Fix always rebuild gang when cdbdisp_dispatchCommandInternal.

In this commit, we will only rebuild gang only when there is catalog
updation. In this way, we will imporve qps obviously in concurrence
stress testing.

Authored-by: Zhang Wenchao zwcpostgres@gmail.com

Author: zhangwenchao-123

src/backend/access/heap/heapam.c

@@ -2319,7 +2319,10 @@ heap_insert(Relation relation, HeapTuple tup, CommandId cid,
 	 * buffer.
 	 */
 	if (IsSystemRelation(relation))
+	{
+		system_relation_modified = true;
 		CacheInvalidateHeapTuple(relation, heaptup, NULL);
+	}
 
 	/* Note: speculative insertions are counted too, even if aborted later */
 	pgstat_count_heap_insert(relation, 1);
@@ -2719,6 +2722,7 @@ heap_multi_insert(Relation relation, TupleTableSlot **slots, int ntuples,
 	 */
 	if (IsCatalogRelation(relation))
 	{
+		system_relation_modified = true;
 		for (i = 0; i < ntuples; i++)
 			CacheInvalidateHeapTuple(relation, heaptuples[i], NULL);
 	}
@@ -3203,6 +3207,11 @@ heap_delete(Relation relation, ItemPointer tid,
 	 */
 	CacheInvalidateHeapTuple(relation, &tp, NULL);
 
+	if (IsCatalogRelation(relation))
+	{
+		system_relation_modified = true;
+	}
+
 	/* Now we can release the buffer */
 	ReleaseBuffer(buffer);
 
@@ -4142,6 +4151,11 @@ heap_update_internal(Relation relation, ItemPointer otid, HeapTuple newtup,
 	 */
 	CacheInvalidateHeapTuple(relation, &oldtup, heaptup);
 
+	if (IsCatalogRelation(relation))
+	{
+		system_relation_modified = true;
+	}
+
 	/* Now we can release the buffer(s) */
 	if (newbuf != buffer)
 		ReleaseBuffer(newbuf);
@@ -6270,6 +6284,11 @@ heap_inplace_update(Relation relation, HeapTuple tuple)
 	 */
 	if (!IsBootstrapProcessingMode())
 		CacheInvalidateHeapTuple(relation, tuple, NULL);
+
+	if (IsCatalogRelation(relation))
+	{
+		system_relation_modified = true;
+	}
 }
 
 #define		FRM_NOOP				0x0001

src/backend/access/transam/xact.c

@@ -32,6 +32,7 @@
 #include "access/xloginsert.h"
 #include "access/xact_storage_tablespace.h"
 #include "access/xlogutils.h"
+#include "catalog/catalog.h"
 #include "catalog/index.h"
 #include "catalog/namespace.h"
 #include "catalog/pg_enum.h"
@@ -2785,6 +2786,8 @@ CommitTransaction(void)
 	if (Gp_role == GP_ROLE_EXECUTE && !Gp_is_writer)
 		elog(DEBUG1,"CommitTransaction: called as segment Reader");
 
+	system_relation_modified = false;
+
 	/*
 	 * Do pre-commit processing that involves calling user-defined code, such
 	 * as triggers.  SECURITY_RESTRICTED_OPERATION contexts must not queue an
@@ -3519,6 +3522,8 @@ AbortTransaction(void)
 	 */
 	s->state = TRANS_ABORT;
 
+	system_relation_modified = false;
+
 	/*
 	 * Reset user ID which might have been changed transiently.  We need this
 	 * to clean up in case control escaped out of a SECURITY DEFINER function

src/backend/catalog/catalog.c

@@ -88,6 +88,7 @@
 
 static bool IsAoSegmentClass(Form_pg_class reltuple);
 static bool IsExtAuxClass(Form_pg_class reltuple);
+bool system_relation_modified = false;
 
 /*
  * Like relpath(), but gets the directory containing the data file

src/backend/cdb/dispatcher/cdbdisp_query.c

@@ -19,6 +19,7 @@
 #include "access/xact.h"
 #include "libpq-fe.h"
 #include "libpq-int.h"
+#include "catalog/catalog.h"
 #include "cdb/cdbconn.h"
 #include "cdb/cdbgang.h"
 #include "cdb/cdbutil.h"
@@ -486,7 +487,8 @@ cdbdisp_dispatchCommandInternal(DispatchCommandQueryParms *pQueryParms,
 	 * To fix this issue, we should drop the idle reader gangs after each
 	 * utility statement which may modify the catalog table.
 	 */
-	ds->destroyIdleReaderGang = true;
+	if (system_relation_modified)
+		ds->destroyIdleReaderGang = true;
 
 	queryText = buildGpQueryString(pQueryParms, &queryTextLength);
 

src/include/catalog/catalog.h

@@ -57,4 +57,6 @@ extern void reldir_and_filename(RelFileNode rnode, BackendId backend, ForkNumber
 					char **dir, char **filename);
 extern char *aorelpathbackend(RelFileNode node, BackendId backend, int32 segno);
 
+extern bool system_relation_modified;
+
 #endif							/* CATALOG_H */