Make a light weight version of DEBUG OBJECT, add FAST option (valkey-…

…io#881)

Adding FAST option to DEBUG OBJECT command.

The light version only shows the light weight infomation,
which mostly O(1). The pre-existing version that show more
stats such as serializedlength sometimes is time consuming.

This should allow looking into debug stats (the key expired
but not deleted), even on huge object, on which we're afraid
to run the command for fear of causing a server freeze.

Somehow like 3ca451c.

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

src/debug.c

@@ -659,9 +659,7 @@ void debugCommand(client *c) {
         sds s = sdsempty();
         s = sdscatprintf(s, "Value at:%p refcount:%d encoding:%s", (void *)val, val->refcount, strenc);
         if (!fast) s = sdscatprintf(s, " serializedlength:%zu", rdbSavedObjectLen(val, c->argv[2], c->db->id));
-        /* Either lru or lfu field could work correctly which depends on server.maxmemory_policy. */
         s = sdscatprintf(s, " lru:%d lru_seconds_idle:%llu", val->lru, estimateObjectIdleTime(val) / 1000);
-        s = sdscatprintf(s, " lfu_freq:%lu lfu_access_time_minutes:%u", LFUDecrAndReturn(val), val->lru >> 8);
         s = sdscatprintf(s, "%s", extra);
         addReplyStatusLength(c, s, sdslen(s));
         sdsfree(s);