Merge pull request #4769 from citusdata/fix-4675

Populate DATABASEOID cache before CREATE INDEX CONCURRENTLY

src/backend/distributed/commands/utility_hook.c

@@ -910,6 +910,19 @@ ExecuteDistributedDDLJob(DDLJob *ddlJob)
 		 */
 		if (ddlJob->startNewTransaction)
 		{
+			/*
+			 * If cache is not populated, system catalog lookups will cause
+			 * the xmin of current backend to change. Then the last phase
+			 * of CREATE INDEX CONCURRENTLY, which is in a separate backend,
+			 * will hang waiting for our backend and result in a deadlock.
+			 *
+			 * We populate the cache before starting the next transaction to
+			 * avoid this. Most of the metadata has already been resolved in
+			 * planning phase, we only need to lookup metadata needed for
+			 * connection establishment.
+			 */
+			(void) CurrentDatabaseName();
+
 			CommitTransactionCommand();
 			StartTransactionCommand();
 		}