From 9e087a298dc798b5664654d0934d27762e76092e Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Wed, 14 Sep 2011 15:10:28 +0200
Subject: [PATCH] Optimize LRANGE to scan the list starting from the head or
 the tail in order to traverse the minimal number of elements. Thanks to
 Didier Spezia for noticing the problem and providing a patch.

---
 src/t_list.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/t_list.c b/src/t_list.c
index 64e917a41..1d046f403 100644
--- a/src/t_list.c
+++ b/src/t_list.c
@@ -514,7 +514,12 @@ void lrangeCommand(redisClient *c) {
             p = ziplistNext(o->ptr,p);
         }
     } else if (o->encoding == REDIS_ENCODING_LINKEDLIST) {
-        listNode *ln = listIndex(o->ptr,start);
+        listNode *ln;
+
+        /* If we are nearest to the end of the list, reach the element
+         * starting from tail and going backward, as it is faster. */
+        if (start > llen/2) start -= llen;
+        ln = listIndex(o->ptr,start);
 
         while(rangelen--) {
             addReplyBulk(c,ln->value);
-- 
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