I should've added to the previous comment - this will compare properly to postgresql. comparing myisam tables to postgresql won't tell you anything - they are completely different.
the innodb engine on the other hand supports row level locking which means count(*) type queries can't use the table metadata (like a myisam table can).
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Try using the mysql 'innodb' engine instead of myisam.. you'll see a performance difference (see mysql.com for details on why they are different).
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I should've added to the previous comment - this will compare properly to postgresql. comparing myisam tables to postgresql won't tell you anything - they are completely different.
the innodb engine on the other hand supports row level locking which means count(*) type queries can't use the table metadata (like a myisam table can).