Hi Troels, The question is how long your pg_dump run takes, as that is the duration you need to have the delay set to. After the delay runs out, the system will start applying WAL again, and to do that, it will end all queries that run against the system/tables to allow for the apply to take place. Alternatively, you can indeed activate hot_standby_feedback, which will sort of do the same, and retain WAL on the primary, both cases require space monitoring to ensure you continue to have enough free space for the accumulating WAL.
Cheers, Jan > On 29 Oct 2026, at 10:45, Troels Arvin <[email protected]> wrote: > > Hello, > > I have a setup with a rather busy and semi-large primary Postgres server > which uses physical streaming replication to a secondary server. The > secondary server is to be used for read-only queries (reporting), and I've > starting running pg_dumps towards the secondary. > > I now run into error messages like the following when pg_dump works against > the secondary: > > pg_dump: error: Dumping the contents of table "sometable" failed: > PQgetResult() failed. > pg_dump: detail: Error message from server: ERROR: canceling statement due to > conflict with recovery > DETAIL: User query might have needed to see row versions that must be removed. > pg_dump: detail: Command was: COPY someschema.sometable (col1, col2, col3) TO > stdout; > > I have tried setting > max_standby_streaming_delay = 5min > (Default is 30s.) That doesn't help. > > I'm wondering: Should I further raise max_standby_streaming_delay, for > example to 30min? > > Or should I set hot_standby_feedback to "on"? > https://postgresqlco.nf/doc/en/param/hot_standby_feedback/ recommends it stay > off for my use case: "Turn it off for a replica which does long-running > reports and is allowed to lag." But having heard > https://postgres.fm/episodes/hot_standby_feedback I get the impression > hot_standby_feedback should almost always be on when using streaming > replication. > > Would it make sense with a combination, i.e. setting > max_standby_streaming_delay to 10 minutes and activating hot_standby_feedback? > > -- > Kind regards, > Troels Arvin > > > > > >
