Dispatch read-only query on read-only targets

Author: reshke

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

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");
 }
 
 /*

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);

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,
@@ -693,6 +737,9 @@ cdbcomponent_updateCdbComponents(void)
 
 	PG_TRY();
 	{
+		if (gp_dispatch_on_mirrors) {
+			cdb_component_dbs = NULL;
+		}
 		if (cdb_component_dbs == NULL)
 		{
 			cdb_component_dbs = getCdbComponentInfo();
@@ -742,7 +789,7 @@ cdbcomponent_getCdbComponents()
 {
 	PG_TRY();
 	{
-		if (cdb_component_dbs == NULL)
+		if (cdb_component_dbs == NULL || gp_dispatch_on_mirrors)
 		{
 			cdb_component_dbs = getCdbComponentInfo();
 			cdb_component_dbs->fts_version = getFtsVersion();
@@ -847,7 +894,9 @@ 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 +1090,20 @@ 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 +1286,31 @@ 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.
  *

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. "

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."),

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

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",