From dd071ff6c95cbb7427e5f0c3a6ca84e3c672d87a Mon Sep 17 00:00:00 2001
From: "zhaozhao.zz" <zhaozhao.zz@alibaba-inc.com>
Date: Wed, 25 Jul 2018 18:13:34 +0800
Subject: [PATCH] optimize flushdb, avoid useless loops

---
 src/db.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/db.c b/src/db.c
index 055af71b..39686f1b 100644
--- a/src/db.c
+++ b/src/db.c
@@ -329,7 +329,7 @@ robj *dbUnshareStringValue(redisDb *db, robj *key, robj *o) {
  * database(s). Otherwise -1 is returned in the specific case the
  * DB number is out of range, and errno is set to EINVAL. */
 long long emptyDb(int dbnum, int flags, void(callback)(void*)) {
-    int j, async = (flags & EMPTYDB_ASYNC);
+    int async = (flags & EMPTYDB_ASYNC);
     long long removed = 0;
 
     if (dbnum < -1 || dbnum >= server.dbnum) {
@@ -337,7 +337,10 @@ long long emptyDb(int dbnum, int flags, void(callback)(void*)) {
         return -1;
     }
 
-    for (j = 0; j < server.dbnum; j++) {
+    int j = dbnum == -1 ? 0 : dbnum;
+    int dbmax = dbnum == -1 ? server.dbnum : dbnum+1;
+
+    for (; j < dbmax; j++) {
         if (dbnum != -1 && dbnum != j) continue;
         removed += dictSize(server.db[j].dict);
         if (async) {