Speedup INFO by counting client memory incrementally.faster-info

Related to #5145.

Design note: clients may change type when they turn into replicas or are
moved into the Pub/Sub category and so forth. Moreover the recomputation
of the bytes used is problematic for obvious reasons: it changes
continuously, so as a conservative way to avoid accumulating errors,
each client remembers the contribution it gave to the sum, and removes
it when it is freed or before updating it with the new memory usage.

1 files changed, 9 insertions, 24 deletions

diff --git a/src/object.c b/src/object.c
index 11e335afc..52d5b11f5 100644
--- a/src/object.c
+++ b/src/object.c
@@ -974,30 +974,15 @@ struct redisMemOverhead *getMemoryOverheadData(void) {
     mh->repl_backlog = mem;
     mem_total += mem;
 
-    mem = 0;
-    if (listLength(server.clients)) {
-        listIter li;
-        listNode *ln;
-        size_t mem_normal = 0, mem_slaves = 0;
-
-        listRewind(server.clients,&li);
-        while((ln = listNext(&li))) {
-            size_t mem_curr = 0;
-            client *c = listNodeValue(ln);
-            int type = getClientType(c);
-            mem_curr += getClientOutputBufferMemoryUsage(c);
-            mem_curr += sdsAllocSize(c->querybuf);
-            mem_curr += sizeof(client);
-            if (type == CLIENT_TYPE_SLAVE)
-                mem_slaves += mem_curr;
-            else
-                mem_normal += mem_curr;
-        }
-        mh->clients_slaves = mem_slaves;
-        mh->clients_normal = mem_normal;
-        mem = mem_slaves + mem_normal;
-    }
-    mem_total+=mem;
+    /* Computing the memory used by the clients would be O(N) if done
+     * here online. We use our values computed incrementally by
+     * clientsCronTrackClientsMemUsage(). */
+    mh->clients_slaves = server.stat_clients_type_memory[CLIENT_TYPE_SLAVE];
+    mh->clients_normal = server.stat_clients_type_memory[CLIENT_TYPE_MASTER]+
+                         server.stat_clients_type_memory[CLIENT_TYPE_PUBSUB]+
+                         server.stat_clients_type_memory[CLIENT_TYPE_NORMAL];
+    mem_total += mh->clients_slaves;
+    mem_total += mh->clients_normal;
 
     mem = 0;
     if (server.aof_state != AOF_OFF) {