Re: Estimating wal_keep_size

On Wed, Jun 16, 2021 at 05:36:24PM -0700, Dean Gibson (DB Administrator) wrote:
> Is this reasonable thinking?
>
> I'd think that one would want a *wal_keep_size* to cover the pending updates
> while the standby server might be unavailable, however long one might
> anticipate that would be.

It's usually a better approach to use a replication slot, to keep all the
required WAL files, and only when needed. See
https://www.postgresql.org/docs/current/warm-standby.html#STREAMING-REPLICATION-SLOTS
for more details.

Note that a replication slot will keep all WAL files, which might eventually
lead to an outage if the standby doesn't come back before the filesystem
containing the logs get full. You can cap the maximum amount of retained WAL
filed since pg 13 using max_slot_wal_keep_size, see
https://www.postgresql.org/docs/current/runtime-config-replication.html#GUC-MAX-SLOT-WAL-KEEP-SIZE.