Comments on: MySQL – EXPLAIN Yourself http://blog.theplanet.com/2008/11/13/mysql-explain-yourself/ Welcome To The Planet's Weblog! Sat, 14 Nov 2009 22:33:20 -0600 http://wordpress.org/?v=2.8.5 hourly 1 By: Matthew http://blog.theplanet.com/2008/11/13/mysql-explain-yourself/comment-page-1/#comment-7383 Matthew Thu, 11 Jun 2009 13:49:01 +0000 http://blog.theplanet.com/?p=1100#comment-7383 AaronA: Yes, the improvement in performance is noticed everywhere. I've seen queries that originally took several seconds go down to sub-second once a couple indexes where added. The indexes, usually kept in memory, keep MySQL from having to access the disk which we all know is the slowest piece in a server. Chris: I agree with you. If I really just wanted a raw count, I would have done a COUNT(*). However, that wasn't the point of the article and that was the super-simple query I thought of to illustrate my point of the indexes. Also agreed, that if you give a dumb query it can help "somewhat." I hope you'll agree that an optimized "dumb query" is still better than a "dumb query" that does full-table scans or uses a disk-temp-table. AaronA:
Yes, the improvement in performance is noticed everywhere. I’ve seen queries that originally took several seconds go down to sub-second once a couple indexes where added. The indexes, usually kept in memory, keep MySQL from having to access the disk which we all know is the slowest piece in a server.

Chris:
I agree with you. If I really just wanted a raw count, I would have done a COUNT(*). However, that wasn’t the point of the article and that was the super-simple query I thought of to illustrate my point of the indexes.

Also agreed, that if you give a dumb query it can help “somewhat.” I hope you’ll agree that an optimized “dumb query” is still better than a “dumb query” that does full-table scans or uses a disk-temp-table.

]]> By: Chris http://blog.theplanet.com/2008/11/13/mysql-explain-yourself/comment-page-1/#comment-7381 Chris Wed, 10 Jun 2009 22:13:17 +0000 http://blog.theplanet.com/?p=1100#comment-7381 I get that this is a post about using EXPLAIN, but EXPLAIN doesn't show you that the better query would be "SELECT count(*) FROM user_activity WHERE activity='Login'". Your code is cleaner and you don't waste all that network bandwidth moving useless bytes from the database to the application. ALSO, selecting "*" from that table means that the query must load all the table data... if you only selected the 'activity' column, you'd find that the index itself can fulfill the entire query: the table data itself doesn't have to be consulted. EXPLAIN can only help optimize what MySQL does with the query you give to it. If you're giving it a dumb query, it can't really help you, now can it? I get that this is a post about using EXPLAIN, but EXPLAIN doesn’t show you that the better query would be “SELECT count(*) FROM user_activity WHERE activity=’Login’”.

Your code is cleaner and you don’t waste all that network bandwidth moving useless bytes from the database to the application.

ALSO, selecting “*” from that table means that the query must load all the table data… if you only selected the ‘activity’ column, you’d find that the index itself can fulfill the entire query: the table data itself doesn’t have to be consulted.

EXPLAIN can only help optimize what MySQL does with the query you give to it. If you’re giving it a dumb query, it can’t really help you, now can it?

]]> By: Steven http://blog.theplanet.com/2008/11/13/mysql-explain-yourself/comment-page-1/#comment-7153 Steven Thu, 04 Dec 2008 18:56:34 +0000 http://blog.theplanet.com/?p=1100#comment-7153 Nice post. I wasn't aware of the EXPLAIN statement, or (and I'm ashamed to admit this) the benefit of adding non-primary indexes. I'll be sure to take this into consideration for my future projects. Thanks! Nice post. I wasn’t aware of the EXPLAIN statement, or (and I’m ashamed to admit this) the benefit of adding non-primary indexes. I’ll be sure to take this into consideration for my future projects. Thanks!

]]> By: JeremiahX.com » Blog Archive » MySQL Explain Yourself! http://blog.theplanet.com/2008/11/13/mysql-explain-yourself/comment-page-1/#comment-7152 JeremiahX.com » Blog Archive » MySQL Explain Yourself! Thu, 04 Dec 2008 16:56:12 +0000 http://blog.theplanet.com/?p=1100#comment-7152 [...] http://blog.theplanet.com/2008/11/13/mysql-explain-yourself/ Read More Post a Comment [...] [...] http://blog.theplanet.com/2008/11/13/mysql-explain-yourself/ Read More Post a Comment [...]

]]> By: AaronA http://blog.theplanet.com/2008/11/13/mysql-explain-yourself/comment-page-1/#comment-7146 AaronA Tue, 18 Nov 2008 16:27:16 +0000 http://blog.theplanet.com/?p=1100#comment-7146 i had no idea you could run such a simple command to track down such a glaring inefficiency. for a little more context, is the improvement in performance very noticeable on the user side? i had no idea you could run such a simple command to track down such a glaring inefficiency. for a little more context, is the improvement in performance very noticeable on the user side?

]]> By: Kevin Hazard, Web Hosting Evangelist http://blog.theplanet.com/2008/11/13/mysql-explain-yourself/comment-page-1/#comment-7145 Kevin Hazard, Web Hosting Evangelist Tue, 18 Nov 2008 16:24:11 +0000 http://blog.theplanet.com/?p=1100#comment-7145 Awesome post, Matthew! Awesome post, Matthew!

]]> By: GFMorris.com » links for 2008-11-15 http://blog.theplanet.com/2008/11/13/mysql-explain-yourself/comment-page-1/#comment-7143 GFMorris.com » links for 2008-11-15 Sun, 16 Nov 2008 02:36:06 +0000 http://blog.theplanet.com/?p=1100#comment-7143 [...] The Planet Blog » Blog Archive » MySQL - EXPLAIN Yourself (tags: MySQL EXPLAIN) [...] [...] The Planet Blog » Blog Archive » MySQL – EXPLAIN Yourself (tags: MySQL EXPLAIN) [...]

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