Question

我想知道我是否可以更好地优化它，也许有人在努力。

首先我有桌子：

CREATE TABLE `site_url` (
    `id` BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT,
    `url_hash` CHAR(32) NULL DEFAULT NULL,
    `url` VARCHAR(2048) NULL DEFAULT NULL,
    PRIMARY KEY (`id`),
    INDEX `url_hash` (`url_hash`)
)
ENGINE=InnoDB;

我在哪里存储网站URI（域名在不同的表中，但出于这个问题的目的，id并不重要 - 我希望）

url_hash是根据url

计算的MD5

似乎所有字段的长度都很长，索引应该是正确的，但其中有一些数据，我正在寻找更多优化。

标准查询如下所示：

select id from site_url where site_url.url_hash = MD5('something - often calculated in application rather than in mysql') and site_url.url = 'something - often calculated in application rather than in mysql'

描述给出：

+----+-------------+----------+------+---------------+----------+---------+-------+------+------------------------------------+
| id | select_type |  table   | type | possible_keys |   key    | key_len |  ref  | rows |               Extra                |
+----+-------------+----------+------+---------------+----------+---------+-------+------+------------------------------------+
|  1 | SIMPLE      | site_url | ref  | url_hash      | url_hash |      97 | const |    1 | Using index condition; Using where |
+----+-------------+----------+------+---------------+----------+---------+-------+------+------------------------------------+

但我想知道我是否可以帮助mysql进行搜索。必须通过InnoDB引擎，我才能将密钥添加到url，因为它的长度

我的朋友告诉我将哈希短路到16个字符，并将其写为数字。 BIGINT上的索引是否会快于char(32)上的索引？朋友还建议做MD5并采用它的16个第一个/最后一个字符，但我认为它会产生更多的冲突。

你对此有何看法？

Answer 1

这是您的查询：

select id
from site_url
where site_url.url_hash = MD5('something - often calculated in application rather than in mysql') and
      site_url.url = 'something - often calculated in application rather than in mysql';

此查询的最佳索引位于site_url(url_hash, url, id)。需要注意的是，您可能需要使用前缀，除非您设置了大前缀选项（请参阅innodb_large_prefix）。

Answer 2

如果url_hash是url的md5，为什么用2个键选择？

select id from site_url where site_url.url_hash = MD5('something - often calculated in application rather than in mysql');

实际上你不需要检查site_url.url;

但如果您愿意，可以使用USE INDEX语法选择2个字段：

select id from site_url USE INDEX (url_hash) where site_url.url_hash = MD5('something - often calculated in application rather than in mysql') and site_url.url = 'something - often calculated in application rather than in mysql');

MySQL InnoDB哈希索引优化

2 个答案: