On Tue, 7 Jul 2020 at 17:50, Magnus Hagander <mag...@hagander.net> wrote: > > > > On Tue, Jul 7, 2020 at 5:10 AM Amit Kapila <amit.kapil...@gmail.com> wrote: >> >> On Tue, Jul 7, 2020 at 7:07 AM Masahiko Sawada >> <masahiko.saw...@2ndquadrant.com> wrote: >> > >> > On Mon, 6 Jul 2020 at 20:45, Amit Kapila <amit.kapil...@gmail.com> wrote: >> > > >> > > > Second, as long as the unique identifier is the slot name there is no >> > > > convenient way to distinguish between the same name old and new >> > > > replication slots, so the backend process or wal sender process sends >> > > > a message to the stats collector to drop the replication slot at >> > > > ReplicationSlotDropPtr(). This strategy differs from what we do for >> > > > table, index, and function statistics. It might not be a problem but >> > > > I’m thinking a better way. >> > > > >> > > >> > > Can we rely on message ordering in the transmission mechanism (UDP) >> > > for stats? The wiki suggests [1] we can't. If so, then this might >> > > not work. >> > >> > Yeah, I'm also concerned about this. Another idea would be to have >> > another unique identifier to distinguish old and new replication slots >> > with the same name. For example, creation timestamp. And then we >> > reclaim the stats of unused slots later like table and function >> > statistics. >> > >> >> So, we need to have 'creation timestamp' as persistent data for slots >> to achieve this? I am not sure of adding creation_time as a parameter >> to identify for this case because users can change timings on systems >> so it might not be a bullet-proof method but I agree that it can work >> in general. > > > If we need them to be persistent across time like that, perhaps we simply > need to assign oids to replication slots? That might simplify this problem > quite a bit?
Yeah, I guess assigning oids to replication slots in the same way of oids in system catalogs might not work because physical replication slot can be created even during recovery. But using a monotonically-increasing integer as id seems better and straight forward. This id is not necessarily displayed in pg_repliation_slots view because the user already can use slot name as a unique identifier. Regards, -- Masahiko Sawada http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
