Much activity for general_log.CSM even though general log is disabled

[David Raimosson]

Hi!

Earlier this year I enabled the general log for a few minutes on our production server. After disabling it we've seen something strange in our db stats, also on replicated instances.

This query:

-- Top I/O by File by Time
SELECT *
FROM sys.`x$io_global_by_file_by_latency`
WHERE
file NOT LIKE '/var/lib/mysql/ib_logfile%'
AND file NOT LIKE '/var/lib/mysql/mh-dbc01-bin.%'
ORDER BY
total_latency DESC
LIMIT 100;

gives:

# file, total total_latency count_read read_latency count_write write_latency count_misc misc_latency
/var/lib/mysql/ibdata1 698982 56550758541970 0 0 620215 41225163395185 78767 15325595146785
/var/lib/mysql/... 1215770 21162224023325 1736 1243221790965 1197203 17609754324470 16831 2309247907890
/var/lib/mysql/mysql/general_log.CSM 45680 17171608207985 5710 66556573160 5710 122909736180 34260 16982141898645
...

So, one can see that the general_log.CSM is on third place in total latency source. Even though the general log isn't enabled. It has been like this for months.

SELECT @@general_log;
> 0

In /var/lib/mysql/mysql I find:

-rw-rw---- 1 mysql mysql 35 Apr 20 08:34 general_log.CSM
-rw-rw---- 1 mysql mysql 0 Mar 8 2016 general_log.CSV
-rw-rw---- 1 mysql mysql 8776 Mar 8 2016 general_log.frm

This should only happen when the general log is enabled and the log_output is set to table (or perhaps a combination of file and table), but it has always been set to file only.

SELECT @@log_output;
> FILE

Our MySQL version (I know, it's Percona, that might be the problem):
SELECT @@version;
> 5.6.26-74.0-56-log

Has anyone ever heard about this behavior? Any help appreciated.

Best regards

David