On Fri, Nov 13, 2020 at 7:37 PM Laurenz Albe <laurenz.albe@xxxxxxxxxxx> wrote:
On Fri, 2020-11-13 at 15:24 +0200, Radoslav Nedyalkov wrote:
> On a very busy master-standby setup which runs typical olap processing -
> long living , massive writes statements, we're getting on the standby:
>
> ERROR: canceling statement due to conflict with recovery
> FATAL: terminating connection due to conflict with recovery
>
> The weird thing is that cancellations happen usually after standby has experienced
> some huge delay(2h), still not at the allowed maximum(3h). Even recently run statements
> got cancelled when the delay is already at zero.
>
> Sometimes the situation got relaxed after an hour or so.
> Restarting the server instantly helps.
>
> It is pg11.8, centos7, hugepages, shared_buffers 196G from 748G.
>
> What phenomenon could we be facing?
Hard to say. Perhaps an unusual kind of replication conflict?
What is in "pg_stat_database_conflicts" on the standby server?
db01=# select * from pg_stat_database_conflicts;
datid | datname | confl_tablespace | confl_lock | confl_snapshot | confl_bufferpin | confl_deadlock -------+-----------+------------------+------------+----------------+-----------------+----------------
13877 | template0 | 0 | 0 | 0 | 0 | 0
16400 | template1 | 0 | 0 | 0 | 0 | 0
16402 | postgres | 0 | 0 | 0 | 0 | 0
16401 | db01 | 0 | 0 | 51 | 0 | 0
(4 rows)
On a freshly restarted standby we've just got similar behaviour after a 2 hours delay and a slow catch-up.
confl_snapshots is 51 and we have exactly the same number cancelled statements.
