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From: Craig McIlwee <craigm@vt.edu>
Date: Thu, 7 Nov 2024 14:42:01 -0500
Message-ID: <CAGqBcTb+O8Oafa+Oa_Q8viVo+iNRehsXTjM58iQrO=c=+RjhJA@mail.gmail.com>
Subject: Re: Trouble using pg_rewind to undo standby promotion
To: =?UTF-8?Q?Torsten_F=C3=B6rtsch?= <tfoertsch123@gmail.com>
Cc: pgsql-general@lists.postgresql.org
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>
>
>> Are you archiving WAL on the promoted machine in a way that your
>> restore_command can find it? Check archive_command and archive_mode on the
>> promoted machine.
>>
>
> No, the promoted machine is not archiving.  How should that work?  Is it
> OK for a log shipping standby that uses restore_command to also push to the
> same directory with an archive_command or would that cause issues of trying
> to read and write the same file simultaneously during WAL replay?  Or
> should I be setting up an archive_command that pushes to a separate
> directory and have a restore_command that knows to check both locations?
>
> Hmm, as I write that out, I realize that I could use archive_mode = on
> instead of archive_mode = always to avoid the potential for read/write
> conflicts during WAL replay.  I can try this later and report back.
>

Setting archive_mode = on and a restore_command that reads from the WAL
archive did the trick.  With those changes in place, I was able to
successfully run pg_rewind and get the promoted standby back onto timeline
1.  Thanks for the tips.

Craig

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<div dir=3D"ltr"><div class=3D"gmail_quote"><blockquote class=3D"gmail_quot=
e" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204)=
;padding-left:1ex"><div dir=3D"ltr"><div class=3D"gmail_quote"><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"><div dir=3D"ltr"><div><br></div><div>=
Are you archiving WAL on the promoted machine in a way that your restore_co=
mmand can find it? Check archive_command and archive_mode on the promoted m=
achine.</div></div></blockquote><div><br></div><div>No, the promoted machin=
e is not archiving.=C2=A0 How should that work?=C2=A0 Is it OK for a log sh=
ipping standby that uses restore_command to also push to the same directory=
 with an archive_command or would that cause issues of trying to read and w=
rite the same file simultaneously during WAL replay?=C2=A0 Or should I be s=
etting up an archive_command that pushes to a separate directory and have a=
 restore_command that knows to check both locations?</div><div><br></div><d=
iv>Hmm, as I write that out, I realize that I could use archive_mode =3D on=
 instead of archive_mode =3D always to avoid the potential for read/write c=
onflicts during WAL replay.=C2=A0 I can try this later and report back.</di=
v></div></div></blockquote><div><br></div><div>Setting archive_mode =3D on =
and a restore_command that reads from the WAL archive did the trick.=C2=A0 =
With those changes in place, I was able to successfully run pg_rewind and g=
et the=C2=A0promoted standby back onto timeline 1.=C2=A0 Thanks for the tip=
s.</div><div><br></div><div>Craig</div></div></div>

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