On Tue, Jun 23, 2020 at 7:47 AM Fujii Masao <masao.fu...@oss.nttdata.com> wrote: > > On 2020/06/23 10:10, Kyotaro Horiguchi wrote: > > At Mon, 22 Jun 2020 22:02:51 +0900, Fujii Masao > > <masao.fu...@oss.nttdata.com> wrote in > >> > >>> I feel such a function is good to have but I am not sure if there is a > >>> need to tie it with the removal of min_safe_lsn column. > >> > >> We should expose the LSN calculated from > >> "the current WAL LSN - max(wal_keep_segments * 16MB, > >> max_slot_wal_keep_size)"? > >> This indicates the minimum LSN of WAL files that are guaraneed to be > >> currently retained by wal_keep_segments and max_slot_wal_keep_size. > >> That is, if checkpoint occurs when restart_lsn of replication slot is > >> smaller than that minimum LSN, some required WAL files may be removed. > >> So DBAs can periodically monitor and compare restart_lsn and that > >> minimum > >> LSN. If they see frequently that difference of those LSN is very > >> small, > >> they can decide to increase wal_keep_segments or > >> max_slot_wal_keep_size, > >> to prevent required WAL files from being removed. Thought? > > > > I'm not sure about the consensus here about showing that number in the > > view. It is similar to "remain" in the earlier versions of this patch > > but a bit simpler. It would be usable in a similar way. I can live > > with either numbers. > > It's useless to display this value in each replication slot in the view. > I'm thinking to expose it as a function. >
Having a separate function for this seems like a good idea but can we consider displaying it in a view like pg_stat_replication_slots as we are discussing a nearby thread to have such a view for other things. I think ultimately this information is required to check whether some slot can be invalidated or not, so having it displayed along with other slot information might not be a bad idea. [1] - https://www.postgresql.org/message-id/CAA4eK1Jyh4qgdnxzV4fYuk9GiXLb%3DUz-6o19E2RfiN8MPmUu3A%40mail.gmail.com -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
