Re: 5.1 to 5.5 upgrade causes significant write slowdown (MyISAM + indexes)

[Ben Wallach]

The I/O is definitely cranking during the job writes.
The memory is not though. There is 16GB of RAM. MySQL is really the only thing on the boxes. Top shows ~3GB not even used (before we even look at buffers/cache)..

I was curious as to whether increasing the memory allocation (in my.cnf) had anything to do with this, but if anything it should help. Right? We have 16GB installed. 8GB for INNODB and 4GB for MyISAM in my.cnf. That still leavs 4GB for OS (plenty I would think).

On the topic of migrating to INNODB, we are not prepared to do that yet (Over 107 MYISAM tables and not certain as to consequences). However, just as a test, created the same table as defined above but with innodb storage engine. The insert job was on track to complete in ~2.5 hours! Stopped it a few minutes into it. This is the same behavior I experienced 6 years ago on an older version of MySQL...and thus decided to stay away from INNODB as we do very heavy nightly writing... Why would running ~200k insert statements into an INNODB table take that long??