Re: Lowering the default wal_blocksize to 4K

From: Andres Freund <andres(at)anarazel(dot)de>
To: Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Robert Haas <robertmhaas(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
Subject: Re: Lowering the default wal_blocksize to 4K
Date: 2023-10-11 22:16:33
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On 2023-10-11 16:09:21 +0200, Matthias van de Meent wrote:
> On Wed, 11 Oct 2023 at 01:29, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > > After that we'll only have the system ID left from the extended
> > > header, which we could store across 2 pages in the (current) alignment
> > > losses of xlp_rem_len - even pages the upper half, uneven pages the
> > > lower half of the ID. This should allow for enough integrity checks
> > > without further increasing the size of XLogPageHeader in most
> > > installations.
> >
> > I doubt that that's a good idea - what if there's just a single page in a
> > segment? And there aren't earlier segments? That's not a rare case, IME.
> Then we'd still have 50% of a system ID which we can check against for
> any corruption. I agree that it increases the chance of conflics, but
> it's still strictly better than nothing at all.

A fair point - I somehow disregarded that all bits in the system id are
equally meaningful.


Andres Freund

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