Simplify the planner hook for columnar tableam (#257)

At present, we have two planner hooks in columnar_customscan.c and
columnar_planner_hook.c separately.  The first hook only sets
stmt->parallelModeNeeded to zero when the query is a CREATE TABLE AS
statement, so we can simplify this code by moving it to the second one.

columnar/src/backend/columnar/columnar_customscan.c

@@ -38,7 +38,6 @@
 #include "optimizer/pathnode.h"
 #include "optimizer/paths.h"
 #include "optimizer/plancat.h"
-#include "optimizer/planner.h"
 #include "optimizer/restrictinfo.h"
 #if PG_VERSION_NUM >= PG_VERSION_16
 #include "parser/parse_relation.h"
@@ -140,8 +139,6 @@ static void ColumnarSetRelPathlistHook(PlannerInfo *root, RelOptInfo *rel, Index
 									   RangeTblEntry *rte);
 static void ColumnarGetRelationInfoHook(PlannerInfo *root, Oid relationObjectId,
 										bool inhparent, RelOptInfo *rel);
-static PlannedStmt *ColumnarPlannerHook(Query *parse, const char *query_string,
-										int cursorOptions, ParamListInfo boundParams);
 
 static Plan * ColumnarScanPath_PlanCustomPath(PlannerInfo *root,
 											  RelOptInfo *rel,
@@ -188,12 +185,10 @@ static List * set_deparse_context_planstate(List *dpcontext, Node *node,
 
 /* other helpers */
 static List * ColumnarVarNeeded(ColumnarScanState *columnarScanState);
-static bool IsCreateTableAs(const char *query);
 
 /* saved hook value in case of unload */
 static set_rel_pathlist_hook_type PreviousSetRelPathlistHook = NULL;
 static get_relation_info_hook_type PreviousGetRelationInfoHook = NULL;
-static planner_hook_type PreviousPlannerHook = NULL;
 
 static bool EnableColumnarCustomScan = true;
 static bool EnableColumnarQualPushdown = true;
@@ -264,9 +259,6 @@ columnar_customscan_init()
 	PreviousGetRelationInfoHook = get_relation_info_hook;
 	get_relation_info_hook = ColumnarGetRelationInfoHook;
 
-	PreviousPlannerHook = planner_hook;
-	planner_hook = ColumnarPlannerHook;
-
 	/* register customscan specific GUC's */
 	DefineCustomBoolVariable(
 		"columnar.enable_custom_scan",
@@ -330,87 +322,6 @@ columnar_customscan_init()
 	RegisterCustomScanMethods(&ColumnarScanScanMethods);
 }
 
-/*
- * IsCreateTableAs
- *
- * Searches a lower case copy of the query string using strstr to check
- * for the keywords CREATE, TABLE, and AS, in that order.  There can be
- * false positives, but we try to minimize them.
- */
-static
-bool IsCreateTableAs(const char *query)
-{
-	char *c, *t, *a;
-	char *haystack = (char *) palloc(strlen(query) + 1);
-	int16 i;
-
-	/* Create a lower case copy of the string. */
-	for (i = 0; i < strlen(query); i++)
-	{
-		haystack[i] = tolower(query[i]);
-	}
-
-	haystack[i] = '\0';
-
-	c = strstr(haystack, "create");
-	if (c == NULL)
-	{
-		pfree(haystack);
-		return false;
-	}
-
-	t = strstr(c + 6, "table");
-	if (t == NULL)
-	{
-		pfree(haystack);
-		return false;
-	}
-
-	a = strstr(t + 5, "as");
-	if (a == NULL)
-	{
-		pfree(haystack);
-		return false;
-	}
-
-	pfree(haystack);
-
-	return true;
-}
-
-static
-PlannedStmt *ColumnarPlannerHook(Query *parse, const char *query_string,
-										int cursorOptions, ParamListInfo boundParams)
-{
-	PlannedStmt *stmt;
-
-	if (PreviousPlannerHook)
-	{
-		stmt = (*PreviousPlannerHook)(parse, query_string, cursorOptions, boundParams);
-	}
-	else
-	{
-		stmt = standard_planner(parse, query_string, cursorOptions, boundParams);
-	}
-
-	/*
-	 * In the case of a CREATE TABLE AS query, we are not able to successfully
-	 * drop out of a parallel insert situation.  This checks for a CMD_SELECT
-	 * and in that case examines the query string to see if it matches the
-	 * pattern of a CREATE TABLE AS.  If so, set the parallelism to 0 (off).
-	 */
-	if (parse->commandType == CMD_SELECT)
-	{
-		if (IsCreateTableAs(query_string))
-		{
-			stmt->parallelModeNeeded = 0;
-		}
-	}
-
-	return stmt;
-}
-
-
 static void
 ColumnarSetRelPathlistHook(PlannerInfo *root, RelOptInfo *rel, Index rti,
 						   RangeTblEntry *rte)

columnar/src/backend/columnar/columnar_planner_hook.c

@@ -52,6 +52,7 @@ static Oid columnar_tableam_oid = InvalidOid;
 
 static PlannedStmt * ColumnarPlannerHook(Query *parse,  const char *query_string,
 										 int cursorOptions, ParamListInfo boundParams);
+static bool IsCreateTableAs(const char *query);
 
 #if PG_VERSION_NUM >= PG_VERSION_14
 static Plan * PlanTreeMutator(Plan *node, void *context);
@@ -326,6 +327,20 @@ ColumnarPlannerHook(Query *parse,
 	else
 		stmt = standard_planner(parse, query_string, cursorOptions, boundParams);
 
+	/*
+	 * In the case of a CREATE TABLE AS query, we are not able to successfully
+	 * drop out of a parallel insert situation.  This checks for a CMD_SELECT
+	 * and in that case examines the query string to see if it matches the
+	 * pattern of a CREATE TABLE AS.  If so, set the parallelism to 0 (off).
+	 */
+	if (parse->commandType == CMD_SELECT)
+	{
+		if (IsCreateTableAs(query_string))
+		{
+			stmt->parallelModeNeeded = 0;
+		}
+	}
+
 #if PG_VERSION_NUM >= PG_VERSION_14
 	if (!(columnar_enable_vectorization			/* Vectorization should be enabled */
 			|| columnar_index_scan)				/* or Columnar Index Scan */
@@ -382,6 +397,53 @@ ColumnarPlannerHook(Query *parse,
 	return stmt;
 }
 
+/*
+ * IsCreateTableAs
+ *
+ * Searches a lower case copy of the query string using strstr to check
+ * for the keywords CREATE, TABLE, and AS, in that order.  There can be
+ * false positives, but we try to minimize them.
+ */
+static bool
+IsCreateTableAs(const char *query)
+{
+	char *c, *t, *a;
+	char *haystack = (char *) palloc(strlen(query) + 1);
+	int16 i;
+
+	/* Create a lower case copy of the string. */
+	for (i = 0; i < strlen(query); i++)
+	{
+		haystack[i] = tolower(query[i]);
+	}
+
+	haystack[i] = '\0';
+
+	c = strstr(haystack, "create");
+	if (c == NULL)
+	{
+		pfree(haystack);
+		return false;
+	}
+
+	t = strstr(c + 6, "table");
+	if (t == NULL)
+	{
+		pfree(haystack);
+		return false;
+	}
+
+	a = strstr(t + 5, "as");
+	if (a == NULL)
+	{
+		pfree(haystack);
+		return false;
+	}
+
+	pfree(haystack);
+
+	return true;
+}
 
 void columnar_planner_init(void)
 {