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Turns out that my recent elimination of the 'redundant' flatten_andors()
code in prepqual.c had a small drawback: the flatten_andors code was able to cope with deeply nested AND/OR structures (like 10000 ORs in a row), whereas eval_const_expressions tends to recurse until it overruns the stack. Revise eval_const_expressions so that it doesn't choke on deeply nested ANDs or ORs.
This commit is contained in:
Tom Lane
parent
25434e32cb
commit
56c8877291
@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.195 2005/04/14 21:44:09 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.196 2005/04/23 04:42:53 tgl Exp $
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*
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* HISTORY
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* AUTHOR DATE MAJOR EVENT
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@ -73,8 +73,10 @@ static bool set_coercionform_dontcare_walker(Node *node, void *context);
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static Node *eval_const_expressions_mutator(Node *node,
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eval_const_expressions_context *context);
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static List *simplify_or_arguments(List *args,
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eval_const_expressions_context *context,
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bool *haveNull, bool *forceTrue);
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static List *simplify_and_arguments(List *args,
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eval_const_expressions_context *context,
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bool *haveNull, bool *forceFalse);
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static Expr *simplify_boolean_equality(List *args);
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static Expr *simplify_function(Oid funcid, Oid result_type, List *args,
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@ -1466,16 +1468,6 @@ eval_const_expressions_mutator(Node *node,
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if (IsA(node, BoolExpr))
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{
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BoolExpr *expr = (BoolExpr *) node;
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List *args;
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/*
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* Reduce constants in the BoolExpr's arguments. We know args is
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* either NIL or a List node, so we can call
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* expression_tree_mutator directly rather than recursing to self.
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*/
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args = (List *) expression_tree_mutator((Node *) expr->args,
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eval_const_expressions_mutator,
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(void *) context);
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switch (expr->boolop)
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{
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@ -1485,7 +1477,7 @@ eval_const_expressions_mutator(Node *node,
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bool haveNull = false;
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bool forceTrue = false;
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newargs = simplify_or_arguments(args,
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newargs = simplify_or_arguments(expr->args, context,
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&haveNull, &forceTrue);
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if (forceTrue)
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return makeBoolConst(true, false);
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@ -1506,7 +1498,7 @@ eval_const_expressions_mutator(Node *node,
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bool haveNull = false;
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bool forceFalse = false;
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newargs = simplify_and_arguments(args,
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newargs = simplify_and_arguments(expr->args, context,
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&haveNull, &forceFalse);
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if (forceFalse)
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return makeBoolConst(false, false);
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@ -1522,25 +1514,31 @@ eval_const_expressions_mutator(Node *node,
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return (Node *) make_andclause(newargs);
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}
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case NOT_EXPR:
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Assert(list_length(args) == 1);
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if (IsA(linitial(args), Const))
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{
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Const *const_input = (Const *) linitial(args);
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Node *arg;
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/* NOT NULL => NULL */
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if (const_input->constisnull)
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return makeBoolConst(false, true);
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/* otherwise pretty easy */
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return makeBoolConst(!DatumGetBool(const_input->constvalue),
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false);
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Assert(list_length(expr->args) == 1);
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arg = eval_const_expressions_mutator(linitial(expr->args),
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context);
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if (IsA(arg, Const))
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{
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Const *const_input = (Const *) arg;
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/* NOT NULL => NULL */
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if (const_input->constisnull)
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return makeBoolConst(false, true);
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/* otherwise pretty easy */
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return makeBoolConst(!DatumGetBool(const_input->constvalue),
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false);
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}
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else if (not_clause(arg))
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{
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/* Cancel NOT/NOT */
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return (Node *) get_notclausearg((Expr *) arg);
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}
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/* Else we still need a NOT node */
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return (Node *) make_notclause((Expr *) arg);
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}
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else if (not_clause((Node *) linitial(args)))
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{
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/* Cancel NOT/NOT */
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return (Node *) get_notclausearg((Expr *) linitial(args));
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}
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/* Else we still need a NOT node */
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return (Node *) make_notclause((Expr *) linitial(args));
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default:
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elog(ERROR, "unrecognized boolop: %d",
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(int) expr->boolop);
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@ -1869,33 +1867,87 @@ eval_const_expressions_mutator(Node *node,
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}
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/*
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* Subroutine for eval_const_expressions: scan the arguments of an OR clause
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* Subroutine for eval_const_expressions: process arguments of an OR clause
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*
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* OR arguments are handled as follows:
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* This includes flattening of nested ORs as well as recursion to
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* eval_const_expressions to simplify the OR arguments.
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*
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* After simplification, OR arguments are handled as follows:
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* non constant: keep
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* FALSE: drop (does not affect result)
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* TRUE: force result to TRUE
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* NULL: keep only one
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* We must keep one NULL input because ExecEvalOr returns NULL when no input
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* is TRUE and at least one is NULL.
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*
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* This is split out as a subroutine so that we can recurse to fold sub-ORs
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* into the upper OR clause, thereby ensuring that nested ORs are flattened.
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* is TRUE and at least one is NULL. We don't actually include the NULL
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* here, that's supposed to be done by the caller.
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*
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* The output arguments *haveNull and *forceTrue must be initialized FALSE
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* by the caller. They will be set TRUE if a null constant or true constant,
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* respectively, is detected anywhere in the argument list.
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*/
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static List *
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simplify_or_arguments(List *args, bool *haveNull, bool *forceTrue)
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simplify_or_arguments(List *args,
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eval_const_expressions_context *context,
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bool *haveNull, bool *forceTrue)
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{
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List *newargs = NIL;
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ListCell *larg;
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List *unprocessed_args;
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foreach(larg, args)
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/*
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* Since the parser considers OR to be a binary operator, long OR lists
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* become deeply nested expressions. We must flatten these into long
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* argument lists of a single OR operator. To avoid blowing out the stack
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* with recursion of eval_const_expressions, we resort to some tenseness
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* here: we keep a list of not-yet-processed inputs, and handle flattening
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* of nested ORs by prepending to the to-do list instead of recursing.
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*/
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unprocessed_args = list_copy(args);
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while (unprocessed_args)
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{
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Node *arg = (Node *) lfirst(larg);
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Node *arg = (Node *) linitial(unprocessed_args);
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unprocessed_args = list_delete_first(unprocessed_args);
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/* flatten nested ORs as per above comment */
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if (or_clause(arg))
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{
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List *subargs = list_copy(((BoolExpr *) arg)->args);
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/* overly tense code to avoid leaking unused list header */
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if (!unprocessed_args)
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unprocessed_args = subargs;
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else
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{
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List *oldhdr = unprocessed_args;
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unprocessed_args = list_concat(subargs, unprocessed_args);
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pfree(oldhdr);
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}
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continue;
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}
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/* If it's not an OR, simplify it */
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arg = eval_const_expressions_mutator(arg, context);
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/*
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* It is unlikely but not impossible for simplification of a
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* non-OR clause to produce an OR. Recheck, but don't be
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* too tense about it since it's not a mainstream case.
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* In particular we don't worry about const-simplifying
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* the input twice.
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*/
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if (or_clause(arg))
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{
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List *subargs = list_copy(((BoolExpr *) arg)->args);
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unprocessed_args = list_concat(subargs, unprocessed_args);
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continue;
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}
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/*
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* OK, we have a const-simplified non-OR argument. Process it
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* per comments above.
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*/
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if (IsA(arg, Const))
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{
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Const *const_input = (Const *) arg;
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@ -1914,48 +1966,91 @@ simplify_or_arguments(List *args, bool *haveNull, bool *forceTrue)
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return NIL;
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}
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/* otherwise, we can drop the constant-false input */
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continue;
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}
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else if (or_clause(arg))
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{
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newargs = list_concat(newargs,
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simplify_or_arguments(((BoolExpr *) arg)->args,
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haveNull, forceTrue));
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}
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else
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newargs = lappend(newargs, arg);
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/* else emit the simplified arg into the result list */
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newargs = lappend(newargs, arg);
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}
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return newargs;
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}
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/*
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* Subroutine for eval_const_expressions: scan the arguments of an AND clause
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* Subroutine for eval_const_expressions: process arguments of an AND clause
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*
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* AND arguments are handled as follows:
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* This includes flattening of nested ANDs as well as recursion to
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* eval_const_expressions to simplify the AND arguments.
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*
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* After simplification, AND arguments are handled as follows:
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* non constant: keep
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* TRUE: drop (does not affect result)
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* FALSE: force result to FALSE
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* NULL: keep only one
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* We must keep one NULL input because ExecEvalAnd returns NULL when no input
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* is FALSE and at least one is NULL.
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*
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* This is split out as a subroutine so that we can recurse to fold sub-ANDs
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* into the upper AND clause, thereby ensuring that nested ANDs are flattened.
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* is FALSE and at least one is NULL. We don't actually include the NULL
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* here, that's supposed to be done by the caller.
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*
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* The output arguments *haveNull and *forceFalse must be initialized FALSE
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* by the caller. They will be set TRUE if a null constant or false constant,
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* respectively, is detected anywhere in the argument list.
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*/
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static List *
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simplify_and_arguments(List *args, bool *haveNull, bool *forceFalse)
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simplify_and_arguments(List *args,
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eval_const_expressions_context *context,
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bool *haveNull, bool *forceFalse)
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{
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List *newargs = NIL;
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ListCell *larg;
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List *unprocessed_args;
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foreach(larg, args)
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/* See comments in simplify_or_arguments */
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unprocessed_args = list_copy(args);
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while (unprocessed_args)
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{
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Node *arg = (Node *) lfirst(larg);
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Node *arg = (Node *) linitial(unprocessed_args);
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unprocessed_args = list_delete_first(unprocessed_args);
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/* flatten nested ANDs as per above comment */
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if (and_clause(arg))
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{
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List *subargs = list_copy(((BoolExpr *) arg)->args);
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/* overly tense code to avoid leaking unused list header */
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if (!unprocessed_args)
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unprocessed_args = subargs;
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else
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{
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List *oldhdr = unprocessed_args;
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unprocessed_args = list_concat(subargs, unprocessed_args);
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pfree(oldhdr);
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}
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continue;
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}
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/* If it's not an AND, simplify it */
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arg = eval_const_expressions_mutator(arg, context);
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/*
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* It is unlikely but not impossible for simplification of a
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* non-AND clause to produce an AND. Recheck, but don't be
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* too tense about it since it's not a mainstream case.
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* In particular we don't worry about const-simplifying
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* the input twice.
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*/
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if (and_clause(arg))
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{
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List *subargs = list_copy(((BoolExpr *) arg)->args);
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unprocessed_args = list_concat(subargs, unprocessed_args);
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continue;
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}
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/*
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* OK, we have a const-simplified non-AND argument. Process it
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* per comments above.
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*/
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if (IsA(arg, Const))
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{
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Const *const_input = (Const *) arg;
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@ -1974,15 +2069,11 @@ simplify_and_arguments(List *args, bool *haveNull, bool *forceFalse)
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return NIL;
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}
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/* otherwise, we can drop the constant-true input */
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continue;
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}
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else if (and_clause(arg))
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{
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newargs = list_concat(newargs,
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simplify_and_arguments(((BoolExpr *) arg)->args,
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haveNull, forceFalse));
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}
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else
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newargs = lappend(newargs, arg);
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/* else emit the simplified arg into the result list */
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newargs = lappend(newargs, arg);
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}
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return newargs;
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