为 16 MB）并且数据被传输到 InnoDB。之后的大部分时间都花在访问 InnoDB 中的临时 table 上。在 MySQL 8.0 中，临时 tables 的内存池默认大小为 1 GB，因此在这种情况下可能不会溢出到磁盘。
为了比较 MySQL 5.7 和 8.0，我使用 sysbench 创建了一个 table。 我尝试了测试。服务器性能完全一样 结果，oltp_point_select 表现出几乎相似的性能。
但是，在进行下面的分组测试时，MySQL 8.0 显示出 10 倍的性能。 但是不知道为什么这么快。
我不知道是否可以找到 MySQL 8.0 发行说明。 在 8.0 中，谁能告诉我为什么 group by 更快？
0。 table 架构
CREATE TABLE `sbtest2` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`k` int(11) NOT NULL DEFAULT '0',
`c` char(120) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',
`pad` char(60) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',
PRIMARY KEY (`id`),
KEY `k_2` (`k`),
KEY `idx1` (`k`,`pad`)
) ENGINE=InnoDB AUTO_INCREMENT=1099289 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
1. MySQL 5.7 服务器版本：5.7.17-log 源码分布
5.7 结果
testdb 17:24:38 > select count(0),pad from sbtest2 where k between 400000 and 600000 group by pad limit 1;
+----------+-------------------------------------------------------------+
| count(0) | pad |
+----------+-------------------------------------------------------------+
| 1 | 00000012813-73478546096-60491222567-55128816668-26346684571 |
+----------+-------------------------------------------------------------+
**1 row in set (21.88 sec)**
testdb 17:21:30 > explain select count(0),pad from sbtest2 where k between 400000 and 600000 group by pad limit 10\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: sbtest2
partitions: NULL
type: range
possible_keys: k_2,idx1
key: idx1
key_len: 4
ref: NULL
rows: 493200
filtered: 100.00
Extra: Using where; Using index; Using temporary; Using filesort
1 row in set, 1 warning (0.00 sec)
17:55:17 > show profile;
+---------------------------+-----------+
| Status | Duration |
+---------------------------+-----------+
| starting | 0.000083 |
| checking permissions | 0.000008 |
| Opening tables | 0.000017 |
| init | 0.000032 |
| System lock | 0.000013 |
| optimizing | 0.000010 |
| statistics | 0.076138 |
| preparing | 0.000018 |
| Creating tmp table | 0.000033 |
| Sorting result | 0.000005 |
| executing | 0.000003 |
| Sending data | 2.790353 |
| converting HEAP to ondisk | 1.709809 |
| Sending data | 14.403732 |
| Creating sort index | 2.236432 |
| end | 0.000014 |
| query end | 0.000012 |
| removing tmp table | 0.017293 |
| query end | 0.000007 |
| closing tables | 0.000011 |
| freeing items | 0.000252 |
| logging slow query | 0.000055 |
| cleaning up | 0.000014 |
+---------------------------+-----------+
2。 MySQL8.0 服务器版本：8.0.11 MySQL 社区服务器 - GPL
结果
testdb 17:24:24 > select count(0),pad from sbtest2 where k between 400000 and 600000 group by pad limit 1;
+----------+-------------------------------------------------------------+
| count(0) | pad |
+----------+-------------------------------------------------------------+
| 1 | 30506873183-39276415649-14634764539-17515472140-54546407224 |
+----------+-------------------------------------------------------------+
**1 row in set (2.32 sec)**
testdb 17:23:29 > explain select count(0),pad from sbtest2 where k between 400000 and 600000 group by pad limit 10\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: sbtest2
partitions: NULL
type: range
possible_keys: k_2,idx1
key: idx1
key_len: 4
ref: NULL
rows: 493200
filtered: 100.00
Extra: Using where; Using index; Using temporary
1 row in set, 1 warning (0.04 sec)
testdb 17:55:00 > show profile;
+----------------------+----------+
| Status | Duration |
+----------------------+----------+
| starting | 0.000103 |
| checking permissions | 0.000018 |
| Opening tables | 0.000051 |
| init | 0.000008 |
| System lock | 0.000013 |
| optimizing | 0.000010 |
| statistics | 0.000144 |
| preparing | 0.000024 |
| Creating tmp table | 0.000042 |
| executing | 0.000004 |
| Sending data | 2.407031 |
| end | 0.000018 |
| query end | 0.000019 |
| removing tmp table | 0.087750 |
| query end | 0.000020 |
| closing tables | 0.000018 |
| freeing items | 0.000193 |
| logging slow query | 0.000061 |
| cleaning up | 0.000015 |
+----------------------+----------+
@Rick James 5.7 的 sbtest2 table 被转储并应用于 8.0。 现在两个table完全一样了
5_7.testdb 18:25:13 > select @@version;
+------------+
| @@version |
+------------+
| 5.7.17-log |
+------------+
1 row in set (0.00 sec)
5_7.testdb 18:25:16 > select count(*) from sbtest2;
+----------+
| count(*) |
+----------+
| 1099288 |
+----------+
1 row in set (0.17 sec)
5_7.testdb 18:25:22 > select count(0),pad from sbtest2 where k between 400000 and 500000 group by pad order by pad limit 1;
+----------+-------------------------------------------------------------+
| count(0) | pad |
+----------+-------------------------------------------------------------+
| 1 | 00000012813-73478546096-60491222567-55128816668-26346684571 |
+----------+-------------------------------------------------------------+
1 row in set (7.34 sec)
5_7.testdb 18:26:15 > explain select count(0),pad from sbtest2 where k between 400000 and 500000 group by pad order by pad limit 1;
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-----------------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-----------------------------------------------------------+
| 1 | SIMPLE | sbtest2 | NULL | range | k_2,idx1 | idx1 | 4 | NULL | 542160 | 100.00 | Using where; Using index; Using temporary; Using filesort |
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-----------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)
Note (Code 1003): /* select#1 */ select count(0) AS `count(0)`,`testdb`.`sbtest2`.`pad` AS `pad` from `testdb`.`sbtest2` where (`testdb`.`sbtest2`.`k` between 400000 and 500000) group by `testdb`.`sbtest2`.`pad` order by `testdb`.`sbtest2`.`pad` limit 1
5_7.testdb 18:26:27 > explain format=json select count(0),pad from sbtest2 where k between 400000 and 500000 group by pad order by pad limit 1;
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| {
"query_block": {
"select_id": 1,
"cost_info": {
"query_cost": "232810.86"
},
"ordering_operation": {
"using_filesort": false,
"grouping_operation": {
"using_temporary_table": true,
"using_filesort": true,
"table": {
"table_name": "sbtest2",
"access_type": "range",
"possible_keys": [
"k_2",
"idx1"
],
"key": "idx1",
"used_key_parts": [
"k"
],
"key_length": "4",
"rows_examined_per_scan": 542160,
"rows_produced_per_join": 542160,
"filtered": "100.00",
"using_index": true,
"cost_info": {
"read_cost": "124378.86",
"eval_cost": "108432.00",
"prefix_cost": "232810.86",
"data_read_per_join": "380M"
},
"used_columns": [
"id",
"k",
"pad"
],
"attached_condition": "(`testdb`.`sbtest2`.`k` between 400000 and 500000)"
}
}
}
}
} |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)
8.0
8_0.testdb 18:25:00 > select @@version;
+-----------+
| @@version |
+-----------+
| 8.0.11 |
+-----------+
1 row in set (0.00 sec)
8_0.testdb 18:25:25 > select count(*) from sbtest2;
+----------+
| count(*) |
+----------+
| 1099288 |
+----------+
1 row in set (0.16 sec)
8_0.testdb 18:25:29 > select count(0),pad from sbtest2 where k between 400000 and 500000 group by pad order by pad limit 1;
+----------+-------------------------------------------------------------+
| count(0) | pad |
+----------+-------------------------------------------------------------+
| 1 | 00000012813-73478546096-60491222567-55128816668-26346684571 |
+----------+-------------------------------------------------------------+
1 row in set (1.27 sec)
8_0.testdb 18:26:04 > explain select count(0),pad from sbtest2 where k between 400000 and 500000 group by pad order by pad limit 1;
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-----------------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-----------------------------------------------------------+
| 1 | SIMPLE | sbtest2 | NULL | range | k_2,idx1 | idx1 | 4 | NULL | 503160 | 100.00 | Using where; Using index; Using temporary; Using filesort |
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-----------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)
Note (Code 1003): /* select#1 */ select count(0) AS `count(0)`,`testdb`.`sbtest2`.`pad` AS `pad` from `testdb`.`sbtest2` where (`testdb`.`sbtest2`.`k` between 400000 and 500000) group by `testdb`.`sbtest2`.`pad` order by `testdb`.`sbtest2`.`pad` limit 1
8_0.testdb 18:26:23 > explain format=json select count(0),pad from sbtest2 where k between 400000 and 500000 group by pad order by pad limit 1;
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| EXPLAIN |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| {
"query_block": {
"select_id": 1,
"cost_info": {
"query_cost": "104331.96"
},
"ordering_operation": {
"using_filesort": false,
"grouping_operation": {
"using_temporary_table": true,
"using_filesort": true,
"table": {
"table_name": "sbtest2",
"access_type": "range",
"possible_keys": [
"k_2",
"idx1"
],
"key": "idx1",
"used_key_parts": [
"k"
],
"key_length": "4",
"rows_examined_per_scan": 503160,
"rows_produced_per_join": 503160,
"filtered": "100.00",
"using_index": true,
"cost_info": {
"read_cost": "54015.96",
"eval_cost": "50316.00",
"prefix_cost": "104331.96",
"data_read_per_join": "353M"
},
"used_columns": [
"id",
"k",
"pad"
],
"attached_condition": "(`testdb`.`sbtest2`.`k` between 400000 and 500000)"
}
}
}
}
} |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)
MySQL 8.0 使用新的存储引擎 TempTable，用于内部临时 tables。 （有关详细信息，请参阅 MySQL Manual。）此引擎没有每个 table 的最大内存限制，而是所有内部 table 的公共内存池。它也有自己的溢出到磁盘机制，不会像早期版本那样溢出到InnoDB或MyISAM。
5.7 的配置文件包含 "converting HEAP to ondisk"。这意味着 table 达到了 MEMORY 引擎的最大 table 大小（默认为 16 MB）并且数据被传输到 InnoDB。之后的大部分时间都花在访问 InnoDB 中的临时 table 上。在 MySQL 8.0 中，临时 tables 的内存池默认大小为 1 GB，因此在这种情况下可能不会溢出到磁盘。