Make a light weight version of DEBUG OBJECT, add FAST option (#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 <[email protected]>

src/debug.c

@@ -425,8 +425,10 @@ void debugCommand(client *c) {
             "MALLCTL-STR <key> [<val>]",
             "    Get or set a malloc tuning string.",
 #endif
-            "OBJECT <key>",
+            "OBJECT <key> [fast]",
             "    Show low level info about `key` and associated value.",
+            "    Some fields of the default behavior may be time consuming to fetch,",
+            "    and `fast` can be passed to avoid fetching them.",
             "DROP-CLUSTER-PACKET-FILTER <packet-type>",
             "    Drop all packets that match the filtered type. Set to -1 allow all packets.",
             "CLOSE-CLUSTER-LINK-ON-PACKET-DROP <0|1>",
@@ -603,11 +605,14 @@ void debugCommand(client *c) {
     } else if (!strcasecmp(c->argv[1]->ptr, "close-cluster-link-on-packet-drop") && c->argc == 3) {
         server.debug_cluster_close_link_on_packet_drop = atoi(c->argv[2]->ptr);
         addReply(c, shared.ok);
-    } else if (!strcasecmp(c->argv[1]->ptr, "object") && c->argc == 3) {
+    } else if (!strcasecmp(c->argv[1]->ptr, "object") && (c->argc == 3 || c->argc == 4)) {
         dictEntry *de;
         robj *val;
         char *strenc;
 
+        int fast = 0;
+        if (c->argc == 4 && !strcasecmp(c->argv[3]->ptr, "fast")) fast = 1;
+
         if ((de = dbFind(c->db, c->argv[2]->ptr)) == NULL) {
             addReplyErrorObject(c, shared.nokeyerr);
             return;
@@ -638,22 +643,25 @@ void debugCommand(client *c) {
             used = snprintf(nextra, remaining, " ql_compressed:%d", compressed);
             nextra += used;
             remaining -= used;
-            /* Add total uncompressed size */
-            unsigned long sz = 0;
-            for (quicklistNode *node = ql->head; node; node = node->next) {
-                sz += node->sz;
+            if (!fast) {
+                /* Add total uncompressed size */
+                unsigned long sz = 0;
+                for (quicklistNode *node = ql->head; node; node = node->next) {
+                    sz += node->sz;
+                }
+                used = snprintf(nextra, remaining, " ql_uncompressed_size:%lu", sz);
+                nextra += used;
+                remaining -= used;
             }
-            used = snprintf(nextra, remaining, " ql_uncompressed_size:%lu", sz);
-            nextra += used;
-            remaining -= used;
         }
 
-        addReplyStatusFormat(c,
-                             "Value at:%p refcount:%d "
-                             "encoding:%s serializedlength:%zu "
-                             "lru:%d lru_seconds_idle:%llu%s",
-                             (void *)val, val->refcount, strenc, rdbSavedObjectLen(val, c->argv[2], c->db->id),
-                             val->lru, estimateObjectIdleTime(val) / 1000, extra);
+        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));
+        s = sdscatprintf(s, " lru:%d lru_seconds_idle:%llu", val->lru, estimateObjectIdleTime(val) / 1000);
+        s = sdscatprintf(s, "%s", extra);
+        addReplyStatusLength(c, s, sdslen(s));
+        sdsfree(s);
     } else if (!strcasecmp(c->argv[1]->ptr, "sdslen") && c->argc == 3) {
         dictEntry *de;
         robj *val;