[英]Optimizing query in the MySQL slow-query log
设置数据库是为了使我们拥有一个credentials
表,其中包含多种不同类型的凭证(登录等)。 还有一个credential_pairs
表将这些类型中的某些类型关联在一起(例如,用户可能具有密码和安全令牌)。
为了查看对是否匹配,有以下查询:
SELECT DISTINCT cp.credential_id FROM credential_pairs AS cp
INNER JOIN credentials AS c1 ON (cp.primary_credential_id = c1.credential_id)
INNER JOIN credentials AS c2 ON (cp.secondary_credential_id = c2.credential_id)
WHERE c1.data = AES_ENCRYPT('Some Value 1', 'encryption key')
AND c2.data = AES_ENCRYPT('Some Value 2', 'encryption key');
该查询可以正常工作,并为我们提供所需的确切信息。 但是,它一直在缓慢的查询日志中显示(可能由于缺少索引?)。 当我要求MySQL“解释”查询时,它给了我:
+----+-------------+-------+------+--------------------------------------------------------+---------------------+---------+-------+-------+--------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+--------------------------------------------------------+---------------------+---------+-------+-------+--------------------------------+
| 1 | SIMPLE | c1 | ref | credential_id_UNIQUE,credential_id,ix_credentials_data | ix_credentials_data | 22 | const | 1 | Using where; Using temporary |
| 1 | SIMPLE | c2 | ref | credential_id_UNIQUE,credential_id,ix_credentials_data | ix_credentials_data | 22 | const | 1 | Using where |
| 1 | SIMPLE | cp | ALL | NULL | NULL | NULL | NULL | 69197 | Using where; Using join buffer |
+----+-------------+-------+------+--------------------------------------------------------+---------------------+---------+-------+-------+--------------------------------+
我觉得最后一个条目(显示69197行)可能是问题所在,但我是DBA的FAR ...帮助?
凭证表:
CREATE TABLE `credentials` (
`hidden_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`credential_id` varchar(255) NOT NULL,
`data` blob NOT NULL,
`credential_status` varchar(100) NOT NULL,
`insert_date` datetime NOT NULL,
`insert_user` int(10) unsigned NOT NULL,
`update_date` datetime DEFAULT NULL,
`update_user` int(10) unsigned DEFAULT NULL,
`delete_date` datetime DEFAULT NULL,
`delete_user` int(10) unsigned DEFAULT NULL,
`is_deleted` tinyint(1) NOT NULL DEFAULT '0',
PRIMARY KEY (`hidden_id`,`credential_id`),
UNIQUE KEY `credential_id_UNIQUE` (`credential_id`),
KEY `credential_id` (`credential_id`),
KEY `data` (`data`(10)),
KEY `credential_status` (`credential_status`(10))
) ENGINE=InnoDB AUTO_INCREMENT=1572 DEFAULT CHARSET=utf8;
credential_pairs表:
CREATE TABLE `credential_pairs` (
`hidden_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`credential_id` varchar(255) NOT NULL,
`primary_credential_id` varchar(255) NOT NULL,
`secondary_credential_id` varchar(255) NOT NULL,
`is_deleted` tinyint(1) DEFAULT NULL,
PRIMARY KEY (`hidden_id`,`credential_id`),
KEY `primary_credential_id` (`primary_credential_id`(10)),
KEY `secondary_credential_id` (`secondary_credential_id`(10))
) ENGINE=InnoDB AUTO_INCREMENT=500 DEFAULT CHARSET=latin1;
凭证索引:
+-------------+------------+----------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------------+------------+----------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+
| credentials | 0 | PRIMARY | 1 | hidden_id | A | 186235 | NULL | NULL | | BTREE | |
| credentials | 0 | PRIMARY | 2 | credential_id | A | 186235 | NULL | NULL | | BTREE | |
| credentials | 0 | credential_id_UNIQUE | 1 | credential_id | A | 186235 | NULL | NULL | | BTREE | |
| credentials | 1 | credential_id | 1 | credential_id | A | 186235 | NULL | NULL | | BTREE | |
| credentials | 1 | ix_credentials_data | 1 | data | A | 186235 | 20 | NULL | | BTREE | |
+-------------+------------+----------------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+
credential_pair索引:
+------------------+------------+---------------------------------------------+--------------+-------------------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+------------------+------------+---------------------------------------------+--------------+-------------------------+-----------+-------------+----------+--------+------+------------+---------+
| credential_pairs | 0 | PRIMARY | 1 | hidden_id | A | 69224 | NULL | NULL | | BTREE | |
| credential_pairs | 0 | PRIMARY | 2 | credential_id | A | 69224 | NULL | NULL | | BTREE | |
| credential_pairs | 1 | ix_credential_pairs_credential_id | 1 | credential_id | A | 69224 | 36 | NULL | | BTREE | |
| credential_pairs | 1 | ix_credential_pairs_primary_credential_id | 1 | primary_credential_id | A | 69224 | 36 | NULL | | BTREE | |
| credential_pairs | 1 | ix_credential_pairs_secondary_credential_id | 1 | secondary_credential_id | A | 69224 | 36 | NULL | | BTREE | |
+------------------+------------+---------------------------------------------+--------------+-------------------------+-----------+-------------+----------+--------+------+------------+---------+
更新说明:
AFAICT:DISTINCT是多余的……真的不需要它,所以我删除了它。 为了遵循Fabrizio的建议,在credential_pairs查找中找到位置,然后将语句更改为:
SELECT credential_id
FROM credential_pairs cp
WHERE cp.primary_credential_id = (SELECT credential_id FROM credentials WHERE data = AES_ENCRYPT('value 1','enc_key')) AND
cp.secondary_credential_id = (SELECT credential_id FROM credentials WHERE data = AES_ENCRYPT('value 2','enc_key'))
没事了。 该语句花了很长时间,并且解释看起来几乎相同。 因此,我使用以下命令向主列和辅助列添加了索引:
ALTER TABLE credential_pairs ADD INDEX `idx_credential_pairs__primary_and_secondary`(`primary_credential_id`, `secondary_credential_id`);
没事了。
+----+-------------+-------------+-------+---------------------+---------------------------------------------+---------+------+-------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------------+-------+---------------------+---------------------------------------------+---------+------+-------+--------------------------+
| 1 | PRIMARY | cp | index | NULL | idx_credential_pairs__primary_and_secondary | 514 | NULL | 69217 | Using where; Using index |
| 3 | SUBQUERY | credentials | ref | ix_credentials_data | ix_credentials_data | 22 | | 1 | Using where |
| 2 | SUBQUERY | credentials | ref | ix_credentials_data | ix_credentials_data | 22 | | 1 | Using where |
+----+-------------+-------------+-------+---------------------+---------------------------------------------+---------+------+-------+--------------------------+
它说它正在使用索引,但看起来仍然像是表扫描。 因此,我添加了一个联合键(按照下面的评论):
ALTER TABLE credential_pairs ADD KEY (primary_credential_id, secondary_credential_id);
并且...与索引的结果相同(这些功能是否相同?)。
DISTINCT是生成“使用临时”的原因,您通常希望尽可能避免使用
另外,由于您没有针对它的任何条件,因此您正在扫描整个credential_pair
表,因此不使用任何索引,并且在应用WHERE之前将返回整个表
希望有道理
编辑/添加
尝试从另一个表开始,如果我理解正确,那么您具有表A,表B和表AB,并且您正在从AB开始选择,请尝试从A开始
我尚未对此进行测试,但是您可以尝试:
SELECT cp.credential_id
FROM credentials AS c1
LEFT JOIN credential_pairs AS cp ON (c1.credential_id = cp.primary_credential_id)
LEFT JOIN credentials AS c2 ON (cp.secondary_credential_id = c2.credential_id)
WHERE
c1.data = AES_ENCRYPT('Some Value 1', 'encryption key')
AND c2.data = AES_ENCRYPT('Some Value 2', 'encryption key');
过去,我通过移动选择表来获得好运
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