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Re: Hot Standby and VACUUM FULL

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Simon Riggs <simon(at)2ndQuadrant(dot)com>
Cc: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Hot Standby and VACUUM FULL
Date: 2010-02-01 15:27:21
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Lists: pgsql-hackers
Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> On Mon, 2010-02-01 at 10:06 -0500, Tom Lane wrote:
>> the assumption that the file is less than one disk block,
>> it should be just as atomic as pg_control updates are.

> IIRC there were 173 relations affected by this. 4 bytes each we would
> have more than 512 bytes.

Where in the world did you get that number?

There are currently 29 shared relations (counting indexes), and 13
nailed local relations, which would go into a different map file.
I'm not sure if the set of local catalogs requiring the map treatment
is exactly the same as what's presently nailed, but that's probably
a good approximation.

At 8 bytes each (OID + relfilenode), we could fit 64 map entries in
a standard disk sector --- let's say 63 so there's room for a header.
So, barring more-than-doubling of the number of shared catalogs,
there's not going to be a problem.

			regards, tom lane

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