Lists: | pgsql-sql |
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From: | teknokrat <teknokrat(at)yahoo(dot)com> |
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To: | pgsql-sql(at)postgresql(dot)org |
Subject: | does postgresql execute unions in parallel? |
Date: | 2003-09-25 17:04:23 |
Message-ID: | bkv76m$h4f$1@news.hub.org |
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Lists: | pgsql-sql |
If I have several selects joined with unions does postgresql execute the
concurrently or not?
thanks
From: | Gaetano Mendola <mendola(at)bigfoot(dot)com> |
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To: | "pgsql-sql(at)postgresql(dot)org" <pgsql-sql(at)postgresql(dot)org> |
Cc: | teknokrat(at)yahoo(dot)com |
Subject: | Re: does postgresql execute unions in parallel? |
Date: | 2003-09-26 19:58:59 |
Message-ID: | 3F749A83.30001@bigfoot.com |
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teknokrat wrote:
> If I have several selects joined with unions does postgresql execute the
> concurrently or not?
nope.
Regards
Gaetan Mendola
From: | Christopher Browne <cbbrowne(at)acm(dot)org> |
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To: | pgsql-sql(at)postgresql(dot)org |
Subject: | Re: does postgresql execute unions in parallel? |
Date: | 2003-09-26 20:28:23 |
Message-ID: | 604qyz2t20.fsf@dev6.int.libertyrms.info |
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mendola(at)bigfoot(dot)com (Gaetano Mendola) writes:
> teknokrat wrote:
>> If I have several selects joined with unions does postgresql
>> execute the concurrently or not?
>
> nope.
I was talking with Jan about that very idea yesterday; this would seem
to be the place where PostgreSQL might take some (possibly even nearly
magical :-)) benefit from threading.
The usual way that people expect to use threading is for each
connection to have a thread.
If, instead, every _join_ had a thread, that would allow producers of
data to look for their data quasi-independently, passing result sets
upwards towards the return set to whatever thread was waiting to
consume the data.
This would allow one complex query to take over a whole horde of
processors :-).
The "magic" part would be if the system decided, "The SEQ SCAN on the
table I'm looking at is a big one; let's split it into 4 chunks, doing
a virtual UNION ALL, and thereby filter bits of it in parallel on 4
CPUs." That would provide many of the benefits Informix claimed from
"fragmentation" without having to fragment the table :-).
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From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
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To: | teknokrat(at)yahoo(dot)com |
Cc: | pgsql-sql(at)postgresql(dot)org |
Subject: | Re: does postgresql execute unions in parallel? |
Date: | 2003-09-29 17:54:48 |
Message-ID: | 200309291754.h8THsmK08178@candle.pha.pa.us |
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teknokrat wrote:
> If I have several selects joined with unions does postgresql execute the
> concurrently or not?
No.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
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