Re: Time delayed LR (WAS Re: logical replication restrictions)

On Mon, Mar 06, 2023 at 07:27:59PM +0300, Önder Kalacı wrote:
> On the other hand, we already have a similar problem with
> recovery_min_apply_delay combined with hot_standby_feedback [1].
> So, that probably is an acceptable trade-off for the pgsql-hackers.
> If you use this feature, you should be even more careful.

Yes, but it's possible to turn off hot_standby_feedback so that you don't
incur bloat on the primary.  And you don't need to store hours or days of
WAL on the primary.  I'm very late to this thread, but IIUC you cannot
avoid blocking VACUUM with the proposed feature.  IMO the current set of
trade-offs (e.g., unavoidable bloat and WAL buildup) would make this
feature virtually unusable for a lot of workloads, so it's probably worth
exploring an alternative approach.  In any case, we probably shouldn't rush
this into v16 in its current form.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com