为了比较MySQL 5.7和8.0，我使用sysbench创建了一个表。 我试过了这个测试。服务器的性能完全相同 结果，oltp_point_select表现出几乎相似的表现。
然而，当通过下面的测试进行分组时，MySQL 8.0的性能提高了10倍。 但我不知道为什么它很快。
我不知道是否可以找到MySQL 8.0发行说明。 在8.0中，谁会告诉我为什么分组更快？
0。表架构
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源分发
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。 MySQL 8.0 服务器版本：8.0.11 MySQL社区服务器 - GPL
RESULT
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表被转储并应用于8.0。 现在这两个表完全相同。
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)
答案 0 :(得分：6)
MySQL 8.0使用新的存储引擎TempTable作为内部临时表。 （有关详细信息，请参阅MySQL Manual。）此引擎没有每个表的最大内存限制，但是所有内部表都有一个公共内存池。它也有自己的磁盘溢出机制，并且不像早期版本那样溢出到InnoDB或MyISAM。
5.7的配置文件包含“将HEAP转换为ondisk”。这意味着表达到了MEMORY引擎的最大表大小（默认为16 MB），数据将传输到InnoDB。之后的大部分时间都花在访问InnoDB中的临时表上。在MySQL 8.0中，临时表的内存池的默认大小为1 GB，因此在这种情况下可能不会有任何磁盘溢出。