Add some recursion and looping defenses in prepjointree.c.

Andrey Lepikhov demonstrated a case where we spend an unreasonable
amount of time in pull_up_subqueries().  Not only is that recursing
with no explicit check for stack overrun, but the code seems not
interruptable by control-C.  Let's stick a CHECK_FOR_INTERRUPTS
there, along with sprinkling some stack depth checks.

An actual fix for the excessive time consumption seems a bit
risky to back-patch; but this isn't, so let's do so.

Discussion: https://postgr.es/m/703c09a2-08f3-d2ec-b33d-dbecd62428b8@postgrespro.ru

diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
index 09a8dd3e93b8ed04d5f0364eade9ce508d3c5ff3..1f20d1885c4e387965154c0b9c9054c712b0a2a1 100644 (file)
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -27,6 +27,7 @@
 
 #include "catalog/pg_type.h"
 #include "funcapi.h"
+#include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
 #include "optimizer/clauses.h"
@@ -235,6 +236,9 @@ static Node *
 pull_up_sublinks_jointree_recurse(PlannerInfo *root, Node *jtnode,
                                  Relids *relids)
 {
+   /* Since this function recurses, it could be driven to stack overflow. */
+   check_stack_depth();
+
    if (jtnode == NULL)
    {
        *relids = NULL;
@@ -732,6 +736,11 @@ pull_up_subqueries_recurse(PlannerInfo *root, Node *jtnode,
                           JoinExpr *lowest_nulling_outer_join,
                           AppendRelInfo *containing_appendrel)
 {
+   /* Since this function recurses, it could be driven to stack overflow. */
+   check_stack_depth();
+   /* Also, since it's a bit expensive, let's check for query cancel. */
+   CHECK_FOR_INTERRUPTS();
+
    Assert(jtnode != NULL);
    if (IsA(jtnode, RangeTblRef))
    {
@@ -1854,6 +1863,9 @@ is_simple_union_all(Query *subquery)
 static bool
 is_simple_union_all_recurse(Node *setOp, Query *setOpQuery, List *colTypes)
 {
+   /* Since this function recurses, it could be driven to stack overflow. */
+   check_stack_depth();
+
    if (IsA(setOp, RangeTblRef))
    {
        RangeTblRef *rtr = (RangeTblRef *) setOp;