Make replica CLUSTER RESET flush async based on lazyfree-lazy-user-fl…

…ush (valkey-io#1190)

Currently, if the replica has a lot of data, CLUSTER RESET
will block for a while and report the slowlog, and it seems
that there is no harm in making it async so external components
can be easier when monitoring it.

Signed-off-by: Binbin <binloveplay1314@qq.com>
Co-authored-by: Ping Xie <pingxie@outlook.com>

src/cluster_legacy.c

@@ -1230,7 +1230,7 @@ void clusterReset(int hard) {
     if (nodeIsReplica(myself)) {
         clusterSetNodeAsPrimary(myself);
         replicationUnsetPrimary();
-        emptyData(-1, EMPTYDB_NO_FLAGS, NULL);
+        emptyData(-1, server.lazyfree_lazy_user_flush ? EMPTYDB_ASYNC : EMPTYDB_NO_FLAGS, NULL);
     }
 
     /* Close slots, reset manual failover state. */

valkey.conf

@@ -1308,7 +1308,11 @@ lazyfree-lazy-user-del yes
 # deletion, which can be controlled by passing the [SYNC|ASYNC] flags into the
 # commands. When neither flag is passed, this directive will be used to determine
 # if the data should be deleted asynchronously.
-
+#
+# When a replica performs a node reset via CLUSTER RESET, the entire
+# database content is removed to allow the node to become an empty primary.
+# This directive also determines whether the data should be deleted asynchronously.
+#
 # There are many problems with running flush synchronously. Even in single CPU
 # environments, the thread managers should balance between the freeing and
 # serving incoming requests. The default value is yes.