Streams: fix XREAD ready-key signaling.

With lists we need to signal only on key creation, but streams can
provide data to clients listening at every new item added.
To make this slightly more efficient we now track different classes of
blocked clients to avoid signaling keys when there is nobody listening.
A typical case is when the stream is used as a time series DB and
accessed only by range with XRANGE.

src/blocked.c

@@ -102,7 +102,8 @@ int getTimeoutFromObjectOrReply(client *c, robj *object, mstime_t *timeout, int
 void blockClient(client *c, int btype) {
     c->flags |= CLIENT_BLOCKED;
     c->btype = btype;
-    server.bpop_blocked_clients++;
+    server.blocked_clients++;
+    server.blocked_clients_by_type[btype]++;
 }
 
 /* This function is called in the beforeSleep() function of the event loop
@@ -145,9 +146,10 @@ void unblockClient(client *c) {
     }
     /* Clear the flags, and put the client in the unblocked list so that
      * we'll process new commands in its query buffer ASAP. */
+    server.blocked_clients--;
+    server.blocked_clients_by_type[c->btype]--;
     c->flags &= ~CLIENT_BLOCKED;
     c->btype = BLOCKED_NONE;
-    server.bpop_blocked_clients--;
     /* The client may already be into the unblocked list because of a previous
      * blocking operation, don't add back it into the list multiple times. */
     if (!(c->flags & CLIENT_UNBLOCKED)) {

src/db.c

@@ -169,8 +169,7 @@ void dbAdd(redisDb *db, robj *key, robj *val) {
     int retval = dictAdd(db->dict, copy, val);
 
     serverAssertWithInfo(NULL,key,retval == DICT_OK);
-    if (val->type == OBJ_LIST || val->type == OBJ_STREAM)
-        signalKeyAsReady(db, key);
+    if (val->type == OBJ_LIST) signalKeyAsReady(db, key);
     if (server.cluster_enabled) slotToKeyAdd(key);
 }
 

src/server.c

@@ -1426,7 +1426,9 @@ void initServerConfig(void) {
     server.active_defrag_running = 0;
     server.notify_keyspace_events = 0;
     server.maxclients = CONFIG_DEFAULT_MAX_CLIENTS;
-    server.bpop_blocked_clients = 0;
+    server.blocked_clients = 0;
+    memset(server.blocked_clients_by_type,0,
+           sizeof(server.blocked_clients_by_type));
     server.maxmemory = CONFIG_DEFAULT_MAXMEMORY;
     server.maxmemory_policy = CONFIG_DEFAULT_MAXMEMORY_POLICY;
     server.maxmemory_samples = CONFIG_DEFAULT_MAXMEMORY_SAMPLES;
@@ -2929,7 +2931,7 @@ sds genRedisInfoString(char *section) {
             "blocked_clients:%d\r\n",
             listLength(server.clients)-listLength(server.slaves),
             lol, bib,
-            server.bpop_blocked_clients);
+            server.blocked_clients);
     }
 
     /* Memory */

src/server.h

@@ -257,6 +257,7 @@ typedef long long mstime_t; /* millisecond time type. */
 #define BLOCKED_WAIT 2    /* WAIT for synchronous replication. */
 #define BLOCKED_MODULE 3  /* Blocked by a loadable module. */
 #define BLOCKED_STREAM 4  /* XREAD. */
+#define BLOCKED_NUM 5     /* Number of blocked states. */
 
 /* Client request types */
 #define PROTO_REQ_INLINE 1
@@ -1130,7 +1131,8 @@ struct redisServer {
     int lfu_log_factor;             /* LFU logarithmic counter factor. */
     int lfu_decay_time;             /* LFU counter decay factor. */
     /* Blocked clients */
-    unsigned int bpop_blocked_clients; /* Number of clients blocked by lists */
+    unsigned int blocked_clients;   /* # of clients executing a blocking cmd.*/
+    unsigned int blocked_clients_by_type[BLOCKED_NUM];
     list *unblocked_clients; /* list of clients to unblock before next loop */
     list *ready_keys;        /* List of readyList structures for BLPOP & co */
     /* Sort parameters - qsort_r() is only available under BSD so we

src/t_stream.c

@@ -354,6 +354,8 @@ void xaddCommand(client *c) {
     signalModifiedKey(c->db,c->argv[1]);
     notifyKeyspaceEvent(NOTIFY_HASH,"xadd",c->argv[1],c->db->id);
     server.dirty++;
+    if (server.blocked_clients_by_type[BLOCKED_STREAM])
+        signalKeyAsReady(c->db, c->argv[1]);
 }
 
 /* XRANGE key start end [COUNT <n>] */