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/20171124120836.1463.5310@wrigleys.postgresql.org

diff --git a/src/backend/executor/nodeValuesscan.c b/src/backend/executor/nodeValuesscan.c
index 1a72bfe16002f99ab04195258cc1462a51b06aae..47ba9faa78e06d7820a0d8a223d79ccb52c04baf 100644 (file)
--- a/src/backend/executor/nodeValuesscan.c
+++ b/src/backend/executor/nodeValuesscan.c
@@ -92,6 +92,7 @@ ValuesNext(ValuesScanState *node)
        if (exprlist)
        {
                MemoryContext oldContext;
+               List       *oldsubplans;
                List       *exprstatelist;
                Datum      *values;
                bool       *isnull;
@@ -114,12 +115,22 @@ 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 = ExecInitExprList(exprlist, NULL);
+               oldsubplans = node->ss.ps.subPlan;
+               node->ss.ps.subPlan = NIL;
+
+               exprstatelist = ExecInitExprList(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 992d29bb860daef26b32281f7a645539428344fc..4b893856cfc9613aca2783612a9cb65863c01a94 100644 (file)
--- a/src/test/regress/expected/subselect.out
+++ b/src/test/regress/expected/subselect.out
@@ -840,6 +840,36 @@ 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 0d2dd2f1d8135e9411636e63c68d36795208811e..0100367b8d76595bc1ee1f83605346632003fab8 100644 (file)
--- a/src/test/regress/sql/subselect.sql
+++ b/src/test/regress/sql/subselect.sql
@@ -472,6 +472,16 @@ 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
 --