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From: Kevin Grittner <Kevin.Grittner@wicourts.gov>
To: Benedict Holland <benedict.m.holland@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Update blocking a select count(*)?
Date: Fri, 15 Jun 2012 15:38:39 -0500
Message-ID: <4FDB56FF0200002500048510@gw.wicourts.gov> (raw)
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	<CAD+mzoykMCtGaAKN9jOyH=nDF1E=EORcs4DSAbbKwvt4jJEXsQ@mail.gmail.com>
	<4FDB40B702000025000484EE@gw.wicourts.gov>
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	<4FDB4DF602000025000484FE@gw.wicourts.gov>
	<CAD+mzoyBbX6z9erCNdp2gSP_xBLJOZQFiN7F-BJCS+-O1Sqbmg@mail.gmail.com>

Benedict Holland <benedict.m.holland@gmail.com> wrote:
 
> I ran the scripts on the page and both returned empty (though I
> have queries running and currently nothing blocks). I don't know
> what they should have been.
 
It only shows information on blocking, so the list should be empty
when there is none.  :-)  If it works as intended, it would have
shown the chain of blocking, from the update to the alter to the
select.
 
> The output was from PgAdmin3 which is a UI for postgres. I assume
> that they get this queried information from something inside of
> postgres as I can't imagine the query tool doing something other
> than querying the database for specs.
 
They are probably doing something internally which is somewhat
similar to the recursive query on that page.  It sounds like when
there is a chain or tree of blocking, they show the process at the
front of the parade, rather than the immediate blocker.  I can't say
that's right or wrong, but it should be documented so that people
can understand what they're looking at.  Even better would be to
make a nice graphical tree of the blocking, but that would be
getting pretty fancy.  :-)
 
-Kevin



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