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From:Dan Nelson Date:May 29 2009 9:16pm
Subject:Re: Why can't I kill the query cache?
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In the last episode (May 29), Gerald L. Clark said:
> Little, Timothy wrote:
> > Also titled, I want this to run slow ALL the time...
> > 
> > I have a group of dreadful queries that I have to optimize.  
> > 
> > Some take 20-30 seconds each -- the first time that I run them.  But
> > then they never seem to take that long after the first time (taking less
> > than a second then).  If I change the "keywords" searched for in the
> > where clauses, then they take a long time again...  so it's the
> > query-cache or something just like it.
> > 
> > BUT, I am doing this each time :
> > flush tables;
> > reset query cache;
> > set global query_cache_size=0;
> > SELECT   SQL_NO_CACHE DISTINCT ca.conceptid AS headingid,
> > 
> > And still it's not avoiding the cache.
> > 
> > Is there a cache I'm missing?
> > 
> > Tim...
> > 
> > 
> Disk cache, but I don't know how to clear it.

Create a file 2x the size of your RAM (for a 2gb system, dd if=/dev/zero
of=bigfile bs=1024k count=4096), then dd it to /dev/null (dd if=bigfile
of=/dev/null bs=1024k).  That should flush your OS cache.  The guaranteed
way would be to dismount then remount your filesystem, but that could be
difficult depending on how many other processes are using it..

-- 
	Dan Nelson
	dnelson@stripped
Thread
contributing to mysql ..mugisha moses27 May
  • Re: contributing to mysql ..Mattia Merzi27 May
    • RE: contributing to mysql ..Martin Gainty27 May
    • Why can't I kill the query cache?Timothy Little29 May
      • Re: Why can't I kill the query cache?Gerald L. Clark29 May
        • Re: Why can't I kill the query cache?Dan Nelson29 May
          • Re: Why can't I kill the query cache?Eric Bergen29 May
            • Re: Why can't I kill the query cache?Baron Schwartz30 May