Set scan direction appropriately for SubPlans (bug #15336)

When executing a SubPlan in an expression, the EState's direction
field was left alone, resulting in an attempt to execute the subplan
backwards if it was encountered during a backwards scan of a cursor.
Also, though much less likely, it was possible to reach the execution
of an InitPlan while in backwards-scan state.

Repair by saving/restoring estate->es_direction and forcing forward
scan mode in the relevant places.

Backpatch all the way, since this has been broken since 8.3 (prior to
commit c7ff7663e, SubPlans had their own EStates rather than sharing
the parent plan's, so there was no confusion over scan direction).

Per bug #15336 reported by Vladimir Baranoff; analysis and patch by
me, review by Tom Lane.

Discussion: https://postgr.es/m/153449812167.1304.1741624125628126322@wrigleys.postgresql.org

diff --git a/src/backend/executor/nodeSubplan.c b/src/backend/executor/nodeSubplan.c
index fe10e809dfb8859fea0da273f22d5b7df130f11a..84d1b34c16b38628edbadf0f64812afd48f0aa5c 100644 (file)
--- a/src/backend/executor/nodeSubplan.c
+++ b/src/backend/executor/nodeSubplan.c
@@ -65,6 +65,9 @@ ExecSubPlan(SubPlanState *node,
            bool *isNull)
 {
    SubPlan    *subplan = node->subplan;
+   EState     *estate = node->planstate->state;
+   ScanDirection dir = estate->es_direction;
+   Datum       retval;
 
    CHECK_FOR_INTERRUPTS();
 
@@ -77,11 +80,19 @@ ExecSubPlan(SubPlanState *node,
    if (subplan->setParam != NIL && subplan->subLinkType != MULTIEXPR_SUBLINK)
        elog(ERROR, "cannot set parent params from subquery");
 
+   /* Force forward-scan mode for evaluation */
+   estate->es_direction = ForwardScanDirection;
+
    /* Select appropriate evaluation strategy */
    if (subplan->useHashTable)
-       return ExecHashSubPlan(node, econtext, isNull);
+       retval = ExecHashSubPlan(node, econtext, isNull);
    else
-       return ExecScanSubPlan(node, econtext, isNull);
+       retval = ExecScanSubPlan(node, econtext, isNull);
+
+   /* restore scan direction */
+   estate->es_direction = dir;
+
+   return retval;
 }
 
 /*
@@ -918,6 +929,8 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
    SubPlan    *subplan = node->subplan;
    PlanState  *planstate = node->planstate;
    SubLinkType subLinkType = subplan->subLinkType;
+   EState     *estate = planstate->state;
+   ScanDirection dir = estate->es_direction;
    MemoryContext oldcontext;
    TupleTableSlot *slot;
    ListCell   *pvar;
@@ -931,6 +944,12 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
    if (subLinkType == CTE_SUBLINK)
        elog(ERROR, "CTE subplans should not be executed via ExecSetParamPlan");
 
+   /*
+    * Enforce forward scan direction regardless of caller. It's hard but not
+    * impossible to get here in backward scan, so make it work anyway.
+    */
+   estate->es_direction = ForwardScanDirection;
+
    /* Initialize ArrayBuildStateAny in caller's context, if needed */
    if (subLinkType == ARRAY_SUBLINK)
        astate = initArrayResultAny(subplan->firstColType,
@@ -1083,6 +1102,9 @@ ExecSetParamPlan(SubPlanState *node, ExprContext *econtext)
    }
 
    MemoryContextSwitchTo(oldcontext);
+
+   /* restore scan direction */
+   estate->es_direction = dir;
 }
 
 /*

diff --git a/src/test/regress/expected/subselect.out b/src/test/regress/expected/subselect.out
index 796426c66e22b11f8128b2d684b6aa46a9f91ff7..2725c03fb95a912e11da08d52af701a8ccb5f721 100644 (file)
--- a/src/test/regress/expected/subselect.out
+++ b/src/test/regress/expected/subselect.out
@@ -1085,3 +1085,20 @@ NOTICE:  x = 9, y = 13
 (3 rows)
 
 drop function tattle(x int, y int);
+--
+-- Ensure that backward scan direction isn't propagated into
+-- expression subqueries (bug #15336)
+--
+begin;
+declare c1 scroll cursor for
+ select * from generate_series(1,4) i
+  where i <> all (values (2),(3));
+move forward all in c1;
+fetch backward all in c1;
+ i 
+---
+ 4
+ 1
+(2 rows)
+
+commit;

diff --git a/src/test/regress/sql/subselect.sql b/src/test/regress/sql/subselect.sql
index 15035afd0b0b0aada2631f1ff976b21cdb5ab42f..ca856116021598163775ed3007fc8e2aa6246cad 100644 (file)
--- a/src/test/regress/sql/subselect.sql
+++ b/src/test/regress/sql/subselect.sql
@@ -568,3 +568,19 @@ select * from
   where tattle(x, u);
 
 drop function tattle(x int, y int);
+
+--
+-- Ensure that backward scan direction isn't propagated into
+-- expression subqueries (bug #15336)
+--
+
+begin;
+
+declare c1 scroll cursor for
+ select * from generate_series(1,4) i
+  where i <> all (values (2),(3));
+
+move forward all in c1;
+fetch backward all in c1;
+
+commit;