Adding guc to tune the Orca's cost model for sort.

This guc allow us to change the cost of sort and tuning the query plan
generated by Orca for better performance.

src/backend/gpopt/utils/COptTasks.cpp

@@ -906,6 +906,19 @@ COptTasks::SetCostModelParams
 		CDouble dNLJFactor(optimizer_nestloop_factor);
 		pcm->Pcp()->SetParam(pcp->UlId(), dNLJFactor, dNLJFactor - 0.5, dNLJFactor + 0.5);
 	}
+
+	if (optimizer_sort_factor > 1.0 || optimizer_sort_factor < 1.0)
+	{
+		// change sort cost factor
+		ICostModelParams::SCostParam *pcp = NULL;
+		if (OPTIMIZER_GPDB_CALIBRATED == optimizer_cost_model)
+		{
+			pcp = pcm->Pcp()->PcpLookup(CCostModelParamsGPDB::EcpSortTupWidthCostUnit);
+
+			CDouble dSortFactor(optimizer_sort_factor);
+			pcm->Pcp()->SetParam(pcp->UlId(), pcp->DVal() * optimizer_sort_factor, pcp->DLowerBound() * optimizer_sort_factor, pcp->DUpperBound() * optimizer_sort_factor);
+		}
+	}
 }
 
 

src/backend/utils/misc/guc_gp.c

@@ -537,6 +537,7 @@ int			optimizer_samples_number;
 int			optimizer_log_failure;
 double		optimizer_cost_threshold;
 double		optimizer_nestloop_factor;
+double		optimizer_sort_factor;
 bool		optimizer_cte_inlining;
 int			optimizer_cte_inlining_bound;
 double		optimizer_damping_factor_filter;
@@ -4948,6 +4949,16 @@ struct config_real ConfigureNamesReal_gp[] =
 		1024.0, 1.0, DBL_MAX, NULL, NULL
 	},
 
+	{
+		{"optimizer_sort_factor",PGC_USERSET, DEVELOPER_OPTIONS,
+			gettext_noop("set the sort cost factor in the optimizer, 1.0 means same as default, > 1.0 means more costly than default, < 1.0 means means less costly than default"),
+			NULL,
+			GUC_NO_SHOW_ALL | GUC_NOT_IN_SAMPLE
+		},
+		&optimizer_sort_factor,
+		1.0, 0.0, DBL_MAX, NULL, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, 0.0, 0.0, 0.0, NULL, NULL

src/include/utils/guc.h

@@ -447,6 +447,7 @@ extern int	optimizer_samples_number;
 extern int optimizer_log_failure;
 extern double optimizer_cost_threshold;
 extern double optimizer_nestloop_factor;
+extern double optimizer_sort_factor;
 extern bool optimizer_cte_inlining;
 extern int optimizer_cte_inlining_bound;
 extern double optimizer_damping_factor_filter;