Column xact_rollback from pg_stat_database gets inconsistently incremented when logical replication is being used (on publisher side).
This can be easily reproduced in latest code from master branch:
- Publisher
postgres=# select xact_commit, xact_rollback from pg_stat_database where datname = 'postgres';
-[ RECORD 1 ]-+---
xact_commit | 20
xact_rollback | 0
postgres=# insert into t1 values (1);
INSERT 0 1
postgres=# insert into t1 values (2);
INSERT 0 1
postgres=# insert into t1 values (3);
INSERT 0 1
postgres=# insert into t1 values (4);
INSERT 0 1
postgres=# insert into t1 values (5);
INSERT 0 1
postgres=# insert into t1 values (6);
INSERT 0 1
postgres=# insert into t1 values (7);
INSERT 0 1
postgres=# insert into t1 values (8);
INSERT 0 1
postgres=# insert into t1 values (9);
INSERT 0 1
postgres=# insert into t1 values (10);
INSERT 0 1
postgres=# select xact_commit, xact_rollback from pg_stat_database where datname = 'postgres';
-[ RECORD 1 ]-+---
xact_commit | 33
xact_rollback | 0
- Subscriber
postgres=# alter subscription sub disable;
ALTER SUBSCRIPTION
- Publisher
postgres=# select xact_commit, xact_rollback from pg_stat_database where datname = 'postgres';
-[ RECORD 1 ]-+---
xact_commit | 36
xact_rollback | 10
What seems to be happening is that the amount of transactions decoded by the walsender are being added in pg_stat_database.xact_rollback. But these changes are only flushed to global stats when the walsender gets terminated.
This is causing inconsistency in monitoring TPS metric of a database where we eventually see sudden spikes of TPS in the order of millions.
Regards,
Rafael Castro.
