Postgresql-17 hangs waiting on LWLock in pg_stat_monitor (PortalCleanup phase)

[ayder]

Description

We are experiencing an issue where a PostgreSQL instance becomes stuck while using the pg_stat_monitor extension. A core dump shows that the backend is waiting on a lightweight lock (LWLockAcquire()) invoked within pg_stat_monitor’s pgsm_store() function. The backend never completes, causing all queries on the backend to hang indefinitely.

•	Any guidance on what might cause pgsm_store() to block in LWLockAcquire()?
•	Suggestions for debug settings, patches, or configuration changes?
•	Is this a known issue with the current version of pg_stat_monitor?

Thank you for your help!

Expected Results

The backend should not become stuck. Queries should complete, and pg_stat_monitor should not cause indefinite blocking.

Actual Results

• All backend processes is stuck, and queries hang, do not complete.
• Attaching gcore and examining the core file with gdb shows the following stack trace snippet:

#1  0x00007fa9e516af18 in __new_sem_wait_slow.constprop.0 () from /lib64/libpthread.so.0
#2  0x00000000007ce242 in PGSemaphoreLock ()
#3  0x000000000085528c in LWLockAcquire ()
#4  0x00007fa9de56e63d in pgsm_store () from /usr/pgsql-17/lib/pg_stat_monitor.so
#5  0x00007fa9de56fe1b in pgsm_ExecutorEnd () from /usr/pgsql-17/lib/pg_stat_monitor.so
#6  0x0000000000673491 in PortalCleanup ()
#7  0x00000000009cc7b4 in PortalDrop ()
#8  0x00000000008675ce in exec_simple_query ()
#9  0x0000000000868db4 in PostgresMain ()

Version

Environment:
• PostgreSQL Version: postgresql17-server-17.2-1PGDG.rhel8.x86_64
• pg_stat_monitor Version: pg_stat_monitor_17-2.1.0-1PGDG.rhel8.x86_64
• Operating System: Oracle Linux Server release 8.10 / 5.15.0-302.167.6.el8uek.x86_64
• Installation Method: RPM

Steps to reproduce

1.	Running queries under heavy busy conditions. (Many truncate and inserts)
2.	Possibly occurs after a certain procedure calls.
3.	Eventually, backend hangs during PortalCleanup() with pg_stat_monitor code in the call stack.

Relevant logs

No response

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