diff --git a/dbcon/joblist/distributedenginecomm.cpp b/dbcon/joblist/distributedenginecomm.cpp
index b250c1c66..649bbe006 100644
--- a/dbcon/joblist/distributedenginecomm.cpp
+++ b/dbcon/joblist/distributedenginecomm.cpp
@@ -1,5 +1,5 @@
 /* Copyright (C) 2014 InfiniDB, Inc.
- * Copyright (C) 2016-2020 MariaDB Corporation.
+ * Copyright (C) 2016-2022 MariaDB Corporation.
 
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License
@@ -749,7 +749,7 @@ void DistributedEngineComm::sendAcks(uint32_t uniqueID, const vector<SBS>& msgs,
     {
       uint64_t totalUnackedWork = 0;
 
-      for (uint32_t i = 0; i < pmCount; i++)
+      for (int i = pmCount - 1; i >= 0; --i)
         totalUnackedWork += mqe->unackedWork[i];
 
       if (totalUnackedWork == 0)
@@ -769,7 +769,6 @@ void DistributedEngineComm::sendAcks(uint32_t uniqueID, const vector<SBS>& msgs,
 void DistributedEngineComm::nextPMToACK(boost::shared_ptr<MQE> mqe, uint32_t maxAck, uint32_t* sockIndex,
                                         uint16_t* numToAck)
 {
-  uint32_t i;
   uint32_t& nextIndex = mqe->ackSocketIndex;
 
   /* Other threads can be touching mqe->unackedWork at the same time, but because of
@@ -790,7 +789,7 @@ void DistributedEngineComm::nextPMToACK(boost::shared_ptr<MQE> mqe, uint32_t max
   }
   else
   {
-    for (i = 0; i < pmCount; i++)
+    for (int i = pmCount - 1; i >= 0; --i)
     {
       uint32_t curVal = mqe->unackedWork[nextIndex];
       uint32_t unackedWork = (curVal > maxAck ? maxAck : curVal);
@@ -812,8 +811,7 @@ void DistributedEngineComm::nextPMToACK(boost::shared_ptr<MQE> mqe, uint32_t max
     }
 
     cerr << "DEC::nextPMToACK(): Couldn't find a PM to ACK! ";
-
-    for (i = 0; i < pmCount; i++)
+    for (int i = pmCount - 1; i >= 0; --i)
       cerr << mqe->unackedWork[i] << " ";
 
     cerr << " max: " << maxAck;
@@ -1051,6 +1049,9 @@ void DistributedEngineComm::pushToTheLocalQueueAndNotifyRecv(const messageqcpp::
   inMemoryEM2PPExchCV_.notify_one();
 }
 
+// This routine has an unexpected side-effect on its argument's SBS, namely
+// SBS is cleared when it is sent to PP at the same host. This fact forces any
+// code uses ::writeToClient to send to a local node in the last turn.
 int DistributedEngineComm::writeToClient(size_t aPMIndex, const SBS& bs, uint32_t senderUniqueID,
                                          bool doInterleaving)
 {
diff --git a/mysql-test/columnstore/multinode/mcol-5279.result b/mysql-test/columnstore/multinode/mcol-5279.result
new file mode 100644
index 000000000..fb5c3b682
--- /dev/null
+++ b/mysql-test/columnstore/multinode/mcol-5279.result
@@ -0,0 +1,10 @@
+DROP DATABASE IF EXISTS mcol_5279;
+CREATE DATABASE mcol_5279;
+USE mcol_5279;
+CREATE TABLE `dd`( `acct_sk` INT(11) UNSIGNED NOT NULL, `acct_id` VARCHAR(128) NOT NULL DEFAULT 'None', `db_source_sk` INT(11) UNSIGNED NOT NULL) ENGINE=Columnstore DEFAULT CHARSET=utf8mb4;
+CREATE TABLE `ff` ( `db_source_sk` INT(11) UNSIGNED NOT NULL, `acct_id` VARCHAR(128) NOT NULL DEFAULT 'None', `acct_sk` INT(11) UNSIGNED NOT NULL DEFAULT 0 ) ENGINE=Columnstore DEFAULT CHARSET=utf8mb4;
+INSERT INTO dd SELECT ROUND(RAND() * 10, 2), substring(MD5(RAND()),1,1), ROUND(RAND() * 100, 2) FROM seq_1_to_300000;
+INSERT INTO ff SELECT ROUND(RAND() * 10, 2), substring(MD5(RAND()),1,1), ROUND(RAND() * 100, 2) FROM seq_1_to_300000;
+SELECT * FROM (SELECT ff.acct_id, COUNT(1) FROM ff JOIN dd  ON ff.acct_sk =dd.acct_sk AND ff.db_source_sk =dd.db_source_sk GROUP BY ff.acct_id LIMIT 10)s LIMIT 0;
+acct_id	COUNT(1)
+DROP DATABASE mcol_5279;
diff --git a/mysql-test/columnstore/multinode/mcol-5279.test b/mysql-test/columnstore/multinode/mcol-5279.test
new file mode 100644
index 000000000..1a10b2cb7
--- /dev/null
+++ b/mysql-test/columnstore/multinode/mcol-5279.test
@@ -0,0 +1,25 @@
+#
+# Test based on Jira MCOL-5279
+# Author: Roman Nozdrin roman.nozdrin@mariadb.com
+#
+-- source ../include/have_columnstore.inc
+
+--disable_warnings
+DROP DATABASE IF EXISTS mcol_5279;
+--enable_warnings
+
+CREATE DATABASE mcol_5279;
+USE mcol_5279;
+
+# This test makes sense when run on a multi-node cluster.
+CREATE TABLE `dd`( `acct_sk` INT(11) UNSIGNED NOT NULL, `acct_id` VARCHAR(128) NOT NULL DEFAULT 'None', `db_source_sk` INT(11) UNSIGNED NOT NULL) ENGINE=Columnstore DEFAULT CHARSET=utf8mb4;
+CREATE TABLE `ff` ( `db_source_sk` INT(11) UNSIGNED NOT NULL, `acct_id` VARCHAR(128) NOT NULL DEFAULT 'None', `acct_sk` INT(11) UNSIGNED NOT NULL DEFAULT 0 ) ENGINE=Columnstore DEFAULT CHARSET=utf8mb4;
+
+INSERT INTO dd SELECT ROUND(RAND() * 10, 2), substring(MD5(RAND()),1,1), ROUND(RAND() * 100, 2) FROM seq_1_to_300000;
+INSERT INTO ff SELECT ROUND(RAND() * 10, 2), substring(MD5(RAND()),1,1), ROUND(RAND() * 100, 2) FROM seq_1_to_300000;
+
+# The purpose is to run the statement that doesn't hang.
+SELECT * FROM (SELECT ff.acct_id, COUNT(1) FROM ff JOIN dd  ON ff.acct_sk =dd.acct_sk AND ff.db_source_sk =dd.db_source_sk GROUP BY ff.acct_id LIMIT 10)s LIMIT 0;
+
+# Clean UP
+DROP DATABASE mcol_5279;