From: Johan De Meersman
Date: March 31 2011 4:06pm
Subject: Re: A common request
List-Archive: http://lists.mysql.com/mysql/224735
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----- Original Message -----
> From: "Gregory Magarshak" <greg@stripped>
> I am guessing that the MySQL indexes map indexed fields (fb_uid) to the
> primary key (id) so I wouldn't have to touch the disk. Am I right
> about that?

Correct for InnoDB, but MyISAM maps every index straight onto records. That's why secondary indices are slightly more performant on MyISAM tables - InnoDB needs to do the extra primary key lookup - which it of course is bloody good at :-)


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