From: Avi Weinberg <AviW@gilat.com>
To: pgsql-generallists.postgresql.org <pgsql-general@lists.postgresql.org>
Subject: Continue Logical Replication After Master Became Slave and then
 Became Master Again
Thread-Topic: Continue Logical Replication After Master Became Slave and then
 Became Master Again
Thread-Index: AdtPGINR7zQ7kwdZQqqS2jb9IhMiXw==
Date: Sun, 15 Dec 2024 17:41:05 +0000
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Hi All,

Postgres 15.2

We have Patroni cluster with one master and two replicas.  The master is pu=
blisher (logical replication) to some subscriptions running on other cluste=
rs.  When we have a failover, the master becomes replica and one of the rep=
licas assume the role of master.  In such a case, we need to rebuild the su=
bscriptions to point to the new master.  However, to avoid that, can we jus=
t do fallback and move back to the old master assuming the following option=
s - what if:

  1.  No data was written to the database from the time of the failover unt=
il the failback
  2.  No data was written to the replicated tables (but other tables were u=
pdated) from the time of the failover until the failback
  3.  The replicated tables were updated from the time of the failover unti=
l the failback


Thanks

IMPORTANT - This email and any attachments is intended for the above named =
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<p class=3D"MsoNormal" style=3D"text-align:left;direction:ltr;unicode-bidi:=
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<p class=3D"MsoNormal" style=3D"text-align:left;direction:ltr;unicode-bidi:=
embed"><o:p>&nbsp;</o:p></p>
<p class=3D"MsoNormal" style=3D"text-align:left;direction:ltr;unicode-bidi:=
embed">Postgres 15.2
<o:p></o:p></p>
<p class=3D"MsoNormal" style=3D"text-align:left;direction:ltr;unicode-bidi:=
embed"><o:p>&nbsp;</o:p></p>
<p class=3D"MsoNormal" style=3D"text-align:left;direction:ltr;unicode-bidi:=
embed">We have Patroni cluster with one master and two replicas.&nbsp; The =
master is publisher (logical replication) to some subscriptions running on =
other clusters.&nbsp; When we have a failover,
 the master becomes replica and one of the replicas assume the role of mast=
er.&nbsp; In such a case, we need to rebuild the subscriptions to point to =
the new master.&nbsp; However, to avoid that, can we just do fallback and m=
ove back to the old master assuming the following
 options &#8211; what if:<o:p></o:p></p>
<ol style=3D"margin-top:0cm" start=3D"1" type=3D"1">
<li class=3D"MsoListParagraph" style=3D"margin-right:0cm;text-align:left;ms=
o-list:l0 level1 lfo1;direction:ltr;unicode-bidi:embed">
No data was written to the database from the time of the failover until the=
 failback<o:p></o:p></li><li class=3D"MsoListParagraph" style=3D"margin-rig=
ht:0cm;text-align:left;mso-list:l0 level1 lfo1;direction:ltr;unicode-bidi:e=
mbed">
No data was written to the replicated tables (but other tables were updated=
) from the time of the failover until the failback<o:p></o:p></li><li class=
=3D"MsoListParagraph" style=3D"margin-right:0cm;text-align:left;mso-list:l0=
 level1 lfo1;direction:ltr;unicode-bidi:embed">
The replicated tables were updated from the time of the failover until the =
failback<o:p></o:p></li></ol>
<p class=3D"MsoListParagraph" style=3D"mso-margin-top-alt:0cm;margin-right:=
0cm;margin-bottom:0cm;margin-left:36.0pt;margin-bottom:.0001pt;text-align:l=
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<o:p>&nbsp;</o:p></p>
<p class=3D"MsoListParagraph" style=3D"mso-margin-top-alt:0cm;margin-right:=
0cm;margin-bottom:0cm;margin-left:36.0pt;margin-bottom:.0001pt;text-align:l=
eft;direction:ltr;unicode-bidi:embed">
Thanks<o:p></o:p></p>
</div>
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