Call FlushDistTableCache() before stats collection.

src/backend/distributed/utils/maintenanced.c

@@ -318,6 +318,7 @@ CitusMaintenanceDaemonMain(Datum main_arg)
 			}
 			else if (CheckCitusVersion(DEBUG1) && CitusHasBeenLoaded())
 			{
+				FlushDistTableCache();
 				WarnIfSyncDNS();
 				statsCollectionSuccess = CollectBasicUsageStatistics();
 			}

src/backend/distributed/utils/metadata_cache.c

@@ -177,6 +177,7 @@ static void RegisterWorkerNodeCacheCallbacks(void);
 static void RegisterLocalGroupIdCacheCallbacks(void);
 static uint32 WorkerNodeHashCode(const void *key, Size keySize);
 static void ResetDistTableCacheEntry(DistTableCacheEntry *cacheEntry);
+static void CreateDistTableCache(void);
 static void InvalidateDistRelationCacheCallback(Datum argument, Oid relationId);
 static void InvalidateNodeRelationCacheCallback(Datum argument, Oid relationId);
 static void InvalidateLocalGroupIdRelationCacheCallback(Datum argument, Oid relationId);
@@ -2345,13 +2346,7 @@ InitializeDistTableCache(void)
 	DistShardScanKey[0].sk_attno = Anum_pg_dist_shard_logicalrelid;
 
 	/* initialize the per-table hash table */
-	MemSet(&info, 0, sizeof(info));
+	CreateDistTableCache();
-	info.keysize = sizeof(Oid);
-	info.entrysize = sizeof(DistTableCacheEntry);
-	info.hash = tag_hash;
-	DistTableCacheHash =
-		hash_create("Distributed Relation Cache", 32, &info,
-					HASH_ELEM | HASH_FUNCTION);
 
 	/* initialize the per-shard hash table */
 	MemSet(&info, 0, sizeof(info));
@@ -2731,6 +2726,43 @@ InvalidateDistRelationCacheCallback(Datum argument, Oid relationId)
 }
 
 
+/*
+ * FlushDistTableCache flushes the entire distributed relation cache, frees
+ * all entries, and recreates the cache.
+ */
+void
+FlushDistTableCache(void)
+{
+	DistTableCacheEntry *cacheEntry = NULL;
+	HASH_SEQ_STATUS status;
+
+	hash_seq_init(&status, DistTableCacheHash);
+
+	while ((cacheEntry = (DistTableCacheEntry *) hash_seq_search(&status)) != NULL)
+	{
+		ResetDistTableCacheEntry(cacheEntry);
+	}
+
+	hash_destroy(DistTableCacheHash);
+	CreateDistTableCache();
+}
+
+
+/* CreateDistTableCache initializes the per-table hash table */
+static void
+CreateDistTableCache(void)
+{
+	HASHCTL info;
+	MemSet(&info, 0, sizeof(info));
+	info.keysize = sizeof(Oid);
+	info.entrysize = sizeof(DistTableCacheEntry);
+	info.hash = tag_hash;
+	DistTableCacheHash =
+		hash_create("Distributed Relation Cache", 32, &info,
+					HASH_ELEM | HASH_FUNCTION);
+}
+
+
 /*
  * InvalidateMetadataSystemCache resets all the cached OIDs and the extensionLoaded flag,
  * and invalidates the worker node and local group ID caches.

src/include/distributed/metadata_cache.h

@@ -86,6 +86,7 @@ extern List * DistTableOidList(void);
 extern List * ShardPlacementList(uint64 shardId);
 extern void CitusInvalidateRelcacheByRelid(Oid relationId);
 extern void CitusInvalidateRelcacheByShardId(int64 shardId);
+extern void FlushDistTableCache(void);
 extern void InvalidateMetadataSystemCache(void);
 extern Datum DistNodeMetadata(void);