Comments on: assert_efficient_sql http://enfranchisedmind.com/blog/posts/assert_efficient_sql/ programming, politics, & other religious issues Mon, 15 Mar 2010 00:31:40 +0000 hourly 1 By: Robert Fischer http://enfranchisedmind.com/blog/posts/assert_efficient_sql/#comment-32308 Robert Fischer Mon, 14 Jan 2008 15:41:27 +0000 http://enfranchisedmind.com/blog/2008/01/14/assert_efficient_sql/#comment-32308 You probably don't want to set the knob too low. It really is a lot faster to just do table scans than to use an index and followed by table look-ups in many cases. The particular count of rows depends on a lot of different factors (whether you have fixed-width or variable-width fields, whether you have nullable fields, the number of columns, various buffer sizes, etc., etc.), but my experience from performance tuning MySQL has generally shown that it's a lot higher than I'd otherwise guess. You probably don’t want to set the knob too low. It really is a lot faster to just do table scans than to use an index and followed by table look-ups in many cases. The particular count of rows depends on a lot of different factors (whether you have fixed-width or variable-width fields, whether you have nullable fields, the number of columns, various buffer sizes, etc., etc.), but my experience from performance tuning MySQL has generally shown that it’s a lot higher than I’d otherwise guess.

]]> By: Phlip http://enfranchisedmind.com/blog/posts/assert_efficient_sql/#comment-32307 Phlip Mon, 14 Jan 2008 15:09:59 +0000 http://enfranchisedmind.com/blog/2008/01/14/assert_efficient_sql/#comment-32307 Thanks for the tips - I'll look at implementing them. About "an excessive amount of queries", the general goal is you put the assertion around anything. I have put it around functional test post:action calls, for example. So the assertion should not guess how many different queries you should run in your production code, or how many different phases each one should run. About "punt to full table scans on smaller tables", I will ask the MySQL internals mailing list if I can set their knob very low there! Thanks for the tips – I’ll look at implementing them.

About “an excessive amount of queries”, the general goal is you put the assertion around anything. I have put it around functional test post:action calls, for example. So the assertion should not guess how many different queries you should run in your production code, or how many different phases each one should run.

About “punt to full table scans on smaller tables”, I will ask the MySQL internals mailing list if I can set their knob very low there!

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