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.

2011-09-14 15:17:04 +02:00
parent b7bf29059e
commit 67f594f9b5
1 changed files with 6 additions and 1 deletions
@@ -519,7 +519,12 @@ 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);