Re: pg_waldump: support decoding of WAL inside tarfile

From: Tomas Vondra <tomas(at)vondra(dot)me>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
Cc: 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: 2026-03-28 22:57:37
Message-ID: 97a382c0-1f19-4ea0-951f-e37e6abc34a3@vondra.me
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On 3/28/26 23:36, Tom Lane wrote:
> I wrote:
>> However ... I do not find any indication in the GNU tar docs
>> that it produces sparse files by default. It looks like you
>> need to say -S/--sparse to make that happen. Maybe you have
>> a version that's been hacked to make that the default?
>
> Bleah. Digging in the man pages at freebsd.org, I read
>
> --read-sparse
> (c, r, u modes only) Read sparse file information from disk.
> This is the reverse of --no-read-sparse and the default behav-
> ior.
>
> It's apparently been there and been default since FreeBSD 13.1.
> This leads one to wonder how come BF member dikkop is managing
> to run this test successfully. I speculate that it's using a
> filesystem type that doesn't do sparse files (cc'ing Vondra
> for confirmation on that).
>

It's running on ufs. But I think the explanation is very simple. We had
a short power outage on Thursday, and the FreeBSD machine failed to boot
properly after the power was restored. IIUC this test is new, right?

I fixed the machine, it'll start running the tests in a couple minutes.

regards

--
Tomas Vondra

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