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From: andrew@pillette.com
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Subject: Re: Simple select, but takes long time
To: "James DeMichele" <James.DeMichele@redfin.com>
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"James DeMichele" <James.DeMichele@redfin.com> wrote ..

> Then, I have the following index on the table:
 
> "this_index" (status, source_id, <another_column>)

If you have many queries of this type, do

CLUSTER this_index ON tablename;

and retry the SELECT.

MySQL is using some sort of auto-clustering ISAM on the other box mayhaps?

In Postgres you will have to re-CLUSTER periodically if there are INSERTs and UPDATEs.