From: Robert Haas <rhaas@postgresql.org>
Date: Tue, 29 Apr 2014 19:30:36 +0000 (+0000)
Subject: Cache the results of the last sb_find_leaf operation.
X-Git-Url: http://waps.l3s.uni-hannover.de/gitweb/?a=commitdiff_plain;h=b7bb20a16175162231734c6e6ea8f1e818c91ccc;p=users%2Frhaas%2Fpostgres.git

Cache the results of the last sb_find_leaf operation.

If all the memory we're accessing is in the same 4GB segment of the address
space, this eliminates calls to sb_find_leaf altogether, a significant
savings.  But even if we're ranging across more than one segment, this
should win in cases that have some degree of access locality.
---

diff --git a/src/backend/utils/mmgr/sb_region.c b/src/backend/utils/mmgr/sb_region.c
index 47ad11c266..1c5156337d 100644
--- a/src/backend/utils/mmgr/sb_region.c
+++ b/src/backend/utils/mmgr/sb_region.c
@@ -219,12 +219,24 @@ sb_lookup_region(void *ptr)
 #if SIZEOF_SIZE_T > 4
 	{
 		Size	highbits = p >> 32;
+		static Size last_highbits = 0;
+		static sb_lookup_leaf *last_leaf = NULL;
 
-		leaf = sb_find_leaf(highbits, false);
+		/* Quick test to see if we're in same range as before. */
+		if (last_highbits == highbits && last_leaf != NULL)
+			leaf = last_leaf;
+		else
+		{
+			leaf = sb_find_leaf(highbits, false);
 
-		/* No lookup table for this 4GB range?  OK, no matching region. */
-		if (leaf == NULL)
-			return NULL;
+			/* No lookup table for this 4GB range?  OK, no matching region. */
+			if (leaf == NULL)
+				return NULL;
+
+			/* Remember results of this lookup for next time. */
+			last_highbits = highbits;
+			last_leaf = leaf;
+		}
 	}
 #else
 	leaf = &lookup_root_leaf;