Repair failure with SubPlans in multi-row VALUES lists.

When nodeValuesscan.c was written, it was impossible to have a SubPlan in
VALUES --- any sub-SELECT there would have to be uncorrelated and thereby
would produce an InitPlan instead.  We therefore took a shortcut in the
logic that throws away a ValuesScan's per-row expression evaluation data
structures.  This was broken by the introduction of LATERAL however; a
sub-SELECT containing a lateral reference produces a correlated SubPlan.

The cleanest fix for this would be to give up the optimization of
discarding the expression eval state.  But that still seems pretty
unappetizing for long VALUES lists.  It seems to work to just prevent
the subexpressions from hooking into the ValuesScan node's subPlan
list, so let's do that and see how well it works.  (If this breaks,
due to additional connections between the subexpressions and the outer
query structures, we might consider compromises like throwing away data
only for VALUES rows not containing SubPlans.)

Per bug #14924 from Christian Duta.  Back-patch to 9.3 where LATERAL
was introduced.

Discussion: https://postgr.es/m/20171124120836[email protected]

diff --git a/src/backend/executor/nodeValuesscan.c b/src/backend/executor/nodeValuesscan.c
index d49a4733865083e70e2fbf1395730a96ebfc4e5b..def7926ecb82b0bcdeb01bf3de90151eb84e1bee 100644 (file)
--- a/src/backend/executor/nodeValuesscan.c
+++ b/src/backend/executor/nodeValuesscan.c
@@ -91,6 +91,7 @@ ValuesNext(ValuesScanState *node)
    if (exprlist)
    {
        MemoryContext oldContext;
+       List       *oldsubplans;
        List       *exprstatelist;
        Datum      *values;
        bool       *isnull;
@@ -113,12 +114,22 @@ ValuesNext(ValuesScanState *node)
        oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
 
        /*
-        * Pass NULL, not my plan node, because we don't want anything in this
-        * transient state linking into permanent state.  The only possibility
-        * is a SubPlan, and there shouldn't be any (any subselects in the
-        * VALUES list should be InitPlans).
+        * The expressions might contain SubPlans (this is currently only
+        * possible if there's a sub-select containing a LATERAL reference,
+        * otherwise sub-selects in a VALUES list should be InitPlans). Those
+        * subplans will want to hook themselves into our subPlan list, which
+        * would result in a corrupted list after we delete the eval state. We
+        * can work around this by saving and restoring the subPlan list.
+        * (There's no need for the functionality that would be enabled by
+        * having the list entries, since the SubPlans aren't going to be
+        * re-executed anyway.)
         */
-       exprstatelist = (List *) ExecInitExpr((Expr *) exprlist, NULL);
+       oldsubplans = node->ss.ps.subPlan;
+       node->ss.ps.subPlan = NIL;
+
+       exprstatelist = (List *) ExecInitExpr((Expr *) exprlist, &node->ss.ps);
+
+       node->ss.ps.subPlan = oldsubplans;
 
        /* parser should have checked all sublists are the same length */
        Assert(list_length(exprstatelist) == slot->tts_tupleDescriptor->natts);

diff --git a/src/test/regress/expected/subselect.out b/src/test/regress/expected/subselect.out
index 01c91308f33351711f542508767d1e55bedf5b6f..7532c272a52ce28ddbd85b71d7dc46e8089b289b 100644 (file)
--- a/src/test/regress/expected/subselect.out
+++ b/src/test/regress/expected/subselect.out
@@ -710,6 +710,36 @@ select exists(select * from nocolumns);
  f
 (1 row)
 
+--
+-- Check behavior with a SubPlan in VALUES (bug #14924)
+--
+select val.x
+  from generate_series(1,10) as s(i),
+  lateral (
+    values ((select s.i + 1)), (s.i + 101)
+  ) as val(x)
+where s.i < 10 and (select val.x) < 110;
+  x  
+-----
+   2
+ 102
+   3
+ 103
+   4
+ 104
+   5
+ 105
+   6
+ 106
+   7
+ 107
+   8
+ 108
+   9
+ 109
+  10
+(17 rows)
+
 --
 -- Check sane behavior with nested IN SubLinks
 --

diff --git a/src/test/regress/sql/subselect.sql b/src/test/regress/sql/subselect.sql
index 56707e26bbf4499462a2d972a5d46a2600746c1b..81cf79928b3d8bcf795e97d478e875bda1b99960 100644 (file)
--- a/src/test/regress/sql/subselect.sql
+++ b/src/test/regress/sql/subselect.sql
@@ -412,6 +412,16 @@ explain (verbose, costs off)
 create temp table nocolumns();
 select exists(select * from nocolumns);
 
+--
+-- Check behavior with a SubPlan in VALUES (bug #14924)
+--
+select val.x
+  from generate_series(1,10) as s(i),
+  lateral (
+    values ((select s.i + 1)), (s.i + 101)
+  ) as val(x)
+where s.i < 10 and (select val.x) < 110;
+
 --
 -- Check sane behavior with nested IN SubLinks
 --