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From:Dave Dyer Date:August 27 2011 8:52pm
Subject:a lesson in query writing and (maybe) a bug report
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The "innocuous change" was to add an index for "is_robot" which is true
for 6 out of 20,000 records and null for the rest.

My complaint/question/observation is not how to optimize the query
that went awry, but to be alarmed that a venerable and perfectly 
serviceable query, written years ago and ignored ever since, suddenly
brought the system crashing down after making a seemingly innocuous
change intended to make a marginal improvement on an unrelated query.

I had previously believed that tinkering the schema by adding indexes was a safe activity.
 It's as though I add a shortcut to my regular commute
and caused a massive traffic jam when the entire traffic flow tried to
follow me.
    
(Both tables are "ok" according to analyze table)

Thread
a lesson in query writing and (maybe) a bug reportDave Dyer27 Aug
Re: a lesson in query writing and (maybe) a bug reportJigal van Hemert27 Aug
  • Re: a lesson in query writing and (maybe) a bug reportArthur Fuller27 Aug
    • Re: a lesson in query writing and (maybe) a bug reportshawn wilson28 Aug
      • Re: a lesson in query writing and (maybe) a bug reportJigal van Hemert28 Aug
Re: a lesson in query writing and (maybe) a bug reportMichael Dykman28 Aug