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From: Andrew Chernow <ac@esilo.com>
To: Alvaro Herrera <alvherre@commandprompt.com>
Cc: Pavel Golub <pavel@gf.microolap.com>
Cc: Pavel Golub <pavel@microolap.com>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Cc: pgsql-interfaces <pgsql-interfaces@postgresql.org>
Subject: Re: PQdeleteTuple function in libpq
Date: Thu, 02 Jun 2011 12:12:16 -0400
Message-ID: <4DE7B660.8040704@esilo.com> (raw)
In-Reply-To: <1307026778-sup-415@alvh.no-ip.org>
References: <147534417.20110601184310@gf.microolap.com>
	<4DE6A5B7.2070700@esilo.com>
	<707574086.20110602112826@gf.microolap.com>
	<4DE79A58.4010608@esilo.com>
	<1307026778-sup-415@alvh.no-ip.org>

On 6/2/2011 11:02 AM, Alvaro Herrera wrote:
> Excerpts from Andrew Chernow's message of jue jun 02 10:12:40 -0400 2011:
>
>>> Andrew, why we have PQmakeEmptyPGresult, PQcopyResult,
>>> PQsetResultAttrs, PQsetvalue and PQresultAlloc in this case? Of course
>>> there's no big deal with their absence but let's be consistent.
>>
>> I'm not entirely sure what you are trying to do, but can't you use
>> PQmakeEmptyPGresult, PQsetResultAttrs and PQsetvalue to construct a
>> result that excludes the tuples you don't want followed by a
>> PQclear(initial_result)?
>
> Seems pretty wasteful if you want to delete a single tuple from a large
> result.  I think if you desired to compact the result to free some
> memory after deleting a large fraction of the tuples in the result it
> could be useful to do that, otherwise just live with the unused holes in
> the storage area as suggested by Pavel.
>

Another solution is to manually cursor through the set (like grab 1000 
tuples at a time) and copy the set to your own structure.  That way, the 
temporary double memory to perform the copy is not as big of a hit.  By 
using your own structure, you can organize the memory in a fashion that 
is optimized for your requirement.

-- 
Andrew Chernow
eSilo, LLC
global backup
http://www.esilo.com/

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