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Re: Libpq Asynchronous Command Processing

From: Alonso García , Bruno Elier <bealonso(at)indra(dot)es>
To: Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>, Giles Lean<giles(dot)lean(at)pobox(dot)com>
Cc: "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org>
Subject: Re: Libpq Asynchronous Command Processing
Date: 2010-05-31 14:34:31
Message-ID: 63A652C37EE6E04BA5234D623423FF97BBA0648714@MADARRMAILBOX03.indra.es (view raw or flat)
Thread:
Lists: pgsql-general
>> With that analysis, I'd be betting against it being a client problem.
>> (If you wanted, you might confirm that by pointing an old client at
>> the new server.)
>>
>> I'd look into how the data was loaded into the new server and how
>> the database is configured: number of buffers, indexes, and whether
>> analyze has been run or not.
>>
>> It would be strange indeed (possible, but very strange) to find
>> such a slowdown between 7.x and 8.x when the team is preparing
>> to push 9.0 out the door.  Surely it would have been known before;
>> therefore it's a practical certatinty that there is something
>> different about the configuration of your two servers.
>
>... or that the planner is making a bad choice when it made a good one 
>in 7.x . That's far from unheard of; the downside of a stats-based and 
>very complex planner is that sometimes it doesn't make the perfect 
>choice. Even with the same stats, etc, it's far from impossible that 7.x 
>might hit a good plan when 8.x doesn't.
>
>I mention this because the OP really needs to supply EXPLAIN ANALYZE 
>results for the query run via psql (not their custom code) on both their 
>7.x and 8.x servers.

If I perform the query using pgadmin I get the same result in both versions 7.4 and version 8.3. 
In fact I have written two test applications that perform the same query, one using the synchronous command processing (PQexec) an one using the asynchronous Command Processing (PQsendQuery / PQconsumeInput / PQisBusy / PQgetResult) and the results are:
-> synchronous command processing takes less than two seconds to retrieve the result.
-> asynchronous command processing takes more than 120 seconds to retrieve the result.
Both applications are connecting to the same DB so I don't know why I am getting different results. Well I know that PQIsBusy is returning true so I am not executing PQgetResult.
Bruno,

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