Performance improvements in cnfify(): get rid of exponential

space consumption in pull_args, and avoid doing the full CNF transform on
operands of operator clauses, where it's really not particularly helpful.
This answers the TODO item about large numbers of OR clauses, at least
partially.  I was able to do a ten-thousand-OR-clause query with about
20Mb memory consumption ... it took an obscenely long time, but it worked...

src/backend/optimizer/prep/prepqual.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepqual.c,v 1.17 1999/07/16 04:59:21 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepqual.c,v 1.18 1999/09/07 03:47:06 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -15,14 +15,12 @@
 
 #include "postgres.h"
 
-
-
 #include "nodes/makefuncs.h"
 #include "optimizer/clauses.h"
 #include "optimizer/prep.h"
 #include "utils/lsyscache.h"
 
-static Expr *pull_args(Expr *qual);
+static Expr *flatten_andors(Expr *qual, bool deep);
 static List *pull_ors(List *orlist);
 static List *pull_ands(List *andlist);
 static Expr *find_nots(Expr *qual);
@@ -31,7 +29,6 @@ static Expr *normalize(Expr *qual);
 static List *or_normalize(List *orlist);
 static List *distribute_args(List *item, List *args);
 static List *qual_cleanup(Expr *qual);
-static List *remove_ands(Expr *qual);
 static List *remove_duplicates(List *list);
 
 /*****************************************************************************
@@ -54,9 +51,11 @@ static List *remove_duplicates(List *list);
  *	  Convert a qualification to conjunctive normal form by applying
  *	  successive normalizations.
  *
- * Returns the modified qualification with an extra level of nesting.
+ * Returns the modified qualification.
  *
- * If 'removeAndFlag' is true then it removes the explicit ANDs.
+ * If 'removeAndFlag' is true then it removes explicit AND at the top level,
+ * producing a list of implicitly-ANDed conditions.  Otherwise, a normal
+ * boolean expression is returned.
  *
  * NOTE: this routine is called by the planner (removeAndFlag = true)
  *		and from the rule manager (removeAndFlag = false).
@@ -69,17 +68,26 @@ cnfify(Expr *qual, bool removeAndFlag)
 
 	if (qual != NULL)
 	{
-		newqual = find_nots(pull_args(qual));
-		newqual = normalize(pull_args(newqual));
-		newqual = (Expr *) qual_cleanup(pull_args(newqual));
-		newqual = pull_args(newqual);;
+		/* Flatten AND and OR groups throughout the tree.
+		 * This improvement is always worthwhile.
+		 */
+		newqual = flatten_andors(qual, true);
+		/* Push down NOTs.  We do this only in the top-level boolean
+		 * expression, without examining arguments of operators/functions.
+		 */
+		newqual = find_nots(newqual);
+		/* Pushing NOTs could have brought AND/ORs together, so do
+		 * another flatten_andors (only in the top level); then normalize.
+		 */
+		newqual = normalize(flatten_andors(newqual, false));
+		/* Do we need a flatten here?  Anyway, clean up after normalize. */
+		newqual = (Expr *) qual_cleanup(flatten_andors(newqual, false));
+		/* This flatten is almost surely a waste of time... */
+		newqual = flatten_andors(newqual, false);
 
 		if (removeAndFlag)
 		{
-			if (and_clause((Node *) newqual))
-				newqual = (Expr *) remove_ands(newqual);
-			else
-				newqual = (Expr *) remove_ands(make_andclause(lcons(newqual, NIL)));
+			newqual = (Expr *) make_ands_implicit(newqual);
 		}
 	}
 
@@ -88,9 +96,8 @@ cnfify(Expr *qual, bool removeAndFlag)
 
 /*
  * find_nots
- *	  Traverse the qualification, looking for 'not's to take care of.
- *	  For 'not' clauses, remove the 'not' and push it down to the clauses'
- *	  descendants.
+ *	  Traverse the qualification, looking for 'NOT's to take care of.
+ *	  For 'NOT' clauses, apply push_not() to try to push down the 'NOT'.
  *	  For all other clause types, simply recurse.
  *
  * Returns the modified qualification.
@@ -102,6 +109,8 @@ find_nots(Expr *qual)
 	if (qual == NULL)
 		return NULL;
 
+#ifdef NOT_USED
+	/* recursing into operator expressions is probably not worth it. */
 	if (is_opclause((Node *) qual))
 	{
 		Expr	   *left = (Expr *) get_leftop(qual);
@@ -117,20 +126,20 @@ find_nots(Expr *qual)
 							   lcons(find_nots(left),
 									 NIL));
 	}
-	else if (and_clause((Node *) qual))
+#endif
+	if (and_clause((Node *) qual))
 	{
-		List	   *temp = NIL;
 		List	   *t_list = NIL;
+		List	   *temp;
 
 		foreach(temp, qual->args)
 			t_list = lappend(t_list, find_nots(lfirst(temp)));
-
 		return make_andclause(t_list);
 	}
 	else if (or_clause((Node *) qual))
 	{
-		List	   *temp = NIL;
 		List	   *t_list = NIL;
+		List	   *temp;
 
 		foreach(temp, qual->args)
 			t_list = lappend(t_list, find_nots(lfirst(temp)));
@@ -142,13 +151,91 @@ find_nots(Expr *qual)
 		return qual;
 }
 
+/*
+ * push_nots
+ *	  Push down a 'NOT' as far as possible.
+ *
+ * Input is an expression to be negated (e.g., the argument of a NOT clause).
+ * Returns a new qual equivalent to the negation of the given qual.
+ */
+static Expr *
+push_nots(Expr *qual)
+{
+	if (qual == NULL)
+		return make_notclause(qual); /* XXX is this right?  Or possible? */
+
+	/*
+	 * Negate an operator clause if possible: ("NOT" (< A B)) => (> A B)
+	 * Otherwise, retain the clause as it is (the 'not' can't be pushed
+	 * down any farther).
+	 */
+	if (is_opclause((Node *) qual))
+	{
+		Oper	   *oper = (Oper *) ((Expr *) qual)->oper;
+		Oid			negator = get_negator(oper->opno);
+
+		if (negator)
+		{
+			Oper	   *op = (Oper *) makeOper(negator,
+											   InvalidOid,
+											   oper->opresulttype,
+											   0, NULL);
+			return make_opclause(op, get_leftop(qual), get_rightop(qual));
+		}
+		else
+			return make_notclause(qual);
+	}
+	else if (and_clause((Node *) qual))
+	{
+		/*
+		 * Apply DeMorgan's Laws: ("NOT" ("AND" A B)) => ("OR" ("NOT" A)
+		 * ("NOT" B)) ("NOT" ("OR" A B)) => ("AND" ("NOT" A) ("NOT" B))
+		 * i.e., continue negating down through the clause's descendants.
+		 */
+		List	   *t_list = NIL;
+		List	   *temp;
+
+		foreach(temp, qual->args)
+			t_list = lappend(t_list, push_nots(lfirst(temp)));
+		return make_orclause(t_list);
+	}
+	else if (or_clause((Node *) qual))
+	{
+		List	   *t_list = NIL;
+		List	   *temp;
+
+		foreach(temp, qual->args)
+			t_list = lappend(t_list, push_nots(lfirst(temp)));
+		return make_andclause(t_list);
+	}
+	else if (not_clause((Node *) qual))
+	{
+		/*
+		 * Another 'not' cancels this 'not', so eliminate the 'not' and
+		 * stop negating this branch.  But search the subexpression for
+		 * more 'not's to simplify.
+		 */
+		return find_nots(get_notclausearg(qual));
+	}
+	else
+	{
+		/*
+		 * We don't know how to negate anything else, place a 'not' at
+		 * this level.
+		 */
+		return make_notclause(qual);
+	}
+}
+
 /*
  * normalize
  *	  Given a qualification tree with the 'not's pushed down, convert it
  *	  to a tree in CNF by repeatedly applying the rule:
  *				("OR" A ("AND" B C))  => ("AND" ("OR" A B) ("OR" A C))
  *	  bottom-up.
- *	  Note that 'or' clauses will always be turned into 'and' clauses.
+ *	  Note that 'or' clauses will always be turned into 'and' clauses
+ *	  if they contain any 'and' subclauses.  XXX this is not always
+ *	  an improvement...
  *
  * Returns the modified qualification.
  *
@@ -159,25 +246,11 @@ normalize(Expr *qual)
 	if (qual == NULL)
 		return NULL;
 
-	if (is_opclause((Node *) qual))
-	{
-		Expr	   *left = (Expr *) get_leftop(qual);
-		Expr	   *right = (Expr *) get_rightop(qual);
-
-		if (right)
-			return make_clause(qual->opType, qual->oper,
-							   lcons(normalize(left),
-									 lcons(normalize(right),
-										   NIL)));
-		else
-			return make_clause(qual->opType, qual->oper,
-							   lcons(normalize(left),
-									 NIL));
-	}
-	else if (and_clause((Node *) qual))
+	/* We used to recurse into opclauses here, but I see no reason to... */
+	if (and_clause((Node *) qual))
 	{
-		List	   *temp = NIL;
 		List	   *t_list = NIL;
+		List	   *temp;
 
 		foreach(temp, qual->args)
 			t_list = lappend(t_list, normalize(lfirst(temp)));
@@ -187,8 +260,8 @@ normalize(Expr *qual)
 	{
 		/* XXX - let form, maybe incorrect */
 		List	   *orlist = NIL;
-		List	   *temp = NIL;
-		bool		has_andclause = FALSE;
+		bool		has_andclause = false;
+		List	   *temp;
 
 		foreach(temp, qual->args)
 			orlist = lappend(orlist, normalize(lfirst(temp)));
@@ -196,15 +269,14 @@ normalize(Expr *qual)
 		{
 			if (and_clause(lfirst(temp)))
 			{
-				has_andclause = TRUE;
+				has_andclause = true;
 				break;
 			}
 		}
-		if (has_andclause == TRUE)
+		if (has_andclause)
 			return make_andclause(or_normalize(orlist));
 		else
 			return make_orclause(orlist);
-
 	}
 	else if (not_clause((Node *) qual))
 		return make_notclause(normalize(get_notclausearg(qual)));
@@ -216,10 +288,9 @@ normalize(Expr *qual)
  * qual_cleanup
  *	  Fix up a qualification by removing duplicate entries (left over from
  *	  normalization), and by removing 'and' and 'or' clauses which have only
- *	  one valid expr (e.g., ("AND" A) => A).
- *
- * Returns the modified qualfication.
+ *	  one remaining subexpr (e.g., ("AND" A) => A).
  *
+ * Returns the modified qualification.
  */
 static List *
 qual_cleanup(Expr *qual)
@@ -244,9 +315,9 @@ qual_cleanup(Expr *qual)
 	}
 	else if (and_clause((Node *) qual))
 	{
-		List	   *temp = NIL;
 		List	   *t_list = NIL;
-		List	   *new_and_args = NIL;
+		List	   *temp;
+		List	   *new_and_args;
 
 		foreach(temp, qual->args)
 			t_list = lappend(t_list, qual_cleanup(lfirst(temp)));
@@ -260,16 +331,15 @@ qual_cleanup(Expr *qual)
 	}
 	else if (or_clause((Node *) qual))
 	{
-		List	   *temp = NIL;
 		List	   *t_list = NIL;
-		List	   *new_or_args = NIL;
+		List	   *temp;
+		List	   *new_or_args;
 
 		foreach(temp, qual->args)
 			t_list = lappend(t_list, qual_cleanup(lfirst(temp)));
 
 		new_or_args = remove_duplicates(t_list);
 
-
 		if (length(new_or_args) > 1)
 			return (List *) make_orclause(new_or_args);
 		else
@@ -281,54 +351,93 @@ qual_cleanup(Expr *qual)
 		return (List *) qual;
 }
 
-/*
- * pull_args
- *	  Given a qualification, eliminate nested 'and' and 'or' clauses.
+/*--------------------
+ * flatten_andors
+ *	  Given a qualification, simplify nested AND/OR clauses into flat
+ *	  AND/OR clauses with more arguments.
  *
- * Returns the modified qualification.
+ * The parser regards AND and OR as purely binary operators, so a qual like
+ *		(A = 1) OR (A = 2) OR (A = 3) ...
+ * will produce a nested parsetree
+ *		(OR (A = 1) (OR (A = 2) (OR (A = 3) ...)))
+ * In reality, the optimizer and executor regard AND and OR as n-argument
+ * operators, so this tree can be flattened to
+ *		(OR (A = 1) (A = 2) (A = 3) ...)
+ * which is the responsibility of this routine.
+ *
+ * If 'deep' is true, we search the whole tree for AND/ORs to simplify;
+ * if not, we consider only the top-level AND/OR/NOT structure.
  *
+ * Returns the rebuilt expr (note original list structure is not touched).
+ *--------------------
  */
 static Expr *
-pull_args(Expr *qual)
+flatten_andors(Expr *qual, bool deep)
 {
 	if (qual == NULL)
 		return NULL;
 
-	if (is_opclause((Node *) qual))
+	if (and_clause((Node *) qual))
+	{
+		List	   *out_list = NIL;
+		List	   *arg;
+
+		foreach(arg, qual->args)
+		{
+			Expr   *subexpr = flatten_andors((Expr *) lfirst(arg), deep);
+
+			/*
+			 * Note: we can destructively nconc the subexpression's arglist
+			 * because we know the recursive invocation of flatten_andors
+			 * will have built a new arglist not shared with any other expr.
+			 * Otherwise we'd need a listCopy here.
+			 */
+			if (and_clause((Node *) subexpr))
+				out_list = nconc(out_list, subexpr->args);
+			else
+				out_list = lappend(out_list, subexpr);
+		}
+		return make_andclause(out_list);
+	}
+	else if (or_clause((Node *) qual))
+	{
+		List	   *out_list = NIL;
+		List	   *arg;
+
+		foreach(arg, qual->args)
+		{
+			Expr   *subexpr = flatten_andors((Expr *) lfirst(arg), deep);
+
+			/*
+			 * Note: we can destructively nconc the subexpression's arglist
+			 * because we know the recursive invocation of flatten_andors
+			 * will have built a new arglist not shared with any other expr.
+			 * Otherwise we'd need a listCopy here.
+			 */
+			if (or_clause((Node *) subexpr))
+				out_list = nconc(out_list, subexpr->args);
+			else
+				out_list = lappend(out_list, subexpr);
+		}
+		return make_orclause(out_list);
+	}
+	else if (not_clause((Node *) qual))
+		return make_notclause(flatten_andors(get_notclausearg(qual), deep));
+	else if (deep && is_opclause((Node *) qual))
 	{
 		Expr	   *left = (Expr *) get_leftop(qual);
 		Expr	   *right = (Expr *) get_rightop(qual);
 
 		if (right)
 			return make_clause(qual->opType, qual->oper,
-							   lcons(pull_args(left),
-									 lcons(pull_args(right),
+							   lcons(flatten_andors(left, deep),
+									 lcons(flatten_andors(right, deep),
 										   NIL)));
 		else
 			return make_clause(qual->opType, qual->oper,
-							   lcons(pull_args(left),
+							   lcons(flatten_andors(left, deep),
 									 NIL));
 	}
-	else if (and_clause((Node *) qual))
-	{
-		List	   *temp = NIL;
-		List	   *t_list = NIL;
-
-		foreach(temp, qual->args)
-			t_list = lappend(t_list, pull_args(lfirst(temp)));
-		return make_andclause(pull_ands(t_list));
-	}
-	else if (or_clause((Node *) qual))
-	{
-		List	   *temp = NIL;
-		List	   *t_list = NIL;
-
-		foreach(temp, qual->args)
-			t_list = lappend(t_list, pull_args(lfirst(temp)));
-		return make_orclause(pull_ors(t_list));
-	}
-	else if (not_clause((Node *) qual))
-		return make_notclause(pull_args(get_notclausearg(qual)));
 	else
 		return qual;
 }
@@ -338,23 +447,31 @@ pull_args(Expr *qual)
  *	  Pull the arguments of an 'or' clause nested within another 'or'
  *	  clause up into the argument list of the parent.
  *
- * Returns the modified list.
+ * Input is the arglist of an OR clause.
+ * Returns the rebuilt arglist (note original list structure is not touched).
  */
 static List *
 pull_ors(List *orlist)
 {
-	if (orlist == NIL)
-		return NIL;
+	List	   *out_list = NIL;
+	List	   *arg;
 
-	if (or_clause(lfirst(orlist)))
+	foreach(arg, orlist)
 	{
-		List	   *args = ((Expr *) lfirst(orlist))->args;
+		Expr   *subexpr = (Expr *) lfirst(arg);
 
-		return (pull_ors(nconc(copyObject((Node *) args),
-							   copyObject((Node *) lnext(orlist)))));
+		/*
+		 * Note: we can destructively nconc the subexpression's arglist
+		 * because we know the recursive invocation of pull_ors
+		 * will have built a new arglist not shared with any other expr.
+		 * Otherwise we'd need a listCopy here.
+		 */
+		if (or_clause((Node *) subexpr))
+			out_list = nconc(out_list, pull_ors(subexpr->args));
+		else
+			out_list = lappend(out_list, subexpr);
 	}
-	else
-		return lcons(lfirst(orlist), pull_ors(lnext(orlist)));
+	return out_list;
 }
 
 /*
@@ -367,94 +484,25 @@ pull_ors(List *orlist)
 static List *
 pull_ands(List *andlist)
 {
-	if (andlist == NIL)
-		return NIL;
+	List	   *out_list = NIL;
+	List	   *arg;
 
-	if (and_clause(lfirst(andlist)))
-	{
-		List	   *args = ((Expr *) lfirst(andlist))->args;
-
-		return (pull_ands(nconc(copyObject((Node *) args),
-								copyObject((Node *) lnext(andlist)))));
-	}
-	else
-		return lcons(lfirst(andlist), pull_ands(lnext(andlist)));
-}
-
-/*
- * push_nots
- *	  Negate the descendants of a 'not' clause.
- *
- * Returns the modified qualification.
- *
- */
-static Expr *
-push_nots(Expr *qual)
-{
-	if (qual == NULL)
-		return NULL;
-
-	/*
-	 * Negate an operator clause if possible: ("NOT" (< A B)) => (> A B)
-	 * Otherwise, retain the clause as it is (the 'not' can't be pushed
-	 * down any farther).
-	 */
-	if (is_opclause((Node *) qual))
-	{
-		Oper	   *oper = (Oper *) ((Expr *) qual)->oper;
-		Oid			negator = get_negator(oper->opno);
-
-		if (negator)
-		{
-			Oper	   *op = (Oper *) makeOper(negator,
-											   InvalidOid,
-											   oper->opresulttype,
-											   0, NULL);
-
-			op->op_fcache = (FunctionCache *) NULL;
-			return make_opclause(op, get_leftop(qual), get_rightop(qual));
-		}
-		else
-			return make_notclause(qual);
-	}
-	else if (and_clause((Node *) qual))
+	foreach(arg, andlist)
 	{
+		Expr   *subexpr = (Expr *) lfirst(arg);
 
 		/*
-		 * Apply DeMorgan's Laws: ("NOT" ("AND" A B)) => ("OR" ("NOT" A)
-		 * ("NOT" B)) ("NOT" ("OR" A B)) => ("AND" ("NOT" A) ("NOT" B))
-		 * i.e., continue negating down through the clause's descendants.
+		 * Note: we can destructively nconc the subexpression's arglist
+		 * because we know the recursive invocation of pull_ands
+		 * will have built a new arglist not shared with any other expr.
+		 * Otherwise we'd need a listCopy here.
 		 */
-		List	   *temp = NIL;
-		List	   *t_list = NIL;
-
-		foreach(temp, qual->args)
-			t_list = lappend(t_list, push_nots(lfirst(temp)));
-		return make_orclause(t_list);
-	}
-	else if (or_clause((Node *) qual))
-	{
-		List	   *temp = NIL;
-		List	   *t_list = NIL;
-
-		foreach(temp, qual->args)
-			t_list = lappend(t_list, push_nots(lfirst(temp)));
-		return make_andclause(t_list);
+		if (and_clause((Node *) subexpr))
+			out_list = nconc(out_list, pull_ands(subexpr->args));
+		else
+			out_list = lappend(out_list, subexpr);
 	}
-	else if (not_clause((Node *) qual))
-
-		/*
-		 * Another 'not' cancels this 'not', so eliminate the 'not' and
-		 * stop negating this branch.
-		 */
-		return find_nots(get_notclausearg(qual));
-	else
-
-		/*
-		 * We don't know how to negate anything else, place a 'not' at
-		 * this level.
-		 */
-		return make_notclause(qual);
+	return out_list;
 }
 
 /*
@@ -478,16 +526,19 @@ or_normalize(List *orlist)
 	foreach(temp, orlist)
 	{
 		if (and_clause(lfirst(temp)))
+		{
 			distributable = lfirst(temp);
+			break;
+		}
 	}
 	if (distributable)
 		new_orlist = LispRemove(distributable, orlist);
 
 	if (new_orlist)
 	{
-		return (or_normalize(lcons(distribute_args(lfirst(new_orlist),
-										 ((Expr *) distributable)->args),
-								   lnext(new_orlist))));
+		return or_normalize(lcons(distribute_args(lfirst(new_orlist),
+										((Expr *) distributable)->args),
+								  lnext(new_orlist)));
 	}
 	else
 		return orlist;
@@ -504,104 +555,40 @@ or_normalize(List *orlist)
 static List *
 distribute_args(List *item, List *args)
 {
-	List	   *or_list = NIL;
-	List	   *n_list = NIL;
-	List	   *temp = NIL;
 	List	   *t_list = NIL;
+	List	   *temp;
 
 	if (args == NULL)
 		return item;
 
 	foreach(temp, args)
 	{
+		List	   *n_list;
+
 		n_list = or_normalize(pull_ors(lcons(item,
-											 lcons(lfirst(temp), NIL))));
-		or_list = (List *) make_orclause(n_list);
-		t_list = lappend(t_list, or_list);
+											 lcons(lfirst(temp),
+												   NIL))));
+		t_list = lappend(t_list, make_orclause(n_list));
 	}
 	return (List *) make_andclause(t_list);
 }
 
-/*
- * remove_ands
- *	  Remove the explicit "AND"s from the qualification:
- *				("AND" A B) => (A B)
- *
- * RETURNS : qual
- * MODIFIES: qual
- */
-static List *
-remove_ands(Expr *qual)
-{
-	List	   *t_list = NIL;
-
-	if (qual == NULL)
-		return NIL;
-	if (is_opclause((Node *) qual))
-	{
-		Expr	   *left = (Expr *) get_leftop(qual);
-		Expr	   *right = (Expr *) get_rightop(qual);
-
-		if (right)
-			return (List *) make_clause(qual->opType, qual->oper,
-										lcons(remove_ands(left),
-											  lcons(remove_ands(right),
-													NIL)));
-		else
-			return (List *) make_clause(qual->opType, qual->oper,
-										lcons(remove_ands(left),
-											  NIL));
-	}
-	else if (and_clause((Node *) qual))
-	{
-		List	   *temp = NIL;
-
-		foreach(temp, qual->args)
-			t_list = lappend(t_list, remove_ands(lfirst(temp)));
-		return t_list;
-	}
-	else if (or_clause((Node *) qual))
-	{
-		List	   *temp = NIL;
-
-		foreach(temp, qual->args)
-			t_list = lappend(t_list, remove_ands(lfirst(temp)));
-		return (List *) make_orclause((List *) t_list);
-	}
-	else if (not_clause((Node *) qual))
-		return (List *) make_notclause((Expr *) remove_ands((Expr *) get_notclausearg(qual)));
-	else
-		return (List *) qual;
-}
-
 /*
  * remove_duplicates
  */
 static List *
 remove_duplicates(List *list)
 {
-	List	   *i;
-	List	   *j;
 	List	   *result = NIL;
-	bool		there_exists_duplicate = false;
+	List	   *i;
 
 	if (length(list) == 1)
 		return list;
 
 	foreach(i, list)
 	{
-		if (i != NIL)
-		{
-			foreach(j, lnext(i))
-			{
-				if (equal(lfirst(i), lfirst(j)))
-					there_exists_duplicate = true;
-			}
-			if (!there_exists_duplicate)
-				result = lappend(result, lfirst(i));
-
-			there_exists_duplicate = false;
-		}
+		if (! member(lfirst(i), result))
+			result = lappend(result, lfirst(i));
 	}
 	return result;
 }