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Re: Catalog/Metadata consistency during changeset extraction from wal

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "David Fetter" <david(at)fetter(dot)org>,<pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Catalog/Metadata consistency during changeset extraction from wal
Date: 2012-06-26 22:05:27
Message-ID: 4FE9EBD70200002500048B40@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-hackers
David Fetter <david(at)fetter(dot)org> wrote:
> On Mon, Jun 25, 2012 at 01:50:54PM -0500, Kevin Grittner wrote:
 
>> One fine point regarding before and after images -- if a value
>> doesn't change in an UPDATE, there's no reason to include it in
>> both the BEFORE and AFTER tuple images, as long as we have the
>> null column bitmaps -- or some other way of distinguishing
>> unchanged from NULL.  (This could be especially important when
>> the unchanged column was a 50 MB bytea.)
> 
> How about two bitmaps: one telling which columns are actually
> there, the other with NULLs?
 
There are quite a few ways that could be done, but I suspect
Álvaro's idea is best:
 
http://archives.postgresql.org/message-id/1340654533-sup-5535@alvh.no-ip.org
 
In any event, it sounds like Andres wants to keep it as simple as
possible for the moment, and just include both tuples in their
entirety.  Hopefully that is something which can be revisited before
the last CF.
 
-Kevin

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