On Wed, May 17, 2023 at 08:16:41AM +0200, Laurenz Albe wrote: > On Tue, 2023-05-16 at 19:35 +0200, hubert depesz lubaczewski wrote: > > > I'm working on a workaround for a bug in Pg > > > (https://www.postgresql.org/message-id/flat/Yz2hivgyjS1RfMKs%40depesz.com) > > > I want to create replication slot, and advance is manually, keeping it > > > always a bit lagging behind real replication slot. > > > > > > I can create slot, no problem: > > > select pg_create_logical_replication_slot('depesz', 'test_decoding'); > > > and then I can, theoretically, advance it to whatever position with > > > select * from pg_replication_slot_advance('depesz', '...'); > > > > > > *BUT* - it changes only confirmed_flush_lsn, leaving restart_lsn as it > > > was. > > > > > > How can I advance restart_lsn of a slot? > > > > > > Generally my idea is to get lsn from real replication slot, subtract, > > > let's say 1GB from it, and advance my "fake slot" to this value, this > > > keeping always buffer of 1GB in case the bug with removed wal happened > > > again. > > > > > > I will be doing this on Pg12, which can limit my options, but perhaps > > > there is some way to do it via plain(ish) SQL ? > > > > if doing it via SQL is not an option, is there any way to have > > replication slot and modify it's restart_lsn, regardless of whether it > > will b e physical, or logical, and what tool shoudl I use. > > > > I tried with pg_recvlogical, and read > > https://www.postgresql.org/docs/current/protocol-replication.html but > > I don't see how I can make restart_lsn advance to anything. > > You could shutdown the server and edit the file in "pg_replslot" with > a hex editor. Not very convenient, and you'd have to study the source > to understand the format of the file. OK. Shutting down production server every 5 minutes to advance the slot isn't really an option. How do "normal" wal consumers update restart_lsn? Is there a reason why it can't be done using pg_rec(eive|v)* ? Best regards, depesz
