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how could this be?
Posted by: Nathan Cheng
Date: November 20, 2004 01:58PM

I have a query that looks like this:

SELECT ... ORDER BY primary_key_id LIMIT 0,50

The query in this form takes 7 seconds to run on our very powerful production machine. However, in this form


the query takes only 0.09 seconds to run. Even more baffling is this form:

SELECT ... ORDER BY primary_key_id

which takes only 0.3 seconds to run and returns only 150 rows, and this form:


which takes about the same time (0.3 seconds).

How could this be? How could the first form take 7 FULL SECONDS, and the 3rd form be more than 70 times faster!!?? How could it take an otherwise idle dual processor Xeon with a fast RAID and 4GB RAM nearly 7 full seconds to select the first 50 rows from a 150-row result? This makes no sense!

We are running MySQL 4.1.7, though we had this same problem with 4.0.20, and perhaps even with 3.x (but I don't remember that far back).

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Written By
how could this be?
November 20, 2004 01:58PM
November 21, 2004 02:33AM
November 21, 2004 04:04PM
November 21, 2004 04:16PM

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