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From: Ron Johnson <ronljohnsonjr@gmail.com>
Date: Mon, 11 Aug 2025 09:13:38 -0400
Message-ID: <CANzqJaBG3yn7-BCgjDuUWqusKSBSsCwk1Lw+vSe26EZQRfMtXw@mail.gmail.com>
Subject: Re: Backups with filesystem snapshots
To: PostgreSQL General <pgsql-general@lists.postgresql.org>
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On Mon, Aug 11, 2025 at 9:01=E2=80=AFAM Nick Cleaton <nick@cleaton.net> wro=
te:

> If I take an instantaneous filesystem-level snapshot of the postgres
> data directory underneath a running postgres server, is that a safe
> backup without doing any pg_start_backup/pg_stop_backup ?
>
> It seems like it should be, so long as I get an atomic snapshot that
> includes both data and wal, because starting up from that snapshot
> should look the same as recovering from an unclean postgres shutdown
> due to a kernel panic.
>

We once restored a whole-system VMware snapshot to a new VM (new IP address
and everything). When I logged in, PG started up without a hiccup; it
took a couple of minutes while WALs rolled forward, but that's to be
expected.

Postgresql didn't (and doesn't) know anything about when snapshots are
taken.

--=20
Death to <Redacted>, and butter sauce.
Don't boil me, I'm still alive.
<Redacted> lobster!

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<div dir=3D"ltr"><div dir=3D"ltr">On Mon, Aug 11, 2025 at 9:01=E2=80=AFAM N=
ick Cleaton &lt;<a href=3D"mailto:nick@cleaton.net">nick@cleaton.net</a>&gt=
; wrote:</div><div class=3D"gmail_quote gmail_quote_container"><blockquote =
class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px sol=
id rgb(204,204,204);padding-left:1ex">If I take an instantaneous filesystem=
-level snapshot of the postgres<br>
data directory underneath a running postgres server, is that a safe<br>
backup without doing any pg_start_backup/pg_stop_backup ?<br>
<br>
It seems like it should be, so long as I get an atomic snapshot that<br>
includes both data and wal, because starting up from that snapshot<br>
should look the same as recovering from an unclean postgres shutdown<br>
due to a kernel panic.<br>
</blockquote></div><div><br clear=3D"all"></div><div>We once restored a who=
le-system VMware snapshot to a new=C2=A0VM (new IP address and everything).=
 When I logged in, PG started up without a hiccup; it took=C2=A0a=C2=A0coup=
le of minutes while=C2=A0WALs rolled forward,=C2=A0but that&#39;s to be exp=
ected.</div><div><br></div><div>Postgresql didn&#39;t (and doesn&#39;t) kno=
w anything about when snapshots are taken.</div><div><br></div><span class=
=3D"gmail_signature_prefix">-- </span><br><div dir=3D"ltr" class=3D"gmail_s=
ignature"><div dir=3D"ltr">Death to &lt;Redacted&gt;, and butter sauce.<div=
>Don&#39;t boil me, I&#39;m still alive.<br><div><div>&lt;Redacted&gt; lobs=
ter!</div></div></div></div></div></div>

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