From 12c5af03b8b2d868fd35f4c1142162695f8dd41c Mon Sep 17 00:00:00 2001
From: Binbin <binloveplay1314@qq.com>
Date: Wed, 6 Nov 2024 10:32:00 +0800
Subject: [PATCH] Remove empty DB check branch in KEYS command (#1259)

We don't think we really care about optimizing for the empty DB case,
which should be uncommon. Adding branches hurts branch prediction.

Signed-off-by: Binbin <binloveplay1314@qq.com>
---
 src/db.c                |  5 -----
 tests/unit/keyspace.tcl | 15 +++++++++++++++
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/db.c b/src/db.c
index ceb3105f9b..3e0e5a2e63 100644
--- a/src/db.c
+++ b/src/db.c
@@ -830,11 +830,6 @@ void keysCommand(client *c) {
     kvstoreDictIterator *kvs_di = NULL;
     kvstoreIterator *kvs_it = NULL;
     if (pslot != -1) {
-        if (!kvstoreDictSize(c->db->keys, pslot)) {
-            /* Requested slot is empty */
-            setDeferredArrayLen(c, replylen, 0);
-            return;
-        }
         kvs_di = kvstoreGetDictSafeIterator(c->db->keys, pslot);
     } else {
         kvs_it = kvstoreIteratorInit(c->db->keys);
diff --git a/tests/unit/keyspace.tcl b/tests/unit/keyspace.tcl
index ba55c1b8ea..1936f5e217 100644
--- a/tests/unit/keyspace.tcl
+++ b/tests/unit/keyspace.tcl
@@ -47,6 +47,10 @@ start_server {tags {"keyspace"}} {
         r dbsize
     } {0}
 
+    test {KEYS with empty DB} {
+        assert_equal {} [r keys *]
+    }
+
     test "DEL against expired key" {
         r debug set-active-expire 0
         r setex keyExpire 1 valExpire
@@ -554,3 +558,14 @@ foreach {type large} [array get largevalue] {
         r KEYS [string repeat "*?" 50000]
     } {}
 }
+
+start_cluster 1 0 {tags {"keyspace external:skip cluster"}} {
+    test {KEYS with empty DB in cluster mode} {
+        assert_equal {} [r keys *]
+        assert_equal {} [r keys foo*]
+    }
+
+    test {KEYS with empty slot in cluster mode} {
+        assert_equal {} [r keys foo]
+    }
+}