Reduce rewriteClientCommandVector usage on EXPIRE command (#11602)

There is overhead on Redis 7.0 EXPIRE command that is not present on 6.2.7.

We could see that on the unstable profile there are around 7% of CPU cycles
spent on rewriteClientCommandVector that are not present on 6.2.7.
This was introduced in #8474.
This PR reduces the overhead by using 2X rewriteClientCommandArgument instead of
rewriteClientCommandVector. In this scenario rewriteClientCommandVector creates 4 arguments.
the above usage of rewriteClientCommandArgument reduces the overhead in half.

This PR should also improve PEXPIREAT performance by avoiding at all
rewriteClientCommandArgument usage.

Co-authored-by: Oran Agra <oran@redislabs.com>
(cherry picked from commit c3fb48da8b76ee143d1c380ccf9899752607c5d5)

1 files changed, 13 insertions, 4 deletions

diff --git a/src/expire.c b/src/expire.c
index a6a40450e..eff55208b 100644
--- a/src/expire.c
+++ b/src/expire.c
@@ -651,10 +651,19 @@ void expireGenericCommand(client *c, long long basetime, int unit) {
     } else {
         setExpire(c,c->db,key,when);
         addReply(c,shared.cone);
-        /* Propagate as PEXPIREAT millisecond-timestamp */
-        robj *when_obj = createStringObjectFromLongLong(when);
-        rewriteClientCommandVector(c, 3, shared.pexpireat, key, when_obj);
-        decrRefCount(when_obj);
+        /* Propagate as PEXPIREAT millisecond-timestamp
+         * Only rewrite the command arg if not already PEXPIREAT */
+        if (c->cmd->proc != pexpireatCommand) {
+            rewriteClientCommandArgument(c,0,shared.pexpireat);
+        }
+
+        /* Avoid creating a string object when it's the same as argv[2] parameter  */
+        if (basetime != 0 || unit == UNIT_SECONDS) {
+            robj *when_obj = createStringObjectFromLongLong(when);
+            rewriteClientCommandArgument(c,2,when_obj);
+            decrRefCount(when_obj);
+        }
+
         signalModifiedKey(c,c->db,key);
         notifyKeyspaceEvent(NOTIFY_GENERIC,"expire",key,c->db->id);
         server.dirty++;