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Re: How long will the query take

From: Bill Moran <wmoran(at)potentialtech(dot)com>
To: "A(dot) Kretschmer" <andreas(dot)kretschmer(at)schollglas(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: How long will the query take
Date: 2010-03-29 16:11:50
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Lists: pgsql-general
In response to "A. Kretschmer" <andreas(dot)kretschmer(at)schollglas(dot)com>:

> In response to John Gage :
> > I ran a query out of pgAdmin, and (as I expected) it took a long  
> > time.  In fact, I did not let it finish.  I stopped it after a little  
> > over an hour.
> > 
> > I'm using 8.4.2 on a Mac with a 2.4GHz processor and 2GB of RAM.
> > 
> > My question is: is there a way to tell how close the query is to being  
> > finished.  It would be a great pity if the query would have finished  
> > in the 10 seconds after I quit it, but I had no way of telling.
> > 
> > As a postscript, I would add that the query was undoubtedly too  
> > ambitious.  I have a reduced set version which I will run shortly.   
> > But I am still curious to know if there is a way to tell how much time  
> > is left.
> No, not really. But you can (and should) run EXPLAIN <your query> to
> obtain the execution plan for that query, und you can show us this plan
> (and the table-definition for all included tables). Maybe someone is able
> to tell you what you can do to speed up your query.

To piggyback on this ... EXPLAIN _is_ the way to know how long your
query will take, but keep in mind it's only an _estimate_.

Given that, in my experience EXPLAIN is pretty accurate 90% of the
time, as long as you analyze frequently enough.

Bill Moran

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