diff --git a/gpAux/gpdemo/demo_cluster.sh b/gpAux/gpdemo/demo_cluster.sh
index 73a85ade494..f1a266cfdbb 100755
--- a/gpAux/gpdemo/demo_cluster.sh
+++ b/gpAux/gpdemo/demo_cluster.sh
@@ -347,6 +347,8 @@ if [ "${ENABLE_COPY}" == "true" ]; then
 		ycmdb.yc_allow_copy_to_program=on
 		ycmdb.yc_allow_copy_from_file=on
 		ycmdb.yc_allow_copy_to_file=on
+		wal_level=hot_standby
+		hot_standby=on
 
 	EOF
 fi
diff --git a/gpcontrib/gpdebug/Makefile b/gpcontrib/gpdebug/Makefile
new file mode 100644
index 00000000000..730c487b6cf
--- /dev/null
+++ b/gpcontrib/gpdebug/Makefile
@@ -0,0 +1,12 @@
+# gpcontrib/gpdebug/Makefile
+
+MODULE_big = gpdebug
+OBJS = gpdebug.o $(WIN32RES)
+
+EXTENSION = gpdebug
+DATA = gpdebug--1.0.sql
+PGFILEDESC = "gpdebug - An debug logging for PostgreSQL"
+
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
diff --git a/gpcontrib/gpdebug/gpdebug--1.0.sql b/gpcontrib/gpdebug/gpdebug--1.0.sql
new file mode 100644
index 00000000000..0a12fa1a07e
--- /dev/null
+++ b/gpcontrib/gpdebug/gpdebug--1.0.sql
@@ -0,0 +1,2 @@
+CREATE OR REPLACE FUNCTION cleanupAllGangs() RETURNS BOOL
+AS 'MODULE_PATHNAME','cleanupAllGangs' LANGUAGE C;
diff --git a/gpcontrib/gpdebug/gpdebug.c b/gpcontrib/gpdebug/gpdebug.c
new file mode 100644
index 00000000000..6708d2b9748
--- /dev/null
+++ b/gpcontrib/gpdebug/gpdebug.c
@@ -0,0 +1,27 @@
+
+
+/*------------------------------------------------------------------------------
+ * gpdebug.c
+ *
+ * Copyright (c) 2014-2021, PostgreSQL Global Development Group
+ *------------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+
+#include "cdb/cdbvars.h"
+#include "cdb/cdbgang.h"
+
+PG_MODULE_MAGIC;
+
+void _PG_init(void);
+
+PG_FUNCTION_INFO_V1(cleanupAllGangs);
+Datum
+cleanupAllGangs(PG_FUNCTION_ARGS)
+{
+	if (Gp_role != GP_ROLE_DISPATCH)
+		elog(ERROR, "cleanupAllGangs can only be executed on master");
+	DisconnectAndDestroyAllGangs(false);
+	PG_RETURN_BOOL(true);
+}
\ No newline at end of file
diff --git a/gpcontrib/gpdebug/gpdebug.control b/gpcontrib/gpdebug/gpdebug.control
new file mode 100644
index 00000000000..3b53eeddd8c
--- /dev/null
+++ b/gpcontrib/gpdebug/gpdebug.control
@@ -0,0 +1,5 @@
+# gpdebug extension
+comment = 'provides debug functionality'
+default_version = '1.0'
+module_pathname = '$libdir/gpdebug'
+relocatable = true
diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index a0be6df4e2b..30272ae3ec1 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1879,7 +1879,7 @@ GetOldestPreparedTransaction()
 void
 StandbyRecoverPreparedTransactions(bool overwriteOK)
 {
-	elog(ERROR, "Hot Standby not supported");
+	// elog(ERROR, "Hot Standby not supported");
 }
 
 /*
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index d963e3f76d0..30b15288abe 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -2329,8 +2329,8 @@ StartTransaction(void)
 	 * hot standby is enabled.  This mode is not supported in
 	 * Greenplum yet.
 	 */
-	AssertImply(DistributedTransactionContext != DTX_CONTEXT_LOCAL_ONLY,
-				!s->startedInRecovery);
+	// AssertImply(DistributedTransactionContext != DTX_CONTEXT_LOCAL_ONLY,
+	// 			!s->startedInRecovery);
 	/*
 	 * MPP Modification
 	 *
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 8552d760b15..22930e74927 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7200,7 +7200,7 @@ StartupXLOG(void)
 				oldestActiveXID = PrescanPreparedTransactions(&xids, &nxids);
 			else
 				oldestActiveXID = checkPoint.oldestActiveXid;
-			Assert(TransactionIdIsValid(oldestActiveXID));
+			// Assert(TransactionIdIsValid(oldestActiveXID));
 
 			/* Tell procarray about the range of xids it has to deal with */
 			ProcArrayInitRecovery(ShmemVariableCache->nextXid);
diff --git a/src/backend/cdb/cdbutil.c b/src/backend/cdb/cdbutil.c
index 0127f6d20d3..f39784bcd75 100644
--- a/src/backend/cdb/cdbutil.c
+++ b/src/backend/cdb/cdbutil.c
@@ -82,6 +82,7 @@
 #endif
 
 bool gp_count_host_segments_using_address = false;
+bool gp_dispatch_on_mirrors = false;
 MemoryContext CdbComponentsContext = NULL;
 static CdbComponentDatabases *cdb_component_dbs = NULL;
 
@@ -92,6 +93,7 @@ static CdbComponentDatabases *getCdbComponentInfo(void);
 static void cleanupComponentIdleQEs(CdbComponentDatabaseInfo *cdi, bool includeWriter);
 
 static int	CdbComponentDatabaseInfoCompare(const void *p1, const void *p2);
+static int	CdbComponentDatabaseInfoComparem(const void *p1, const void *p2);
 
 static GpSegConfigEntry * readGpSegConfigFromCatalog(int *total_dbs);
 static GpSegConfigEntry * readGpSegConfigFromFTSFiles(int *total_dbs);
@@ -439,10 +441,20 @@ getCdbComponentInfo(void)
 		pRow->numIdleQEs = 0;
 		pRow->numActiveQEs = 0;
 
-		if (config->role != GP_SEGMENT_CONFIGURATION_ROLE_PRIMARY ||
-			(gp_count_host_segments_using_address &&
-			 (config->hostip == NULL || strlen(config->hostip) == 0)))
-			continue;
+		if (gp_dispatch_on_mirrors)
+		{
+			if (config->role != GP_SEGMENT_CONFIGURATION_ROLE_MIRROR ||
+				(gp_count_host_segments_using_address &&
+				(config->hostip == NULL || strlen(config->hostip) == 0)))
+				continue;
+		}
+		else
+		{
+			if (config->role != GP_SEGMENT_CONFIGURATION_ROLE_PRIMARY ||
+				(gp_count_host_segments_using_address &&
+				(config->hostip == NULL || strlen(config->hostip) == 0)))
+				continue;
+		}
 
 		hsEntry = (HostSegsEntry *) hash_search(hostSegsHash,
 												gp_count_host_segments_using_address ? config->hostip : config->hostname,
@@ -474,14 +486,26 @@ getCdbComponentInfo(void)
 	/*
 	 * Now sort the data by segindex, isprimary desc
 	 */
-	qsort(component_databases->segment_db_info,
-		  component_databases->total_segment_dbs, sizeof(CdbComponentDatabaseInfo),
-		  CdbComponentDatabaseInfoCompare);
+	if (gp_dispatch_on_mirrors)
+	{
+		qsort(component_databases->segment_db_info,
+			component_databases->total_segment_dbs, sizeof(CdbComponentDatabaseInfo),
+			CdbComponentDatabaseInfoComparem);
 
-	qsort(component_databases->entry_db_info,
-		  component_databases->total_entry_dbs, sizeof(CdbComponentDatabaseInfo),
-		  CdbComponentDatabaseInfoCompare);
+		qsort(component_databases->entry_db_info,
+			component_databases->total_entry_dbs, sizeof(CdbComponentDatabaseInfo),
+			CdbComponentDatabaseInfoComparem);
+	}
+	else 
+	{
+		qsort(component_databases->segment_db_info,
+			component_databases->total_segment_dbs, sizeof(CdbComponentDatabaseInfo),
+			CdbComponentDatabaseInfoCompare);
 
+		qsort(component_databases->entry_db_info,
+			component_databases->total_entry_dbs, sizeof(CdbComponentDatabaseInfo),
+			CdbComponentDatabaseInfoCompare);
+	}
 	/*
 	 * Now count the number of distinct segindexes. Since it's sorted, this is
 	 * easy.
@@ -558,10 +582,20 @@ getCdbComponentInfo(void)
 	{
 		cdbInfo = &component_databases->segment_db_info[i];
 
-		if (cdbInfo->config->role != GP_SEGMENT_CONFIGURATION_ROLE_PRIMARY ||
-			(gp_count_host_segments_using_address &&
-			 (cdbInfo->config->hostip == NULL || strlen(cdbInfo->config->hostip) == 0)))
-			continue;
+		if (gp_dispatch_on_mirrors)
+		{
+			if (cdbInfo->config->role != GP_SEGMENT_CONFIGURATION_ROLE_MIRROR ||
+				(gp_count_host_segments_using_address &&
+				(cdbInfo->config->hostip == NULL || strlen(cdbInfo->config->hostip) == 0)))
+				continue;
+		}
+		else
+		{
+			if (cdbInfo->config->role != GP_SEGMENT_CONFIGURATION_ROLE_PRIMARY ||
+				(gp_count_host_segments_using_address &&
+				(cdbInfo->config->hostip == NULL || strlen(cdbInfo->config->hostip) == 0)))
+				continue;
+		}
 
 		hsEntry = (HostSegsEntry *) hash_search(hostSegsHash,
 												gp_count_host_segments_using_address ? cdbInfo->config->hostip : cdbInfo->config->hostname,
@@ -575,10 +609,20 @@ getCdbComponentInfo(void)
 	{
 		cdbInfo = &component_databases->entry_db_info[i];
 
-		if (cdbInfo->config->role != GP_SEGMENT_CONFIGURATION_ROLE_PRIMARY ||
-			(gp_count_host_segments_using_address &&
-			 (cdbInfo->config->hostip == NULL || strlen(cdbInfo->config->hostip) == 0)))
-			continue;
+		if (gp_dispatch_on_mirrors)
+		{
+			if (cdbInfo->config->role != GP_SEGMENT_CONFIGURATION_ROLE_MIRROR ||
+				(gp_count_host_segments_using_address &&
+				(cdbInfo->config->hostip == NULL || strlen(cdbInfo->config->hostip) == 0)))
+				continue;
+		}
+		else
+		{
+			if (cdbInfo->config->role != GP_SEGMENT_CONFIGURATION_ROLE_PRIMARY ||
+				(gp_count_host_segments_using_address &&
+				(cdbInfo->config->hostip == NULL || strlen(cdbInfo->config->hostip) == 0)))
+				continue;
+		}
 
 		hsEntry = (HostSegsEntry *) hash_search(hostSegsHash,
 												gp_count_host_segments_using_address ? cdbInfo->config->hostip : cdbInfo->config->hostname,
@@ -847,7 +891,9 @@ cdbcomponent_allocateIdleQE(int contentId, SegmentType segmentType)
 		 * 1. for entrydb, it's never be writer.
 		 * 2. for first QE, it must be a writer.
 		 */
+		/*XXX: what if gp_dispatch_on_mirrors?*/
 		isWriter = contentId == -1 ? false: (cdbinfo->numIdleQEs == 0 && cdbinfo->numActiveQEs == 0);
+		
 		segdbDesc = cdbconn_createSegmentDescriptor(cdbinfo, nextQEIdentifer(cdbinfo->cdbs), isWriter);
 	}
 
@@ -1041,11 +1087,20 @@ cdbcomponent_getComponentInfo(int contentId)
 		Assert(cdbs->total_segment_dbs == cdbs->total_segments * 2);
 		cdbInfo = &cdbs->segment_db_info[2 * contentId];
 
-		if (!SEGMENT_IS_ACTIVE_PRIMARY(cdbInfo))
+		if (gp_dispatch_on_mirrors)
 		{
-			cdbInfo = &cdbs->segment_db_info[2 * contentId + 1];
+			if (!SEGMENT_IS_ACTIVE_MIRROR(cdbInfo))
+			{
+				cdbInfo = &cdbs->segment_db_info[2 * contentId + 1];
+			}
+		}
+		else 
+		{
+			if (!SEGMENT_IS_ACTIVE_PRIMARY(cdbInfo))
+			{
+				cdbInfo = &cdbs->segment_db_info[2 * contentId + 1];
+			}
 		}
-
 		return cdbInfo;
 	}
 
@@ -1228,6 +1283,31 @@ CdbComponentDatabaseInfoCompare(const void *p1, const void *p2)
 	return cmp;
 }
 
+static int
+CdbComponentDatabaseInfoComparem(const void *p1, const void *p2)
+{
+	const CdbComponentDatabaseInfo *obj1 = (CdbComponentDatabaseInfo *) p1;
+	const CdbComponentDatabaseInfo *obj2 = (CdbComponentDatabaseInfo *) p2;
+
+	int			cmp = obj1->config->segindex - obj2->config->segindex;
+
+	if (cmp == 0)
+	{
+		int			obj2cmp = 0;
+		int			obj1cmp = 0;
+
+		if (SEGMENT_IS_ACTIVE_MIRROR(obj2))
+			obj2cmp = 1;
+
+		if (SEGMENT_IS_ACTIVE_MIRROR(obj1))
+			obj1cmp = 1;
+
+		cmp = obj2cmp - obj1cmp;
+	}
+
+	return cmp;
+}
+
 /*
  * Maintain a cache of names.
  *
diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
index 8fa73b6236f..a523fa7cf64 100644
--- a/src/backend/storage/lmgr/lock.c
+++ b/src/backend/storage/lmgr/lock.c
@@ -36,6 +36,7 @@
 #include "access/twophase.h"
 #include "access/twophase_rmgr.h"
 #include "cdb/cdbvars.h"
+#include "cdb/cdbutil.h"
 #include "miscadmin.h"
 #include "pg_trace.h"
 #include "pgstat.h"
@@ -837,7 +838,7 @@ LockAcquireExtended(const LOCKTAG *locktag,
 	
 	if (lockmethodid == DEFAULT_LOCKMETHOD && locktag->locktag_type != LOCKTAG_TRANSACTION)
 	{
-		if (Gp_role == GP_ROLE_EXECUTE && !Gp_is_writer)
+		if (Gp_role == GP_ROLE_EXECUTE && !Gp_is_writer && !gp_dispatch_on_mirrors)
 		{	
 			if (lockHolderProcPtr == NULL || lockHolderProcPtr == MyProc)
 			{
@@ -857,7 +858,7 @@ LockAcquireExtended(const LOCKTAG *locktag,
 					lockHolderProcPtr = proc;
 				}
 				else
-					ereport(FATAL,
+					ereport(WARNING,
 							(errcode(ERRCODE_GP_INTERCONNECTION_ERROR),
 							 errmsg(WRITER_IS_MISSING_MSG),
 							 errdetail("lock [%u,%u] %s %d. "
diff --git a/src/backend/utils/misc/guc_gp.c b/src/backend/utils/misc/guc_gp.c
index 1e85c1ff255..da02c8b5b37 100644
--- a/src/backend/utils/misc/guc_gp.c
+++ b/src/backend/utils/misc/guc_gp.c
@@ -3197,7 +3197,13 @@ struct config_bool ConfigureNamesBool_gp[] =
 		&gp_use_fastanalyze,
 		false, NULL, NULL
 	},
-
+	{
+		{"gp_dispatch_on_mirrors", PGC_USERSET, RESOURCES,
+		},
+		&gp_dispatch_on_mirrors,
+		false, NULL, NULL
+	},
+	
 	{
 		{"stats_queue_level", PGC_SUSET, STATS_COLLECTOR,
 			gettext_noop("Collects resource queue-level statistics on database activity."),
diff --git a/src/include/cdb/cdbutil.h b/src/include/cdb/cdbutil.h
index 17570586fdb..236a2b6c5ef 100644
--- a/src/include/cdb/cdbutil.h
+++ b/src/include/cdb/cdbutil.h
@@ -206,6 +206,7 @@ extern int16 contentid_get_dbid(int16 contentid, char role, bool getPreferredRol
 extern int numsegmentsFromQD;
 
 extern bool gp_count_host_segments_using_address;
+extern bool gp_dispatch_on_mirrors;
 
 /*
  * Returns the number of segments
diff --git a/src/include/utils/unsync_guc_name.h b/src/include/utils/unsync_guc_name.h
index 45adb3a496f..5ecc02ad167 100644
--- a/src/include/utils/unsync_guc_name.h
+++ b/src/include/utils/unsync_guc_name.h
@@ -160,6 +160,7 @@
 		"gp_dispatch_keepalives_idle",
 		"gp_dispatch_keepalives_interval",
 		"gp_dispatch_keepalives_count",
+		"gp_dispatch_on_mirrors",
 		"gp_distinct_grouping_sets_threshold",
 		"gp_dtx_recovery_interval",
 		"gp_dtx_recovery_prepared_period",