Stripping Comments so Query Cache Works in MariaDB and XtraDB

I recently noticed both MariaDB and XtraDB (not MySQL yet) have a (newer) variable query_cache_strip_comments.

This variable is great for those who want to append comments to various queries, but still want the query cache to be able to serve such queries. Unfortunately, with MySQL, this is not currently possible.

In the past, I wrote a post on using MySQL Proxy which described a technique of monitoring queries through the proxy by appending IP addresses to the queries so one could track where they originated from. However, one pitfall to that was the MySQL query cache *does not* ignore the comment and treats them all as different queries (see the user comments for further discussion). (I did subsequently enhance that functionality implementing the SHOW PROXY PROCESSLIST command (often used in the Proxy Admin module), in large part because of this limitation.)

To enable it (in MariaDB 5.3+ and XtraDB), just add query_cache_strip_comments under the [mysqld] section in your my.cnf file and restart mysqld.

Alternatively, you can also set it dynamically:

mysql> set @@global.query_cache_strip_comments=1;
Query OK, 0 rows affected (0.04 sec)

mysql> show global variables like 'query_cache_strip_comments';
+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| query_cache_strip_comments | ON    |
+----------------------------+-------+

mysql> select version();
+---------------+
| version()     |
+---------------+
| 5.3.3-MariaDB |
+---------------+

Fwiw, from examining the source code, both implementations seemed to differ, but the end result is the same, and it’s a welcome addition, if you ask me.