Have a look at Mysql gotchas...
http://sql-info.de/mysql/database-definition.html#2_4
>
> So here's another little gem about our friends from Uppsala: If you create a
> table with InnoDB storage and your server does not have InnoDB configured, it
> falls back to MyISAM without telling you.
>
> As it turns out, the test done with PostgreSQL vs. real InnoDB results in just
> about identical timings (90 min). The test done using PostgreSQL with fsync
> off vs. MyISAM also results in about identical timings (3 min). So that
> looks much better, although the update performance of PostgreSQL is still a
> lot worse.
>