Add check for nextval in CTE inlining to prevent inlining of queries containing nextval

src/backend/distributed/planner/cte_inline.c

@@ -16,6 +16,7 @@
 #include "nodes/nodeFuncs.h"
 #include "optimizer/optimizer.h"
 #include "rewrite/rewriteManip.h"
+#include "distributed/citus_ruleutils.h"   /* Ensure this header declares contain_nextval_expression_walker */
 
 #include "pg_version_compat.h"
 #include "pg_version_constants.h"
@@ -48,6 +49,9 @@ static bool RecursivelyInlineCteWalker(Node *node, void *context);
 static void InlineCTEsInQueryTree(Query *query);
 static bool QueryTreeContainsInlinableCteWalker(Node *node, void *context);
 
+static bool
+QueryContainsNextval2(Query *q);
+
 
 /*
  * RecursivelyInlineCtesInQueryTree gets a query and recursively traverses the
@@ -93,44 +97,77 @@ RecursivelyInlineCteWalker(Node *node, void *context)
 }
 
 
-/*
- * InlineCTEsInQueryTree gets a query tree and tries to inline CTEs as subqueries
- * in the query tree.
- *
- * Most of the code is coming from PostgreSQL's CTE inlining logic, there are very
- * few additions that Citus added, which are already commented in the code.
- */
 void
 InlineCTEsInQueryTree(Query *query)
 {
-	ListCell *cteCell = NULL;
+    ListCell *cteCell = NULL;
+    List *copyOfCteList = list_copy(query->cteList);
 
-	/* iterate on the copy of the list because we'll be modifying query->cteList */
-	List *copyOfCteList = list_copy(query->cteList);
-	foreach(cteCell, copyOfCteList)
-	{
-		CommonTableExpr *cte = (CommonTableExpr *) lfirst(cteCell);
+    foreach(cteCell, copyOfCteList)
+    {
+        CommonTableExpr *cte = (CommonTableExpr *) lfirst(cteCell);
 
-		/*
-		 * First, make sure that Postgres is OK to inline the CTE. Later, check for
-		 * distributed query planning constraints that might prevent inlining.
-		 */
-		if (PostgreSQLCTEInlineCondition(cte, query->commandType))
-		{
-			elog(DEBUG1, "CTE %s is going to be inlined via "
-						 "distributed planning", cte->ctename);
+        /* Extra check: if the CTE query contains nextval, do not inline it */
+        if (QueryContainsNextval2((Query *) cte->ctequery))
+        {
+            elog(DEBUG1, "CTE \"%s\" contains nextval; materializing it instead of inlining", cte->ctename);
+            continue;
+        }
 
-			/* do the hard work of cte inlining */
-			inline_cte(query, cte);
+        /* Standard PostgreSQL inline condition */
+        if (PostgreSQLCTEInlineCondition(cte, query->commandType))
+        {
+            elog(DEBUG1, "CTE \"%s\" is going to be inlined via distributed planning", cte->ctename);
+            inline_cte(query, cte);
 
-			/* clean-up the necessary fields for distributed planning */
-			cte->cterefcount = 0;
-			query->cteList = list_delete_ptr(query->cteList, cte);
-		}
-	}
+            /* Reset reference count and remove from cteList */
+            cte->cterefcount = 0;
+            query->cteList = list_delete_ptr(query->cteList, cte);
+        }
+    }
 }
 
 
+static bool
+QueryContainsNextval2(Query *q)
+{
+    ListCell *lc = NULL;
+
+    /* Check the target list */
+    foreach(lc, q->targetList)
+    {
+        TargetEntry *tle = (TargetEntry *) lfirst(lc);
+        if (contain_nextval_expression_walker((Node *) tle->expr, NULL))
+            return true;
+    }
+
+    /* Check the WHERE clause (jointree quals) */
+    if (q->jointree && q->jointree->quals &&
+        contain_nextval_expression_walker((Node *) q->jointree->quals, NULL))
+        return true;
+
+    /* Recursively check subqueries in the range table */
+    foreach(lc, q->rtable)
+    {
+        RangeTblEntry *rte = (RangeTblEntry *) lfirst(lc);
+        if (rte->rtekind == RTE_SUBQUERY && rte->subquery != NULL)
+        {
+            if (QueryContainsNextval2(rte->subquery))
+                return true;
+        }
+    }
+
+    /* Optionally, check havingQual if needed */
+    if (q->havingQual &&
+        contain_nextval_expression_walker((Node *) q->havingQual, NULL))
+        return true;
+
+    return false;
+}
+
+
+
+
 /*
  * QueryTreeContainsInlinableCTE recursively traverses the queryTree, and returns true
  * if any of the (sub)queries in the queryTree contains at least one CTE.