postgres
diff --git a/‎src/backend/utils/activity/pgstat_shmem.c
Lines changed: 35 additions & 5 deletions b/‎src/backend/utils/activity/pgstat_shmem.c
Lines changed: 35 additions & 5 deletions
diff --git a/‎src/include/utils/pgstat_internal.h
Lines changed: 19 additions & 0 deletions b/‎src/include/utils/pgstat_internal.h
Lines changed: 19 additions & 0 deletions
@@ -304,6 +304,11 @@ pgstat_init_entry(PgStat_Kind kind,
 	 * further if a longer lived reference is needed.
 	 */
 	pg_atomic_init_u32(&shhashent->refcount, 1);
+
+	/*
+	 * Initialize "generation" to 0, as freshly created.
+	 */
+	pg_atomic_init_u32(&shhashent->generation, 0);
 	shhashent->dropped = false;
 
 	chunk = dsa_allocate0(pgStatLocal.dsa, pgstat_get_kind_info(kind)->shared_size);
@@ -327,6 +332,12 @@ pgstat_reinit_entry(PgStat_Kind kind, PgStatShared_HashEntry *shhashent)
 
 	/* mark as not dropped anymore */
 	pg_atomic_fetch_add_u32(&shhashent->refcount, 1);
+
+	/*
+	 * Increment "generation", to let any backend with local references know
+	 * that what they point to is outdated.
+	 */
+	pg_atomic_fetch_add_u32(&shhashent->generation, 1);
 	shhashent->dropped = false;
 
 	/* reinitialize content */
@@ -367,6 +378,7 @@ pgstat_acquire_entry_ref(PgStat_EntryRef *entry_ref,
 
 	entry_ref->shared_stats = shheader;
 	entry_ref->shared_entry = shhashent;
+	entry_ref->generation = pg_atomic_read_u32(&shhashent->generation);
 }
 
 /*
@@ -532,7 +544,8 @@ pgstat_get_entry_ref(PgStat_Kind kind, Oid dboid, uint64 objid, bool create,
 			 * case are replication slot stats, where a new slot can be
 			 * created with the same index just after dropping. But oid
 			 * wraparound can lead to other cases as well. We just reset the
-			 * stats to their plain state.
+			 * stats to their plain state, while incrementing its "generation"
+			 * in the shared entry for any remaining local references.
 			 */
 			shheader = pgstat_reinit_entry(kind, shhashent);
 			pgstat_acquire_entry_ref(entry_ref, shhashent, shheader);
@@ -599,10 +612,27 @@ pgstat_release_entry_ref(PgStat_HashKey key, PgStat_EntryRef *entry_ref,
 			if (!shent)
 				elog(ERROR, "could not find just referenced shared stats entry");
 
-			Assert(pg_atomic_read_u32(&entry_ref->shared_entry->refcount) == 0);
-			Assert(entry_ref->shared_entry == shent);
-
-			pgstat_free_entry(shent, NULL);
+			/*
+			 * This entry may have been reinitialized while trying to release
+			 * it, so double-check that it has not been reused while holding a
+			 * lock on its shared entry.
+			 */
+			if (pg_atomic_read_u32(&entry_ref->shared_entry->generation) ==
+				entry_ref->generation)
+			{
+				/* Same "generation", so we're OK with the removal */
+				Assert(pg_atomic_read_u32(&entry_ref->shared_entry->refcount) == 0);
+				Assert(entry_ref->shared_entry == shent);
+				pgstat_free_entry(shent, NULL);
+			}
+			else
+			{
+				/*
+				 * Shared stats entry has been reinitialized, so do not drop
+				 * its shared entry, only release its lock.
+				 */
+				dshash_release_lock(pgStatLocal.shared_hash, shent);
+			}
 		}
 	}
 
 
@@ -94,6 +94,19 @@ typedef struct PgStatShared_HashEntry
 	 */
 	pg_atomic_uint32 refcount;
 
+	/*
+	 * Counter tracking the number of times the entry has been reused.
+	 *
+	 * Set to 0 when the entry is created, and incremented by one each time
+	 * the shared entry is reinitialized with pgstat_reinit_entry().
+	 *
+	 * May only be incremented / decremented while holding at least a shared
+	 * lock on the dshash partition containing the entry. Like refcount, it
+	 * needs to be an atomic variable because multiple backends can increment
+	 * the generation with just a shared lock.
+	 */
+	pg_atomic_uint32 generation;
+
 	/*
 	 * Pointer to shared stats. The stats entry always starts with
 	 * PgStatShared_Common, embedded in a larger struct containing the
@@ -133,6 +146,12 @@ typedef struct PgStat_EntryRef
 	 */
 	PgStatShared_Common *shared_stats;
 
+	/*
+	 * Copy of PgStatShared_HashEntry->generation, keeping locally track of
+	 * the shared stats entry "generation" retrieved (number of times reused).
+	 */
+	uint32		generation;
+
 	/*
 	 * Pending statistics data that will need to be flushed to shared memory
 	 * stats eventually. Each stats kind utilizing pending data defines what