On Tue, Nov 8, 2022 at 1:36 AM Amit Kapila <amit.kapil...@gmail.com> wrote:
> On Tue, Nov 8, 2022 at 12:08 PM sirisha chamarthi > <sirichamarth...@gmail.com> wrote: > > > > On Fri, Nov 4, 2022 at 11:02 PM Amit Kapila <amit.kapil...@gmail.com> > wrote: > >> > >> On Fri, Nov 4, 2022 at 1:40 PM sirisha chamarthi > >> <sirichamarth...@gmail.com> wrote: > >> > > >> > A replication slot can be lost when a subscriber is not able to catch > up with the load on the primary and the WAL to catch up exceeds > max_slot_wal_keep_size. When this happens, target has to be reseeded > (pg_dump) from the scratch and this can take longer. I am investigating the > options to revive a lost slot. > >> > > >> > >> Why in the first place one has to set max_slot_wal_keep_size if they > >> care for WAL more than that? > > > > Disk full is a typical use where we can't wait until the logical slots > to catch up before truncating the log. > > > > Ideally, in such a case the subscriber should fall back to the > physical standby of the publisher but unfortunately, we don't yet have > a functionality where subscribers can continue logical replication > from physical standby. Do you think if we had such functionality it > would serve our purpose? > Don't think streaming from standby helps as the disk layout is expected to remain the same on physical standby and primary. > >> If you have a case where you want to > >> handle this case for some particular slot (where you are okay with the > >> invalidation of other slots exceeding max_slot_wal_keep_size) then the > >> other possibility could be to have a similar variable at the slot > >> level but not sure if that is a good idea because you haven't > >> presented any such case. > > > > IIUC, ability to fetch WAL from the archive as a fall back mechanism > should automatically take care of all the lost slots. Do you see a need to > take care of a specific slot? > > > > No, I was just trying to see if your use case can be addressed in some > other way. BTW, won't copying the WAL again back from archive can lead > to a disk full situation. > The idea is to download the WAL from archive on demand as the slot requires them and throw away the segment once processed. > > -- > With Regards, > Amit Kapila. >
