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Re: [DOCS] Partition: use triggers instead of rules

From: NikhilS <nikkhils(at)gmail(dot)com>
To: "Gregory Stark" <stark(at)enterprisedb(dot)com>
Cc: "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "Michael Paesold" <mpaesold(at)gmx(dot)at>, "David Fetter" <david(at)fetter(dot)org>, "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>, "PostgreSQL Docs" <pgsql-docs(at)postgresql(dot)org>, "PostgreSQL Patches" <pgsql-patches(at)postgresql(dot)org>
Subject: Re: [DOCS] Partition: use triggers instead of rules
Date: 2007-11-30 07:04:05
Message-ID: (view raw or whole thread)
Lists: pgsql-docspgsql-patches

On Nov 30, 2007 1:52 AM, Gregory Stark <stark(at)enterprisedb(dot)com> wrote:

> "Joshua D. Drake" <jd(at)commandprompt(dot)com> writes:
> > If you have lots of data it doesn't mean you are modifying lots of
> > data.
> It sure can. How do you modify lots of data if you *don't* have lots data
> in
> the first place? Certainly it doesn't mean you necessarily are, some
> databases
> are OLTP which do no large updates. But data warehouses with oodles of
> data
> also often have to do large updates or deletions.
> > I don't think anyone here (good lord I hope not) would say that firing
> > a trigger over 500k rows is fast. Instead you should likely just work
> the data
> > outside the partition and then move it directly into the target
> > partition.
> Well you don't even have to do that. You can issue the updates directly
> against the partitions. In fact, that's precisely what the rules
> effectively
> do... Rules rewrite the query to be a query directly against the
> partitions.
> Come to think of it I think there actually is a correct way to use rules
> which
> wouldn't suffer from the problems that have come up. Instead of putting a
> WHERE clause on the rule just expand deletes and updates to expand to
> deletes
> and updates against *all* partitions. Then let constraint_exclusion kick
> in to
> narrow down which partitions should actually receive the updates and
> deletes.
> I think triggers are the only solution for insert though.

Another reason to go along with triggers is that "COPY" honors triggers, but
does not honor rules. While trying to do bulk inserts into a parent of
partitioned tables where rules are being employed, the COPY operation will
not be so straightforward.


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