33 * ginlogic.c
44 * routines for performing binary- and ternary-logic consistent checks.
55 *
6- * A GIN operator class provides a consistent function which checks if a
7- * tuple matches a qual, when the given set of keys are present in the tuple.
8- * The consistent function is passed a TRUE/FALSE argument for every key,
9- * indicating if that key is present, and it returns TRUE or FALSE. However,
10- * a GIN scan can apply various optimizations, if it can determine that an
11- * item matches or doesn't match, even if it doesn't know if some of the keys
12- * are present or not. Hence, it's useful to have a ternary-logic consistent
13- * function, where each key can be TRUE (present), FALSE (not present),
14- * or MAYBE (don't know if present). This file provides such a ternary-logic
15- * consistent function, implemented by calling the regular boolean consistent
16- * function many times, with all the MAYBE arguments set to all combinations
17- * of TRUE and FALSE.
6+ * A GIN operator class can provide a boolean or ternary consistent
7+ * function, or both. This file provides both boolean and ternary
8+ * interfaces to the rest of the GIN code, even if only one of them is
9+ * implemented by the opclass.
10+ *
11+ * Providing a boolean interface when the opclass implements only the
12+ * ternary function is straightforward - just call the ternary function
13+ * with the check-array as is, and map the GIN_TRUE, GIN_FALSE, GIN_MAYBE
14+ * return codes to TRUE, FALSE and TRUE+recheck, respectively. Providing
15+ * a ternary interface when the opclass only implements a boolean function
16+ * is implemented by calling the boolean function many times, with all the
17+ * MAYBE arguments set to all combinations of TRUE and FALSE (up to a
18+ * certain number of MAYBE arguments).
19+ *
20+ * (A boolean function is enough to determine if an item matches, but a
21+ * GIN scan can apply various optimizations if it can determine that an
22+ * item matches or doesn't match, even if it doesn't know if some of the
23+ * keys are present or not. That's what the ternary consistent function
24+ * is used for.)
1825 *
1926 *
2027 * Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
4350#define MAX_MAYBE_ENTRIES 4
4451
4552/*
46- *A dummy consistentfunction for an EVERYTHING key. Just claim it matches.
53+ *Dummy consistentfunctions for an EVERYTHING key.
4754 */
4855static bool
4956trueConsistentFn (GinScanKey key )
@@ -54,7 +61,7 @@ trueConsistentFn(GinScanKey key)
5461static GinLogicValue
5562trueTriConsistentFn (GinScanKey key )
5663{
57- return GIN_MAYBE ;
64+ return GIN_TRUE ;
5865}
5966
6067/*