Hi, in the course of https://postgr.es/m/3471359.1615937770%40sss.pgh.pa.us I saw a leak in pgstat_read_statsfiles(), more precisely: /* Allocate the space for replication slot statistics */ replSlotStats = palloc0(max_replication_slots * sizeof(PgStat_ReplSlotStats));
the issue is that the current memory context is not set by pgstat_read_statsfiles(). In some cases CurrentMemoryContext is going to be a long-lived context, accumulating those allocations over time. In other contexts it will be a too short lived context, e.g. an ExprContext from the pg_stat_* invocation in the query. A reproducer for the latter: postgres[2252294][1]=# SELECT pg_create_logical_replication_slot('test', 'test_decoding'); ┌────────────────────────────────────┐ │ pg_create_logical_replication_slot │ ├────────────────────────────────────┤ │ (test,0/456C1878) │ └────────────────────────────────────┘ (1 row) postgres[2252294][1]=# BEGIN ; BEGIN postgres[2252294][1]*=# SELECT * FROM pg_stat_replication_slots ; ┌───────────┬────────────┬─────────────┬─────────────┬─────────────┬──────────────┬──────────────┬─────────────┐ │ slot_name │ spill_txns │ spill_count │ spill_bytes │ stream_txns │ stream_count │ stream_bytes │ stats_reset │ ├───────────┼────────────┼─────────────┼─────────────┼─────────────┼──────────────┼──────────────┼─────────────┤ │ test │ 0 │ 0 │ 0 │ 0 │ 0 │ 0 │ (null) │ └───────────┴────────────┴─────────────┴─────────────┴─────────────┴──────────────┴──────────────┴─────────────┘ (1 row) postgres[2252294][1]*=# SELECT * FROM pg_stat_replication_slots ; ┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────> │ > ├─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────> │ \x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F\x7F> └─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────> (1 row) I'll push the minimal fix of forcing the allocation to happen in pgStatLocalContext and setting it to NULL in pgstat_clear_snapshot(). But it seems like we just shouldn't allocate it dynamically at all? max_replication_slots doesn't change during postmaster lifetime, so it seems like it should just be allocated once? Greetings, Andres Freund