From 3e300822777f89907cf0abd7c90f03cabdd4b205 Mon Sep 17 00:00:00 2001 From: bdrouvotAWS Date: Tue, 23 Mar 2021 16:15:35 +0000 Subject: [PATCH v13 5/5] Doc changes describing details about logical decoding. --- doc/src/sgml/logicaldecoding.sgml | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) 100.0% doc/src/sgml/ diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml index 80eb96d609..050befa55e 100644 --- a/doc/src/sgml/logicaldecoding.sgml +++ b/doc/src/sgml/logicaldecoding.sgml @@ -297,6 +297,24 @@ postgres=# select * from pg_logical_slot_get_changes('regression_slot', NULL, NU 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 -- 2.18.4