Disable parallel execution in snapshot

Author: knizhnik

src/backend/access/index/indexam.c

@@ -78,6 +78,7 @@
 #include "storage/bufmgr.h"
 #include "storage/lmgr.h"
 #include "storage/predicate.h"
+#include "storage/snapfs.h"
 #include "utils/snapmgr.h"
 #include "utils/tqual.h"
 
@@ -634,7 +635,7 @@ index_fetch_heap(IndexScanDesc scan)
 	 * recovery because it may violate MVCC to do so.  See comments in
 	 * RelationGetIndexScan().
 	 */
-	if (!scan->xactStartedInRecovery)
+	if (!scan->xactStartedInRecovery && !SFS_IN_SNAPSHOT())
 		scan->kill_prior_tuple = all_dead;
 
 	return NULL;

src/backend/optimizer/plan/planner.c

@@ -53,6 +53,7 @@
 #include "parser/parse_agg.h"
 #include "rewrite/rewriteManip.h"
 #include "storage/dsm_impl.h"
+#include "storage/snapfs.h"
 #include "utils/rel.h"
 #include "utils/selfuncs.h"
 #include "utils/lsyscache.h"
@@ -338,6 +339,7 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 		parse->commandType == CMD_SELECT &&
 		!parse->hasModifyingCTE &&
 		max_parallel_workers_per_gather > 0 &&
+		!SFS_IN_SNAPSHOT() &&
 		!IsParallelWorker() &&
 		!IsolationIsSerializable())
 	{