From: Joshua D. Drake <jd@commandprompt.com>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Pg Hackers <pgsql-hackers@postgresql.org>
Subject: Re: Indirect indexes
Date: Tue, 18 Oct 2016 12:41:16 -0700
Message-ID: <2f5e6c38-4103-3def-2d6a-24d6509ed34e@commandprompt.com> (raw)
In-Reply-To: <20161018182843.xczrxsa2yd47pnru@alvherre.pgsql>
References: <20161018182843.xczrxsa2yd47pnru@alvherre.pgsql>
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On 10/18/2016 11:28 AM, Alvaro Herrera wrote:
> Vacuuming presents an additional challenge: in order to remove index
> items from an indirect index, it's critical to scan the PK index first
> and collect the PK values that are being removed. Then scan the
> indirect index and remove any items that match the PK items removed.
> This is a bit problematic because of the additional memory needed to
> store the array of PK values. I haven't implemented this yet.
As a whole I think the idea is interesting but the above scares me. Are
we trading initial performance gains for performance degradation through
maintenance? Since autovacuum is an indeterminate launch we could have a
situation where even a medium level updated laden table becomes a source
of contentions for IO and memory resources. I don't know that we would
see issues on modern bare metal but considering our implementation space
is places like RDS and GCE now, this is a serious consideration.
Sincerely,
JD
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To: pgsql-hackers@postgresql.org
Cc: jd@commandprompt.com, alvherre@2ndquadrant.com
Subject: Re: Indirect indexes
In-Reply-To: <2f5e6c38-4103-3def-2d6a-24d6509ed34e@commandprompt.com>
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