Grouped vectorized aggregate (#289)

src/columnar.h

@@ -173,6 +173,8 @@ extern bool columnar_enable_bloom_filter;	/* bloom equality skipping (I7) */
 
 /* Phase 6 GUCs (spec 8.3) */
 extern bool columnar_enable_vectorization;	/* vectorized aggregate path */
+extern bool columnar_enable_group_vectorization;	/* GROUP BY vectorized agg (#289) */
+extern int columnar_groupagg_max_groups;	/* plan-time group-count cap (#289) */
 extern bool columnar_enable_read_stream;	/* stream/prefetch block reads (PG17+) */
 extern bool columnar_enable_index_only_scan;	/* allow index-only scans (gap 28) */
 extern bool columnar_enable_projection_scan;	/* scan a covering projection (gap 26) */
@@ -772,6 +774,7 @@ extern void ColumnarCustomScanInit(void);
  */
 extern const CustomScanMethods columnar_scan_methods;
 extern Node *ColumnarCreateAggScanState(CustomScan *cscan);
+extern Node *ColumnarCreateGroupAggScanState(CustomScan *cscan);
 
 /*
  * Build the chunk-group skip scan keys from a plan's restriction clauses.

src/columnar_customscan.c

@@ -703,7 +703,17 @@ static Node *
 ColumnarCreateScanState(CustomScan *cscan)
 {
 	if (cscan->scan.scanrelid == 0)
+	{
+		/*
+		 * Both upper aggregate paths are scanrelid==0 custom scans sharing these
+		 * registered methods. The grouped path (#289) carries a length-5
+		 * custom_private (rti, quals, relid, keys, output map); the ungrouped
+		 * path carries length 3.
+		 */
+		if (list_length(cscan->custom_private) == 5)
+			return ColumnarCreateGroupAggScanState(cscan);
 		return ColumnarCreateAggScanState(cscan);
+	}
 
 	return ColumnarCreateBaseScanState(cscan);
 }

src/columnar_tableam.c

@@ -2244,6 +2244,28 @@ _PG_init(void)
 							 0,
 							 NULL, NULL, NULL);
 
+	DefineCustomBoolVariable("pgcolumnar.enable_group_vectorization",
+							 "Use the vectorized aggregate fast path for GROUP BY queries.",
+							 NULL,
+							 &columnar_enable_group_vectorization,
+							 false,
+							 PGC_USERSET,
+							 0,
+							 NULL, NULL, NULL);
+
+	DefineCustomIntVariable("pgcolumnar.groupagg_max_groups",
+							"Cap on the actual group count the grouped vectorized "
+							"aggregate builds before it stops with an error.",
+							"Enforced at execution against the real number of groups, "
+							"not the planner's estimate: over the cap the query errors "
+							"rather than falling back, since the plan is fixed by then. "
+							"Raise it, or turn off pgcolumnar.enable_group_vectorization.",
+							&columnar_groupagg_max_groups,
+							1000000, 1, INT_MAX,
+							PGC_USERSET,
+							0,
+							NULL, NULL, NULL);
+
 	DefineCustomBoolVariable("pgcolumnar.enable_bloom_filter",
 							 "Skip chunk groups on equality using per-chunk bloom filters.",
 							 NULL,