Message-ID: <25525.203.121.164.162.1158315505.squirrel@webmail.xs4all.nl>
In-Reply-To: <450A6A87.2030808@microbizz.nl>
References: <450A6A87.2030808@microbizz.nl>
Date: Fri, 15 Sep 2006 17:18:25 +0700 (ICT)
Subject: Re: Progress of asynchronous queries
From: "Jeroen T. Vermeulen" <jtv@xs4all.nl>
To: "Adriaan van Os" <postgres@microbizz.nl>
Cc: pgsql-interfaces@postgresql.org
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On Fri, September 15, 2006 15:55, Adriaan van Os wrote:
> I couldn't find anything in the libpq interfaces that identifies the
> current progress of an
> asynchronous query as a percentage of the estimated total query time. So,
> unless I missed
> something, I would like to file this as a feature request.
>
> The idea behind this, of course, is to show a progress bar in the user
> interface of the client
> application as soon as the query takes longer than say 1 second.

One way to do this would be to use a cursor, and only receive batches of
(say) a hundred or a thousand rows at a time.  In that case you might not
even want to bother with asynchronous execution at all.

It may take some extra work for your program to handle its data in chunks.
 Then again, for many programs it's not necessary to hold all of a result
set in memory at the same time.  In that case you may see reduced memory
usage if you request one chunk of data through a cursor, process it, then
request the next batch.

Doing that will take longer overall but give you faster initial response
time.  If you want to keep the overall time low, and you do a lot of
processing per batch, you may still want to request your batches
asynchronously just so your program can process one batch of data while
the server is retrieving the next.


Jeroen