From 20b254f9c2379833688a46581a8bebf07280e818 Mon Sep 17 00:00:00 2001 From: Amit Khandekar Date: Thu, 16 Jan 2020 10:05:16 +0530 Subject: [PATCH v6 5/5] Doc changes describing details about logical decoding on standby. --- doc/src/sgml/logicaldecoding.sgml | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml index bce6d379bf..745c65ff02 100644 --- a/doc/src/sgml/logicaldecoding.sgml +++ b/doc/src/sgml/logicaldecoding.sgml @@ -248,6 +248,24 @@ $ pg_recvlogical -d postgres --slot=test --drop-slot may consume changes from a slot at any given time. + + A logical replication slot can also be created on a hot standby. To prevent + VACUUM from removing required rows from the system + catalogs, hot_standby_feedback should be set on the + standby. In spite of that, if any required rows get removed, the slot gets + dropped. Existing logical slots on standby also get dropped if wal_level + on primary is reduced to less than 'logical'. + + + + For a logical slot to be created, it builds a historic snapshot, for which + information of all the currently running transactions is essential. On + primary, this information is available, but on standby, this information + has to be obtained from primary. So, slot creation may wait for some + activity to happen on the primary. If the primary is idle, creating a + logical slot on standby may take a noticeable time. + + Replication slots persist across crashes and know nothing about the state -- 2.20.1