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Re: BUG #1756: PQexec eats huge amounts of memory

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Denis Vlasenko <vda(at)ilport(dot)com(dot)ua>
Cc: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>,John R Pierce <pierce(at)hogranch(dot)com>, Neil Conway <neilc(at)samurai(dot)com>,pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #1756: PQexec eats huge amounts of memory
Date: 2005-07-13 14:43:41
Message-ID: 1809.1121265821@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-bugs
Denis Vlasenko <vda(at)ilport(dot)com(dot)ua> writes:
> Consider my posts in this thread as user wish to
> * libpq and network protocol to be changed to allow for incremental reads
>   of executed queries and for multiple outstanding result sets,
> 	or, if above thing looks unsurmountable at the moment,
> * libpq-only change as to allow incremental reads of single outstanding
>   result set. Attempt to use pg_numrows, etc, or attempt to execute
>   another query forces libpq to read and store all remaining rows
>   in client's memory (i.e. current behaviour).

This isn't going to happen because it would be a fundamental change in
libpq's behavior and would undoubtedly break a lot of applications.
The reason it cannot be done transparently is that you would lose the
guarantee that a query either succeeds or fails: it would be entirely
possible to return some rows to the application and only later get a
failure.

You can have this behavior today, though, as long as you are willing to
work a little harder at it --- just declare some cursors and then FETCH
in convenient chunks from the cursors.

			regards, tom lane

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Next:From: Denis VlasenkoDate: 2005-07-13 14:56:47
Subject: Re: BUG #1756: PQexec eats huge amounts of memory
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Subject: Re: BUG #1764: newbie

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