Hello Hackers,
At the moment one can open up a replication connection using psql and use all of the commands available on this special type of connection, except for START_REPLICATION:
$ psql -d "dbname=test replication=database"
psql (9.4.1)
Type "help" for help.
test=# IDENTIFY_SYSTEM;
systemid | timeline | xlogpos | dbname
---------------------+----------+-----------+---------
6146106447402521313 | 1 | 0/76422B0 | bw_test
(1 row)
test=# START_REPLICATION SLOT test LOGICAL 0/0;
unexpected PQresultStatus: 8
test=#
This is due to PGRES_COPY_BOTH not being handled in psql. With introduction of logical replication I think it makes sense to support this mode, for the sake of (semi-)interactive testing from psql.
For example, one could try replication from different wal positions, different output plugins and/or plugin options, w/o re-establishing the connection, interactively by editing the command directly in psql prompt, as opposed to using pg_recvlogical and editing the command line switches.
I can make a patch if there's general interest for this feature.
Cheers.
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