From bdc89983d9302ab47b94925ac9fe1f5888aeaaa1 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <bossartn@amazon.com>
Date: Wed, 19 Dec 2018 01:17:25 +0000
Subject: [PATCH v1 1/4] Do not process any relations if the catalog query
 returns no results.

---
 src/bin/scripts/vacuumdb.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/bin/scripts/vacuumdb.c b/src/bin/scripts/vacuumdb.c
index bcea9e556d..886895ed2f 100644
--- a/src/bin/scripts/vacuumdb.c
+++ b/src/bin/scripts/vacuumdb.c
@@ -378,8 +378,6 @@ vacuum_one_database(const char *dbname, vacuumingOptions *vacopts,
 		fflush(stdout);
 	}
 
-	initPQExpBuffer(&sql);
-
 	/*
 	 * If a table list is not provided and we're using multiple connections,
 	 * prepare the list of tables by querying the catalogs.
@@ -390,8 +388,6 @@ vacuum_one_database(const char *dbname, vacuumingOptions *vacopts,
 		PGresult   *res;
 		int			ntups;
 
-		initPQExpBuffer(&buf);
-
 		res = executeQuery(conn,
 						   "SELECT c.relname, ns.nspname"
 						   " FROM pg_class c, pg_namespace ns\n"
@@ -403,6 +399,14 @@ vacuum_one_database(const char *dbname, vacuumingOptions *vacopts,
 						   progname, echo);
 
 		ntups = PQntuples(res);
+		if (ntups == 0)
+		{
+			PQclear(res);
+			PQfinish(conn);
+			return;
+		}
+
+		initPQExpBuffer(&buf);
 		for (i = 0; i < ntups; i++)
 		{
 			appendPQExpBufferStr(&buf,
@@ -461,6 +465,8 @@ vacuum_one_database(const char *dbname, vacuumingOptions *vacopts,
 						   stage_commands[stage], progname, echo);
 	}
 
+	initPQExpBuffer(&sql);
+
 	cell = tables ? tables->head : NULL;
 	do
 	{
-- 
2.16.5