From: Tatsuo Ishii <ishii@sraoss.co.jp>
Date: Tue, 2 Apr 2024 10:30:27 +0000 (+0900)
Subject: Fix errors/hung up when load_balance_mode is off.
X-Git-Tag: V4_6_0_BETA1~105
X-Git-Url: http://git.postgresql.org/gitweb/static/help.php?a=commitdiff_plain;h=da2b555e75444b50a949f181dbfeeabb3bc0a076;p=pgpool2.git

Fix errors/hung up when load_balance_mode is off.

Commit: 3f3c1656 Fix statement_level_load_balance with BEGIN etc.

brought errors/hung up when load_balance_mode is off, primary node id
is not 0 and queries are BEGIN etc.

pool_setall_node_to_be_sent() checked if the node is primary. If not,
just returned with empty where_to_send map which makes
set_vrtual_main_node() not to set
query_context->virtual_main_node_id. As a result, MAIN_NODE macro
(it's actually pool_virtual_main_db_node_id()) returns
REAL_MAIN_NODE_ID, which is 0 if node 0 is alive (this should have
been primary node id).

Following simple test reveals the bug.

(1) create a two-node cluster using pgpool_setup

(2) shutdown node 0 and recover node 1 (pcp_recovery_node 0). This
makes node 0 to be standby, node 1 to be primary.

(3) add followings to pgpool.conf and restart whole cluster.

load_balance_mode = off
backend_weight1 = 0

(4) type "begin" from psql. It gets stuck.

Bug found and analyzed by Emond Papegaaij.
Discussion: https://www.pgpool.net/pipermail/pgpool-general/2024-March/009113.html
Backpatch-through: v4.1
---

diff --git a/src/context/pool_query_context.c b/src/context/pool_query_context.c
index 3381fb42a..eea355425 100644
--- a/src/context/pool_query_context.c
+++ b/src/context/pool_query_context.c
@@ -244,20 +244,23 @@ pool_setall_node_to_be_sent(POOL_QUERY_CONTEXT * query_context)
 			{
 				/*
 				 * If load balance mode is disabled, only send to the primary node.
-				 * or send to the main node if primary node does not exist.
+				 * If primary node does not exist, send to the main node.
 				 */
 				if (!pool_config->load_balance_mode)
 				{
 					if (i == PRIMARY_NODE_ID ||
 						(PRIMARY_NODE_ID < 0 && MAIN_NODE_ID == i))
+					{
 						query_context->where_to_send[i] = true;
-					break;
+						break;
+					}
+					continue;
 				}
 				else
 					/*
 					 * If the node is not primary node nor load balance node,
-					 * there's no point to send query except statement load
-					 * balance is enabled.
+					 * there's no point to send query except statement level
+					 * load balance is enabled.
 					 */
 					if (!pool_config->statement_level_load_balance &&
 						i != PRIMARY_NODE_ID && i != sc->load_balance_node_id)