Re: pg_waldump: support decoding of WAL inside tarfile

From: Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
To: Tomas Vondra <tomas(at)vondra(dot)me>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andres Freund <andres(at)anarazel(dot)de>, Michael Paquier <michael(at)paquier(dot)xyz>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Amul Sul <sulamul(at)gmail(dot)com>, Zsolt Parragi <zsolt(dot)parragi(at)percona(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>, Anthonin Bonnefoy <anthonin(dot)bonnefoy(at)datadoghq(dot)com>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Jakub Wartak <jakub(dot)wartak(at)enterprisedb(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: pg_waldump: support decoding of WAL inside tarfile
Date: 2026-03-29 22:20:24
Message-ID: CA+hUKGJk4uw5Cdx8+m8YPWmDVB_TtrnMJd24_vQHQDXQz9Qzfw@mail.gmail.com
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On Mon, Mar 30, 2026 at 11:11 AM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> ... so that's a yes, lseek sees holes that we didn't ask it to make,

Oops, sorry, I wrote that email too fast and got my examples mixed up,
BTFS actually *doesnt* do that automatically, that was of course a
trace showing a file with explicitly made holes. So this is probably
be a ZFS-only issue unless you're using wal_init_zero=0, and then any
file system could result in PAX-sparse-format tarballs, but even then
only if you use non-default switches that in practice no one will use
with GNU tar, or if you use BSD tar. So in practice this is a
FreeBSD-only issue.

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