由于某种原因，ProxySQL 查询缓存并不总是遵守查询规则

Posted 2023-03-28

【中文标题】由于某种原因，ProxySQL 查询缓存并不总是遵守查询规则

【英文标题】：ProxySQL Query Cache doesn't always respect the query rules for some reason

【发布时间】：2021-08-09 02:51:13

【问题描述】：

我使用 ProxySQL (2.0.17) 缓存所有发送到 mysql 的 SELECT 查询。 mysql_query_rules 表如下所示：

+---------+--------+----------+------------+--------+-------------+------------+------------+--------+------------------------------+---------------+----------------------+--------------+---------+-----------------+-----------------------+-----------+--------------------+---------------+-----------+---------+---------+-------+-------------------+----------------+------------------+-----------+--------+-------------+-----------+---------------------+-----+-------+---------+
| rule_id | active | username | schemaname | flagIN | client_addr | proxy_addr | proxy_port | digest | match_digest                 | match_pattern | negate_match_pattern | re_modifiers | flagOUT | replace_pattern | destination_hostgroup | cache_ttl | cache_empty_result | cache_timeout | reconnect | timeout | retries | delay | next_query_flagIN | mirror_flagOUT | mirror_hostgroup | error_msg | OK_msg | sticky_conn | multiplex | gtid_from_hostgroup | log | apply | comment |
+---------+--------+----------+------------+--------+-------------+------------+------------+--------+------------------------------+---------------+----------------------+--------------+---------+-----------------+-----------------------+-----------+--------------------+---------------+-----------+---------+---------+-------+-------------------+----------------+------------------+-----------+--------+-------------+-----------+---------------------+-----+-------+---------+
| 1       | 1      | NULL     | NULL       | 0      | NULL        | NULL       | NULL       | NULL   | ^[(]?SELECT (?!SQL_NO_CACHE) | NULL          | 0                    | CASELESS     | NULL    | NULL            | NULL                  | 300000    | NULL               | NULL          | NULL      | NULL    | NULL    | NULL  | NULL              | NULL           | NULL             | NULL      | NULL   | NULL        | NULL      | NULL                | NULL | 1     | NULL    |
+---------+--------+----------+------------+--------+-------------+------------+------------+--------+------------------------------+---------------+----------------------+--------------+---------+-----------------+-----------------------+-----------+--------------------+---------------+-----------+---------+---------+-------+-------------------+----------------+------------------+-----------+--------+-------------+-----------+---------------------+-----+-------+---------+

一个简单的规则（我也尝试过^SELECT .*）和 300 秒等待缓存的查询被清除。

由于某种原因，每个要缓存的查询的 5% 仍会发送到后端。例如，这是最流行的查询：

+-----------+------------+----------+----------------+--------------------+--------------------------+------------+------------+------------+-------------+----------+----------+-------------------+---------------+
| hostgroup | schemaname | username | client_address | digest             | digest_text              | count_star | first_seen | last_seen  | sum_time    | min_time | max_time | sum_rows_affected | sum_rows_sent |
+-----------+------------+----------+----------------+--------------------+--------------------------+------------+------------+------------+-------------+----------+----------+-------------------+---------------+
| 2         | ------     | ----     |                | 0xFB50749BCFE0DA3C | SELECT * FROM `language` | 12839      | 1621445210 | 1621455115 | 45069293213 | 31321    | 82235606 | 0                 | 56960         |
| -1        | ------     | ----     |                | 0xFB50749BCFE0DA3C | SELECT * FROM `language` | 326243     | 1621445210 | 1621455116 | 0           | 0        | 0        | 0                 | 0             |
+-----------+------------+----------+----------------+--------------------+--------------------------+------------+------------+------------+-------------+----------+----------+-------------------+---------------+

我无法理解这种特殊性。每当我更新stats_mysql_query_digest 时，hostgroup 2（后端）上的count_star 都会递增，而无需等待 300 秒以清除查询。

查询缓存大小设置为 512 Mb。在高峰期，它占用大约 100 Mb。

帮助？..

【问题讨论】：

第二个看起来实际上已经兑现

@nbk 这是相同的查询，具有相同的摘要哈希

是的，我已经看到了，但是看看结尾 sum_rows_sent 0，所以不要发送任何行

@nbk "sum_rows_sent: 发送的总行数。这目前不计算从查询缓存返回的行数" 所以它可以为 0

【参考方案1】：

将mysql-query_cache_size_MB 增加到 5120 MB（这当然是荒谬的）似乎在一定程度上解决了这个问题。该查询的后端请求频率下降了 10 倍（感谢 ProxySQL 的Query Logging，您可以只记录一个查询并对其进行分析）。 cache_ttl 值仍然远未得到尊重，但我想这种解决方法在这一点上总比没有好。