From: | Greg Stark <stark(at)mit(dot)edu> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Greg Stark <gsstark(at)mit(dot)edu>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, decibel <decibel(at)decibel(dot)org>, "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>, "jd(at)commandprompt(dot)com" <jd(at)commandprompt(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Aidan Van Dyk <aidan(at)highrise(dot)ca>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Block-level CRC checks |
Date: | 2009-12-06 01:23:00 |
Message-ID: | 1F996909-8508-4F91-B44C-8B07F9FB68F7@mit.edu |
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Lists: | pgsql-hackers |
It can save space because the line pointers have less alignment
requirements. But I don't see any point in the current state.
--
Greg
On 2009-12-04, at 3:48 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Greg Stark <gsstark(at)mit(dot)edu> writes:
>> I'm not sure why I said "including ctid". We would have to move
>> everything transactional to the line pointer, including xmin, xmax,
>> ctid, all the hint bits, the updated flags, hot flags, etc. The only
>> things left in the tuple header would be things that have to be there
>> such as HAS_OIDS, HAS_NULLS, natts, hoff, etc. It would be a pretty
>> drastic change, though a fairly logical one. I recall someone
>> actually
>> submitted a patch to separate out the transactional bits anyways a
>> while back, just to save a few bytes in in-memory tuples. If we could
>> save on disk-space usage it would be a lot more compelling. But it
>> doesn't look to me like it really saves enough often enough to be
>> worth so much code churn.
>
> It would also break things for indexes, which don't need all that
> stuff
> in their line pointers.
>
> More to the point, moving the same bits to someplace else on the page
> doesn't save anything at all.
>
> regards, tom lane
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