Re: BF mamba failure

[Alexander Lakhin]

Hi,

18.03.2023 07:26, Tom Lane wrote:
Amit Kapila<amit.kapil...@gmail.com>  writes:
Peter Smith has recently reported a BF failure [1]. AFAICS, the call
stack of failure [2] is as follows:
Note the assertion report a few lines further up:
TRAP: failed Assert("pg_atomic_read_u32(&entry_ref->shared_entry->refcount) == 0"), File: 
"pgstat_shmem.c", Line: 560, PID: 25004

This assertion failure can be reproduced easily with the attached patch:
============== running regression test queries        ==============
test oldest_xmin                  ... ok           55 ms
test oldest_xmin                  ... FAILED (test process exited with exit 
code 1)      107 ms
test oldest_xmin                  ... FAILED (test process exited with exit 
code 1)        8 ms
============== shutting down postmaster               ==============

contrib/test_decoding/output_iso/log/postmaster.log contains:
TRAP: failed Assert("pg_atomic_read_u32(&entry_ref->shared_entry->refcount) == 0"), File: "pgstat_shmem.c", Line: 561, 
PID: 456844

With the sleep placed above Assert(entry_ref->shared_entry->dropped) this 
Assert fails too.

Best regards,
Alexanderdiff --git a/contrib/test_decoding/Makefile b/contrib/test_decoding/Makefile
index c7ce603706..9b3389a90e 100644
--- a/contrib/test_decoding/Makefile
+++ b/contrib/test_decoding/Makefile
@@ -9,6 +9,7 @@ REGRESS = ddl xact rewrite toast permissions decoding_in_xact \
 ISOLATION = mxact delayed_startup ondisk_startup concurrent_ddl_dml \
 	oldest_xmin snapshot_transfer subxact_without_top concurrent_stream \
 	twophase_snapshot slot_creation_error catalog_change_snapshot
+ISOLATION = oldest_xmin oldest_xmin oldest_xmin
 
 REGRESS_OPTS = --temp-config $(top_srcdir)/contrib/test_decoding/logical.conf
 ISOLATION_OPTS = --temp-config $(top_srcdir)/contrib/test_decoding/logical.conf
diff --git a/src/backend/utils/activity/pgstat_shmem.c b/src/backend/utils/activity/pgstat_shmem.c
index 09fffd0e82..5307116670 100644
--- a/src/backend/utils/activity/pgstat_shmem.c
+++ b/src/backend/utils/activity/pgstat_shmem.c
@@ -551,6 +551,7 @@ pgstat_release_entry_ref(PgStat_HashKey key, PgStat_EntryRef *entry_ref,
 			/* only dropped entries can reach a 0 refcount */
 			Assert(entry_ref->shared_entry->dropped);
 
+pg_usleep(100000L);
 			shent = dshash_find(pgStatLocal.shared_hash,
 								&entry_ref->shared_entry->key,
 								true);