Question

我的MySQL不强，所以请原谅任何新手的错误。简短版本：

SELECT destId，count，avg FROM destAgg_geo 显着慢于来自destAgg_geo的SELECT *

prtt.destAgg是一个在dst_ip（PRIMARY）上键入的表

mysql> describe prtt.destAgg;
+---------+------------------+------+-----+---------+-------+
| Field   | Type             | Null | Key | Default | Extra |
+---------+------------------+------+-----+---------+-------+
| dst_ip  | int(10) unsigned | NO   | PRI | 0       |       |
| total   | float unsigned   | YES  |     | NULL    |       |
| avg     | float unsigned   | YES  |     | NULL    |       |
| sqtotal | float unsigned   | YES  |     | NULL    |       |
| sqavg   | float unsigned   | YES  |     | NULL    |       |
| count   | int(10) unsigned | YES  |     | NULL    |       |
+---------+------------------+------+-----+---------+-------+

geoip.blocks是一个在startIpNum和endIpNum（PRIMARY）上键入的表

mysql> describe geoip.blocks;
+------------+------------------+------+-----+---------+-------+
| Field      | Type             | Null | Key | Default | Extra |
+------------+------------------+------+-----+---------+-------+
| startIpNum | int(10) unsigned | NO   | MUL | NULL    |       |
| endIpNum   | int(10) unsigned | NO   |     | NULL    |       |
| locId      | int(10) unsigned | NO   |     | NULL    |       |
+------------+------------------+------+-----+---------+-------+

destAgg_geo是一个视图：

CREATE VIEW destAgg_geo AS SELECT * FROM destAgg JOIN geoip.blocks 
  ON destAgg.dst_ip BETWEEN geoip.blocks.startIpNum AND geoip.blocks.endIpNum;

以下是select *：

的优化计划

mysql> explain select * from destAgg_geo;
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+
| id | select_type | table   | type | possible_keys | key  | key_len | ref  | rows    | Extra                                          |
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+
|  1 | SIMPLE      | blocks  | ALL  | start_end     | NULL | NULL    | NULL | 3486646 |                                                |
|  1 | SIMPLE      | destAgg | ALL  | PRIMARY       | NULL | NULL    | NULL |  101893 | Range checked for each record (index map: 0x1) |
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+

以下是具有特定列的select的优化计划：

mysql> explain select locId,count,avg from destAgg_geo;
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+
| id | select_type | table   | type | possible_keys | key  | key_len | ref  | rows    | Extra                                          |
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+
|  1 | SIMPLE      | destAgg | ALL  | PRIMARY       | NULL | NULL    | NULL |  101893 |                                                |
|  1 | SIMPLE      | blocks  | ALL  | start_end     | NULL | NULL    | NULL | 3486646 | Range checked for each record (index map: 0x1) |
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+

以下是来自destAgg的每一列的优化计划，以及geoip.blocks中的locId列：

mysql> explain select dst_ip,total,avg,sqtotal,sqavg,count,locId from destAgg_geo;
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+
| id | select_type | table   | type | possible_keys | key  | key_len | ref  | rows    | Extra                                          |
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+
|  1 | SIMPLE      | blocks  | ALL  | start_end     | NULL | NULL    | NULL | 3486646 |                                                |
|  1 | SIMPLE      | destAgg | ALL  | PRIMARY       | NULL | NULL    | NULL |  101893 | Range checked for each record (index map: 0x1) |
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+

删除除dst_ip以外的所有列，范围检查翻转到块：

mysql> explain select dst_ip,avg,sqtotal,sqavg,count,locId from destAgg_geo;
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+
| id | select_type | table   | type | possible_keys | key  | key_len | ref  | rows    | Extra                                          |
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+
|  1 | SIMPLE      | destAgg | ALL  | PRIMARY       | NULL | NULL    | NULL |  101893 |                                                |
|  1 | SIMPLE      | blocks  | ALL  | start_end     | NULL | NULL    | NULL | 3486646 | Range checked for each record (index map: 0x1) |
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+

然后慢得多。这是怎么回事？

（是的，我可以从那里使用*查询结果和处理，但我想知道发生了什么以及为什么）

编辑 - 解析VIEW查询：

mysql> explain SELECT * FROM destAgg JOIN geoip.blocks ON destAgg.dst_ip BETWEEN geoip.blocks.startIpNum AND geoip.blocks.endIpNum;
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+
| id | select_type | table   | type | possible_keys | key  | key_len | ref  | rows    | Extra                                          |
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+
|  1 | SIMPLE      | blocks  | ALL  | start_end     | NULL | NULL    | NULL | 3486646 |                                                |
|  1 | SIMPLE      | destAgg | ALL  | PRIMARY       | NULL | NULL    | NULL |  101893 | Range checked for each record (index map: 0x1) |
+----+-------------+---------+------+---------------+------+---------+------+---------+------------------------------------------------+

Answer 1

MySQL可以告诉您是否在两个查询上运行EXPLAIN PLAN。

带有列的第一个查询不包含任何键列，因此我猜测它必须进行TABLE SCAN。

带有“SELECT *”的第二个查询包括主键，因此它可以使用索引。

Answer 2

最后应用范围过滤器，因此问题在于查询优化器选择在一种情况下首先连接较大的表，而在另一种情况下首先连接较小的表。也许对优化器有更多了解的人可以告诉我们为什么它们以不同的顺序加入表中。

我认为这里的真正目标应该是尝试让JOIN使用索引，因此连接的顺序无关紧要。

Answer 3

我会尝试在locId，count，avg上放置一个复合索引，看看是否会提高速度。

MySQL选择比select *更慢的特定cols

3 个答案: