From d663d4399e767223e454302ea90d04f78b2f9d29 Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Mon, 17 Mar 2014 17:18:40 +0200
Subject: [PATCH] Fix thinko: have trueTriConsistentFn return GIN_TRUE.
While we're at it, also improve comments in ginlogic.c.
---
src/backend/access/gin/ginlogic.c | 35 ++++++++++++++++++-------------
1 file changed, 21 insertions(+), 14 deletions(-)
diff --git a/src/backend/access/gin/ginlogic.c b/src/backend/access/gin/ginlogic.c
index b13ce4c4fba..e6d9e051696 100644
--- a/src/backend/access/gin/ginlogic.c
+++ b/src/backend/access/gin/ginlogic.c
@@ -3,18 +3,25 @@
* ginlogic.c
* routines for performing binary- and ternary-logic consistent checks.
*
- * A GIN operator class provides a consistent function which checks if a
- * tuple matches a qual, when the given set of keys are present in the tuple.
- * The consistent function is passed a TRUE/FALSE argument for every key,
- * indicating if that key is present, and it returns TRUE or FALSE. However,
- * a GIN scan can apply various optimizations, if it can determine that an
- * item matches or doesn't match, even if it doesn't know if some of the keys
- * are present or not. Hence, it's useful to have a ternary-logic consistent
- * function, where each key can be TRUE (present), FALSE (not present),
- * or MAYBE (don't know if present). This file provides such a ternary-logic
- * consistent function, implemented by calling the regular boolean consistent
- * function many times, with all the MAYBE arguments set to all combinations
- * of TRUE and FALSE.
+ * A GIN operator class can provide a boolean or ternary consistent
+ * function, or both. This file provides both boolean and ternary
+ * interfaces to the rest of the GIN code, even if only one of them is
+ * implemented by the opclass.
+ *
+ * Providing a boolean interface when the opclass implements only the
+ * ternary function is straightforward - just call the ternary function
+ * with the check-array as is, and map the GIN_TRUE, GIN_FALSE, GIN_MAYBE
+ * return codes to TRUE, FALSE and TRUE+recheck, respectively. Providing
+ * a ternary interface when the opclass only implements a boolean function
+ * is implemented by calling the boolean function many times, with all the
+ * MAYBE arguments set to all combinations of TRUE and FALSE (up to a
+ * certain number of MAYBE arguments).
+ *
+ * (A boolean function is enough to determine if an item matches, but a
+ * GIN scan can apply various optimizations if it can determine that an
+ * item matches or doesn't match, even if it doesn't know if some of the
+ * keys are present or not. That's what the ternary consistent function
+ * is used for.)
*
*
* Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
@@ -43,7 +50,7 @@
#define MAX_MAYBE_ENTRIES 4
/*
- * A dummy consistent function for an EVERYTHING key. Just claim it matches.
+ * Dummy consistent functions for an EVERYTHING key. Just claim it matches.
*/
static bool
trueConsistentFn(GinScanKey key)
@@ -54,7 +61,7 @@ trueConsistentFn(GinScanKey key)
static GinLogicValue
trueTriConsistentFn(GinScanKey key)
{
- return GIN_MAYBE;
+ return GIN_TRUE;
}
/*
--
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