From 16559b461521625271430d7d4926b632f3a326dd Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Fri, 3 Oct 2014 11:53:57 +0100
Subject: [PATCH] INCR: Modify incremented object in-place when possible.

However we don't try to do this if the integer is already inside a range
representable with a shared integer.

The performance gain appears to be around ~15% in micro benchmarks,
however in the long run this also helps to improve locality, so should
have more, hard to measure, benefits.
---
 src/t_string.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/t_string.c b/src/t_string.c
index f0669381..74c05793 100644
--- a/src/t_string.c
+++ b/src/t_string.c
@@ -337,11 +337,21 @@ void incrDecrCommand(redisClient *c, long long incr) {
         return;
     }
     value += incr;
-    new = createStringObjectFromLongLong(value);
-    if (o)
-        dbOverwrite(c->db,c->argv[1],new);
-    else
-        dbAdd(c->db,c->argv[1],new);
+
+    if (o && o->refcount == 1 && o->encoding == REDIS_ENCODING_INT &&
+        (value < 0 || value >= REDIS_SHARED_INTEGERS) &&
+        value >= LONG_MIN && value <= LONG_MAX)
+    {
+        new = o;
+        o->ptr = (void*)((long)value);
+    } else {
+        new = createStringObjectFromLongLong(value);
+        if (o) {
+            dbOverwrite(c->db,c->argv[1],new);
+        } else {
+            dbAdd(c->db,c->argv[1],new);
+        }
+    }
     signalModifiedKey(c->db,c->argv[1]);
     notifyKeyspaceEvent(REDIS_NOTIFY_STRING,"incrby",c->argv[1],c->db->id);
     server.dirty++;