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Re: Reduction in WAL for UPDATEs

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Gregory Stark <stark(at)enterprisedb(dot)com>
Cc: "Kenneth Marshall" <ktm(at)rice(dot)edu>, pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: Reduction in WAL for UPDATEs
Date: 2007-03-28 15:17:32
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Lists: pgsql-hackers
Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> A lot of the recently proposed changes don't really fit in the
> "optimizations" category very well at all. I think of them more as
> "avoiding pitfalls".

Well, we can't put a major amount of complexity into the system for
each possible "pitfall".

> This one is similar, if you keep a bunch of static data attached to
> some small dynamic data your WAL and table bloats.

Actually, PG does extremely well on that in the situation where the
static data is *really* wide, ie, wide enough to be toasted out-of-line.
Simon's proposal will only help for an intermediate range of situations
where the row is wide but not very wide.

It strikes me that a more useful solution might come from the recent
discussions about offering more user control of per-column toasting
decisions.  Or maybe we just need to revisit the default toast
thresholds --- AFAIR there has never been any significant study of
the particular values that Jan picked originally.

			regards, tom lane

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