Hi Ian,
> On 26. Feb, 2020, at 01:38, Ian Barwick <ian.barw...@2ndquadrant.com> wrote:
>
> Assuming the standby/replica is created using pg_basebackup, you can use the
> -T/--tablespace-mapping option to remap the tablespace directories.
no, with Patroni, replicas are always initiated by Patroni. Patroni copies the
whole PGDATA including everything (postgresql.conf, etc.) in it to the replica
site. When launching Patroni for the first time, all you need is its yaml
configuration file and an empty PGDATA. It then will copy the whole master's
PGDATA as is, launch the replica database cluster and start replication.
Even if Patroni uses pg_basebackup internally (which I assume it does), there
is no way to pass parameters to it.
Then you can stop the Patroni process on the replica site which in turn takes
the replica database cluster down, make some configuration changes and launch
it again. You can of course only make changes to things which don't get
replicated all over again or are managed by Patroni itself. This is, how I set
up individual archive destinations for each replication member because the
initial archive destination of course is replicated, and thus identical, when
Patroni builds the replica database cluster.
Tablespace mapping just creates the links to the directories in
${PGDATA}/pg_tblspc to a different location. And since pg_basebackup isn't
used, there is no way to do that. But I can do that by hand. That is not the
problem.
The problem is that PostgreSQL keeps the tablespace location inside the
database and not in some config file. If the latter would be the case then I
could just as well set it individually per node as I can with the archive
destination.
So, the tablespace location is always /data/pg01a/ts, even on the replica site
where it should be /data/pg01b/ts. Hence, on my local cluster, the replica site
'b' always uses the tablespace directory (and thus the files) of the master 'a'.
Cheers,
Paul
