Allow opclasses to provide tri-valued GIN consistent functions.

With the GIN "fast scan" feature, GIN can skip items without fetching all
the keys for them, if it can prove that they don't match regardless of
those keys. So far, it has done the proving by calling the boolean
consistent function with all combinations of TRUE/FALSE for the unfetched
keys, but since that's O(n^2), it becomes unfeasible with more than a few
keys. We can avoid calling consistent with all the combinations, if we can
tell the operator class implementation directly which keys are unknown.

This commit includes a triConsistent function for the built-in array and
tsvector opclasses.

Alexander Korotkov, with some changes by me.

src/backend/utils/adt/tsginidx.c

@@ -15,6 +15,7 @@
 
 #include "access/gin.h"
 #include "access/skey.h"
+#include "miscadmin.h"
 #include "tsearch/ts_type.h"
 #include "tsearch/ts_utils.h"
 #include "utils/builtins.h"
@@ -172,12 +173,12 @@ gin_extract_tsquery(PG_FUNCTION_ARGS)
 typedef struct
 {
 	QueryItem  *first_item;
-	bool	   *check;
+	GinLogicValue *check;
 	int		   *map_item_operand;
 	bool	   *need_recheck;
 } GinChkVal;
 
-static bool
+static GinLogicValue
 checkcondition_gin(void *checkval, QueryOperand *val)
 {
 	GinChkVal  *gcv = (GinChkVal *) checkval;
@@ -194,6 +195,66 @@ checkcondition_gin(void *checkval, QueryOperand *val)
 	return gcv->check[j];
 }
 
+/*
+ * Evaluate tsquery boolean expression using ternary logic.
+ *
+ * chkcond is a callback function used to evaluate each VAL node in the query.
+ * checkval can be used to pass information to the callback. TS_execute doesn't
+ * do anything with it.
+ */
+static GinLogicValue
+TS_execute_ternary(QueryItem *curitem, void *checkval,
+				   GinLogicValue (*chkcond) (void *checkval, QueryOperand *val))
+{
+	GinLogicValue val1, val2, result;
+	/* since this function recurses, it could be driven to stack overflow */
+	check_stack_depth();
+
+	if (curitem->type == QI_VAL)
+		return chkcond(checkval, (QueryOperand *) curitem);
+
+	switch (curitem->qoperator.oper)
+	{
+		case OP_NOT:
+			result = TS_execute_ternary(curitem + 1, checkval, chkcond);
+			if (result == GIN_MAYBE)
+				return result;
+			return !result;
+
+		case OP_AND:
+			val1 = TS_execute_ternary(curitem + curitem->qoperator.left,
+															checkval, chkcond);
+			if (val1 == GIN_FALSE)
+				return GIN_FALSE;
+			val2 = TS_execute_ternary(curitem + 1, checkval, chkcond);
+			if (val2 == GIN_FALSE)
+				return GIN_FALSE;
+			if (val1 == GIN_TRUE && val2 == GIN_TRUE)
+				return GIN_TRUE;
+			else
+				return GIN_MAYBE;
+
+		case OP_OR:
+			val1 = TS_execute_ternary(curitem + curitem->qoperator.left,
+															checkval, chkcond);
+			if (val1 == GIN_TRUE)
+				return GIN_TRUE;
+			val2 = TS_execute_ternary(curitem + 1, checkval, chkcond);
+			if (val2 == GIN_TRUE)
+				return GIN_TRUE;
+			if (val1 == GIN_FALSE && val2 == GIN_FALSE)
+				return GIN_FALSE;
+			else
+				return GIN_MAYBE;
+
+		default:
+			elog(ERROR, "unrecognized operator: %d", curitem->qoperator.oper);
+	}
+
+	/* not reachable, but keep compiler quiet */
+	return false;
+}
+
 Datum
 gin_tsquery_consistent(PG_FUNCTION_ARGS)
 {
@@ -233,6 +294,45 @@ gin_tsquery_consistent(PG_FUNCTION_ARGS)
 	PG_RETURN_BOOL(res);
 }
 
+Datum
+gin_tsquery_triconsistent(PG_FUNCTION_ARGS)
+{
+	GinLogicValue *check = (GinLogicValue *) PG_GETARG_POINTER(0);
+
+	/* StrategyNumber strategy = PG_GETARG_UINT16(1); */
+	TSQuery		query = PG_GETARG_TSQUERY(2);
+
+	/* int32	nkeys = PG_GETARG_INT32(3); */
+	Pointer    *extra_data = (Pointer *) PG_GETARG_POINTER(4);
+	GinLogicValue res = GIN_FALSE;
+	bool		recheck;
+
+	/* The query requires recheck only if it involves weights */
+	if (query->size > 0)
+	{
+		QueryItem  *item;
+		GinChkVal	gcv;
+
+		/*
+		 * check-parameter array has one entry for each value (operand) in the
+		 * query.
+		 */
+		gcv.first_item = item = GETQUERY(query);
+		gcv.check = check;
+		gcv.map_item_operand = (int *) (extra_data[0]);
+		gcv.need_recheck = &recheck;
+
+		res = TS_execute_ternary(GETQUERY(query),
+								 &gcv,
+								 checkcondition_gin);
+
+		if (res == GIN_TRUE && recheck)
+			res = GIN_MAYBE;
+	}
+
+	PG_RETURN_GIN_LOGIC_VALUE(res);
+}
+
 /*
  * Formerly, gin_extract_tsvector had only two arguments.  Now it has three,
  * but we still need a pg_proc entry with two args to support reloading