Pursuant to a comment I made a few months ago[1], I propose the attached changes to replication slots documentation. In essence, I want to explain that replication slots are good, and the max_size GUC, before moving on to explain that the other methods are worse.
Thanks [1] https://postgr.es/m/20230413111838.e7yxke2dtwrxw3qy@alvherre.pgsql -- Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/ "Entristecido, Wutra (canción de Las Barreras) echa a Freyr a rodar y a nosotros al mar"
>From c003a2c6ae8d1c177fbd4c1f77b428c5ad24e705 Mon Sep 17 00:00:00 2001 From: Alvaro Herrera <alvhe...@alvh.no-ip.org> Date: Fri, 19 May 2023 20:15:52 +0200 Subject: [PATCH] Rework paragraphs in replication slots docs Discussion: https://postgr.es/m/20230413111838.e7yxke2dtwrxw3qy@alvherre.pgsql --- doc/src/sgml/high-availability.sgml | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/doc/src/sgml/high-availability.sgml b/doc/src/sgml/high-availability.sgml index 9dd52ff275..887366bdec 100644 --- a/doc/src/sgml/high-availability.sgml +++ b/doc/src/sgml/high-availability.sgml @@ -930,25 +930,27 @@ primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass' <link linkend="hot-standby-conflict">recovery conflict</link> even when the standby is disconnected. </para> + <para> + Beware that replication slots can retain so many WAL segments that they + fill up the space allocated for <literal>pg_wal</literal>. + <xref linkend="guc-max-slot-wal-keep-size"/> can be used to limit the size + of WAL files retained by replication slots. + </para> <para> In lieu of using replication slots, it is possible to prevent the removal of old WAL segments using <xref linkend="guc-wal-keep-size"/>, or by storing the segments in an archive using <xref linkend="guc-archive-command"/> or <xref linkend="guc-archive-library"/>. - However, these methods often result in retaining more WAL segments than + A disadvantage of these methods is that they + often result in retaining more WAL segments than required, whereas replication slots retain only the number of segments - known to be needed. On the other hand, replication slots can retain so - many WAL segments that they fill up the space allocated - for <literal>pg_wal</literal>; - <xref linkend="guc-max-slot-wal-keep-size"/> limits the size of WAL files - retained by replication slots. + known to be needed. </para> <para> Similarly, <xref linkend="guc-hot-standby-feedback"/> on its own, without also using a replication slot, provides protection against relevant rows being removed by vacuum, but provides no protection during any time period - when the standby is not connected. Replication slots overcome these - disadvantages. + when the standby is not connected. </para> <sect3 id="streaming-replication-slots-manipulation"> <title>Querying and Manipulating Replication Slots</title> -- 2.39.2
