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.
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TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match
