Know your my.cnf groups, part II
Jan 27, 2010 / By Sheeri Cabral
Ronald Bradford‘s recent warning to be sure to know your my.cnf sections reminded me of a similar issue that I ran into last summer, where putting the “group” option in both the [mysqld_safe] and [mysqld] directives resulted in a mostly silent problem.
I started noticing this in MySQL 5.1 and it affected both the official MySQL binary and the Percona binary. In trying to be conscientious, I had the following set:
However, when the MySQL server started up, the error log showed
[Warning] option 'group_concat_max_len': unsigned value 0 adjusted to 4
This was obviously a problem, but I only started noticing it during MySQL restarts, which was mostly during upgrades to MySQL 5.1. I tracked it down and realized that when I removed the “group” option from the [mysqld] directive, the warning did not come up.
The problem is that [safe_mysqld] sees “group” as the “group” option, but [mysqld] does not know about the “group” option. The MySQL server allows the shortest unique identifier of an option to *be* that option. Thus, “group” is an acceptable abbreviation for “group_concat_max_len”.
So mysqld was taking:
and translating it to:
but “mysql” is a string, not a number, so MySQL tried to be helpful by converting to a number….so it was as if I stated:
I filed a bug for this back in June:
http://bugs.mysql.com/bug.php?id=45379. The response was “If 3 different people ask about removing this feature reclassifying report to feature request with new synopsis.”
So, a second moral: make a bug report if you want things to get changed, and if you see a bug report for a problem you’re encountering, make sure to add your voice so that MySQL understands that an issue is indeed serious.
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