From: Jim Nasby <Jim.Nasby@BlueTreble.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Petr Jelinek <petr@2ndquadrant.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: hlinnaka@iki.fi
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: Sawada Masahiko <sawada.mshk@gmail.com>
Cc: Greg Stark <stark@mit.edu>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Cc: Jeff Janes <jeff.janes@gmail.com>
Subject: Re: Reducing tuple overhead
Date: Mon, 27 Apr 2015 16:01:13 -0500
Message-ID: <553EA399.1010508@BlueTreble.com> (raw)
In-Reply-To: <CAA4eK1KbqMicXYFo6MCp7nnOfjkuqyx071c+sAm0c+ftAKSCBw@mail.gmail.com>
References: <20150423162429.GG3055@alap3.anarazel.de>
<553921B1.7080204@2ndquadrant.com>
<5539491C.6040405@BlueTreble.com>
<CAA4eK1+R2f+woEsu_Woj6AgoZE6LRxYCVg5kXiC3snKSkxHmFQ@mail.gmail.com>
<553AA753.9010103@BlueTreble.com>
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On 4/25/15 12:12 AM, Amit Kapila wrote:
> > ... which isn't possible. You can not go from a heap tuple to an
> index tuple.
>
> We will have the access to index value during delete, so why do you
> think that we need linkage between heap and index tuple to perform
> Delete operation? I think we need to think more to design Delete
> .. by CTID, but that should be doable.
The problem with just having the value is that if *anything* changes
between how you evaluated the value when you created the index tuple and
when you evaluate it a second time you'll corrupt your index. This is
actually an incredibly easy problem to have; witness how we allowed
indexing timestamptz::date until very recently. That was clearly broken,
but because we never attempted to re-run the index expression to do
vacuuming at least we never corrupted the index itself.
> > This has been discussed in the past.
>
> I have tried to search in archive, but not getting what is the exact
> problem.
Unfortunately I can't find prior discussion now either... :/
--
Jim Nasby, Data Architect, Blue Treble Consulting
Data in Trouble? Get it in Treble! http://BlueTreble.com
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Cc: Jim.Nasby@BlueTreble.com, amit.kapila16@gmail.com, petr@2ndquadrant.com, andres@anarazel.de, hlinnaka@iki.fi, robertmhaas@gmail.com, bruce@momjian.us, sawada.mshk@gmail.com, stark@mit.edu, jeff.janes@gmail.com
Subject: Re: Reducing tuple overhead
In-Reply-To: <553EA399.1010508@BlueTreble.com>
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