From: | David G Johnston <david(dot)g(dot)johnston(at)gmail(dot)com> |
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To: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Removing duplicate records from a bulk upload (rationale behind selecting a method) |
Date: | 2014-12-12 18:40:27 |
Message-ID: | 1418409627311-5830353.post@n5.nabble.com |
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Lists: | pgsql-general |
John McKown wrote
> I don't
> know, myself, why this would be faster. But I'm not any kind of a
> PostgreSQL expert either.
It is faster because PostgreSQL does not have native parallelism. By using
a%n in a where clause you can start n separate sessions and choose a
different value of n for each one and manually introduce parallelism into
the activity.
Though given this is going to likely be I/O constrained the possible gains
do not scale lineally with the number of sessions - which themselves
effectively max out at the number of cores available to the server.
David J.
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