On 24/01/18 12:28, Craig Ringer wrote: > On 24 January 2018 at 22:41, Ryan Murphy <ryanfmur...@gmail.com > <mailto:ryanfmur...@gmail.com>> wrote: > > Hello hackers, > > I'm experimenting with Logical Replication. > (https://www.postgresql.org/docs/10/static/logical-replication.html > <https://www.postgresql.org/docs/10/static/logical-replication.html>) > What I'm trying to do may be impossible l but just wanted to ask here. > > I'm trying to do logical replication from one database to another > within the same server. > Ultimately I want to do it between servers but was just trying this > for connection simplicity (same host etc). > > *Details:* > > I have a postgres server running (11devel) with a database, call it db1. > I created a new database on the same server, call it db2. > I also created a test table, call it table1: > CREATE TABLE table1 (id serial primary key, name text, tags text[]); > > On both databases I ran: > ALTER SYSTEM SET wal_level = logical; > > (not sure if that's redundant because it's the same server?) > > On db1 I ran: > CREATE PUBLICATION test_pub FOR TABLE table1; > On db2 I ran: > CREATE SUBSCRIPTION test_sub > CONNECTION 'host=127.0.0.1 dbname=db1 user=xxxxxx password=xxxxxx' > PUBLICATION test_pub; > > It just hangs. > > > You must create the replication slot manually in advance.
Indeed. > I thought that was documented as a caveat. It is documented in CREATE SUBSCRIPTION docs. > For that matter, wasn't there > discussion of detecting that situation and telling the user about the > problem gracefully? Don't know if we ever got to doing that but seems not. We didn't find clean way of detecting this (being sure this is the case involves a lot of shmem gymnastics and process interlocking, not to mention the code layering does not really work for it). -- Petr Jelinek http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
