Message-ID: <1f38ffb000b9ead35702a63191c28f36e259c7d1.camel@cybertec.at>
Subject: Re: Documentation for initdb option --waldir
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: "David G. Johnston" <david.g.johnston@gmail.com>, t.herlo@proventa.de,
	pgsql-docs@lists.postgresql.org
Date: Thu, 27 Mar 2025 11:32:18 +0100
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On Wed, 2025-03-26 at 17:34 -0700, David G. Johnston wrote:
> +  <para>
> +   The <filename>pg_wal</filename> subdirectory will always exist within=
 the
> +   data directory.  This is where <productname>PostgreSQL</productname>
> +   sends its write-ahead log (<acronym>WAL</acronym>) files.
> +   Specifying the <option>--waldir</option> option turns this subdirecto=
ry entry
> +   into a symbolic link. In general, this is only useful if the remote l=
ocation
> +   is on a different physical device.  An existing directory must be emp=
ty and
> +   should not be a mount point.  The directory will be created
> +   (including missing parents) if necessary.
> +  </para>

I think that it is very valuable to have WAL on a different file system on =
the
same storage device.  The idea is that growing data files cannot exhaust th=
e
space available for WAL.

How about this:

    There is always a <filename>pg_wal</filename> within the data directory=
.
    By default, it is a directory where <productname>PostgreSQL</productnam=
e>
    places its write-ahead log (<acronym>WAL</acronym>) segment files.  If
    you create the <acronym>WAL</acronym> location somewhere else using the=
 option
    <option>--waldir</option>, <filename>pg_wal</filename> will be created =
as
    a symbolic link pointing to that <acronym>WAL</acronym> location.
    If the directory already exists, it must be empty and should not be a m=
ount
    point.  The directory will be created (including missing parents) if ne=
cessary.

Yours,
Laurenz Albe