Re: Estimating wal_keep_size

On 2021-06-16 18:02, Julien Rouhaud wrote:
> 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 files 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.

Granted, but the same question arises about the value for
max_slot_wal_keep_size.  Setting either too low risks data loss, &
setting either too high results in unnecessary disk space used.  The
question was, is the estimated VALUE reasonable under the circumstances?