Create replication slot in pg_basebackup if requested and not yet present

From: Michael Banck <michael(dot)banck(at)credativ(dot)de>
To: Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Create replication slot in pg_basebackup if requested and not yet present
Date: 2017-03-19 10:21:47
Views: Raw Message | Whole Thread | Download mbox | Resend email
Lists: pgsql-hackers


with the default configuration improvements so far for 10, it seems to
be very easy to setup streaming replication (at least locally):

$ initdb --pgdata=data1
$ pg_ctl --pgdata=data1 start
$ pg_basebackup --pgdata=data2 --write-recovery-conf
$ sed -i -e 's/^#port.=.5432/port = 5433/' \
> -e 's/^ = on/' \
> data2/postgresql.conf
$ pg_ctl --pgdata=data2 start

(there might be a case for having hot_standby=on by default, but I think
that got discussed elsewhere and is anyway a different thread).

However, the above does not use replication slots, and if you want to do
so, you get:

$ pg_basebackup --pgdata=data2 --write-recovery-conf --slot=pg2
2017-03-19 11:04:37.978 CET [25362] ERROR: replication slot "pg2" does
not exist
pg_basebackup: could not send replication command "START_REPLICATION":
ERROR: replication slot "pg2" does not exist
pg_basebackup: child process exited with error 1
pg_basebackup: removing data directory "data2"

The error message is clear enough, but I wonder whether people will
start writing streaming replication tutorials just glossing over this
because it's one more step to run CREATE_REPLICATION_SLOT manually.

So I propose the attached tiny patch to just create the slot (if it does
not exist already) in pg_basebackup, somewhat similar to what
pg_receivewal does, albeit unconditionally, if the user explicitly
requested a slot:

$ pg_basebackup --pgdata=data2 --write-recovery-conf --slot=pg2
$ echo $?
$ psql -c "DROP_REPLICATION_SLOT pg2" "host= port=5432 replication=database user=mba dbname=postgres"

This would get us somewhat closer to near zero-config replication, in my
opinion. Pardon me if that was discussed already and shot down



Michael Banck
Projektleiter / Senior Berater
Tel.: +49 2166 9901-171
Fax: +49 2166 9901-100
Email: michael(dot)banck(at)credativ(dot)de

credativ GmbH, HRB Mönchengladbach 12080
USt-ID-Nummer: DE204566209
Trompeterallee 108, 41189 Mönchengladbach
Geschäftsführung: Dr. Michael Meskes, Jörg Folz, Sascha Heuer

Attachment Content-Type Size
0001-Create-replication-slot-in-pg_basebackup-if-requeste.patch text/x-patch 1.2 KB


Browse pgsql-hackers by date

  From Date Subject
Next Message Pavel Stehule 2017-03-19 11:32:50 Re: PoC plpgsql - possibility to force custom or generic plan
Previous Message Tatsuo Ishii 2017-03-19 10:18:48 Re: [HACKERS] Questionable tag usage