From 9f8885760b53e6d3952b9c9b41f9e6c48dfa6cec Mon Sep 17 00:00:00 2001
From: Harkrishn Patro <30795839+hpatro@users.noreply.github.com>
Date: Mon, 3 Jan 2022 01:54:47 +0100
Subject: [PATCH] Sharded pubsub implementation (#8621)

This commit implements a sharded pubsub implementation based off of shard channels.

Co-authored-by: Harkrishn Patro <harkrisp@amazon.com>
Co-authored-by: Madelyn Olson <madelyneolson@gmail.com>
---
 redis.conf                                    |   9 +
 src/acl.c                                     |  20 +-
 src/cluster.c                                 | 169 ++++++++-
 src/cluster.h                                 |   5 +
 src/commands.c                                |  70 ++++
 src/commands/pubsub-shardchannels.json        |  23 ++
 src/commands/pubsub-shardnumsub.json          |  16 +
 src/commands/spublish.json                    |  46 +++
 src/commands/ssubscribe.json                  |  42 +++
 src/commands/sunsubscribe.json                |  43 +++
 src/config.c                                  |   1 +
 src/module.c                                  |   1 +
 src/networking.c                              |   4 +
 src/pubsub.c                                  | 350 +++++++++++++++---
 src/redis-cli.c                               |   3 +-
 src/server.c                                  |  10 +-
 src/server.h                                  |  23 +-
 src/tracking.c                                |   6 +
 tests/cluster/cluster.tcl                     |  30 +-
 .../cluster/tests/19-cluster-nodes-slots.tcl  |  21 --
 .../tests/23-multiple-slot-operations.tcl     |   8 +-
 .../tests/25-pubsubshard-slot-migration.tcl   | 171 +++++++++
 tests/cluster/tests/26-pubsubshard.tcl        |  94 +++++
 tests/instances.tcl                           |  10 +
 tests/support/cluster.tcl                     |   6 +-
 tests/test_helper.tcl                         |   1 +
 tests/unit/acl.tcl                            |  54 ++-
 tests/unit/pubsubshard.tcl                    | 213 +++++++++++
 28 files changed, 1343 insertions(+), 106 deletions(-)
 create mode 100644 src/commands/pubsub-shardchannels.json
 create mode 100644 src/commands/pubsub-shardnumsub.json
 create mode 100644 src/commands/spublish.json
 create mode 100644 src/commands/ssubscribe.json
 create mode 100644 src/commands/sunsubscribe.json
 create mode 100644 tests/cluster/tests/25-pubsubshard-slot-migration.tcl
 create mode 100644 tests/cluster/tests/26-pubsubshard.tcl
 create mode 100644 tests/unit/pubsubshard.tcl

diff --git a/redis.conf b/redis.conf
index 7289277cf..8804aac37 100644
--- a/redis.conf
+++ b/redis.conf
@@ -1613,6 +1613,15 @@ lua-time-limit 5000
 #
 # cluster-allow-reads-when-down no
 
+# This option, when set to yes, allows nodes to serve pubsub shard traffic while the
+# the cluster is in a down state, as long as it believes it owns the slots.
+#
+# This is useful if the application would like to use the pubsub feature even when
+# the cluster global stable state is not OK. If the application wants to make sure only
+# one shard is serving a given channel, this feature should be kept as yes.
+#
+# cluster-allow-pubsubshard-when-down yes
+
 # Cluster link send buffer limit is the limit on the memory usage of an individual
 # cluster bus link's send buffer in bytes. Cluster links would be freed if they exceed
 # this limit. This is to primarily prevent send buffers from growing unbounded on links
diff --git a/src/acl.c b/src/acl.c
index 19e2a58f3..19b357c9e 100644
--- a/src/acl.c
+++ b/src/acl.c
@@ -1307,8 +1307,11 @@ int ACLCheckCommandPerm(const user *u, struct redisCommand *cmd, robj **argv, in
     }
 
     /* Check if the user can execute commands explicitly touching the keys
-     * mentioned in the command arguments. */
+     * mentioned in the command arguments. Shard channels are treated as
+     * special keys for client library to rely on `COMMAND` command
+     * to discover the node to connect to. These don't need acl key check. */
     if (!(u->flags & USER_FLAG_ALLKEYS) &&
+        !(cmd->flags & CMD_PUBSUB) &&
         (cmd->getkeys_proc || cmd->key_specs_num))
     {
         getKeysResult result = GETKEYS_RESULT_INIT;
@@ -1392,6 +1395,7 @@ void ACLKillPubsubClientsIfNeeded(user *u, list *upcoming) {
             }
             /* Check for channel violations. */
             if (!kill) {
+                /* Check for global channels violation. */
                 dictIterator *di = dictGetIterator(c->pubsub_channels);
                 dictEntry *de;                
                 while (!kill && ((de = dictNext(di)) != NULL)) {
@@ -1400,6 +1404,16 @@ void ACLKillPubsubClientsIfNeeded(user *u, list *upcoming) {
                             ACL_DENIED_CHANNEL);
                 }
                 dictReleaseIterator(di);
+
+                /* Check for shard channels violation. */
+                di = dictGetIterator(c->pubsubshard_channels);
+                while (!kill && ((de = dictNext(di)) != NULL)) {
+                    o = dictGetKey(de);
+                    kill = (ACLCheckPubsubChannelPerm(o->ptr,upcoming,0) ==
+                            ACL_DENIED_CHANNEL);
+                }
+
+                dictReleaseIterator(di);
             }
 
             /* Kill it. */
@@ -1448,9 +1462,9 @@ int ACLCheckAllUserCommandPerm(const user *u, struct redisCommand *cmd, robj **a
     int acl_retval = ACLCheckCommandPerm(u,cmd,argv,argc,idxptr);
     if (acl_retval != ACL_OK)
         return acl_retval;
-    if (cmd->proc == publishCommand)
+    if (cmd->proc == publishCommand || cmd->proc == spublishCommand)
         acl_retval = ACLCheckPubsubPerm(u,argv,1,1,0,idxptr);
-    else if (cmd->proc == subscribeCommand)
+    else if (cmd->proc == subscribeCommand || cmd->proc == ssubscribeCommand)
         acl_retval = ACLCheckPubsubPerm(u,argv,1,argc-1,0,idxptr);
     else if (cmd->proc == psubscribeCommand)
         acl_retval = ACLCheckPubsubPerm(u,argv,1,argc-1,1,idxptr);
diff --git a/src/cluster.c b/src/cluster.c
index 78e273f34..81322a8aa 100644
--- a/src/cluster.c
+++ b/src/cluster.c
@@ -57,6 +57,7 @@ void clusterUpdateState(void);
 int clusterNodeGetSlotBit(clusterNode *n, int slot);
 sds clusterGenNodesDescription(int filter, int use_pport);
 clusterNode *clusterLookupNode(const char *name);
+list *clusterGetNodesServingMySlots(clusterNode *node);
 int clusterNodeAddSlave(clusterNode *master, clusterNode *slave);
 int clusterAddSlot(clusterNode *n, int slot);
 int clusterDelSlot(int slot);
@@ -77,7 +78,9 @@ uint64_t clusterGetMaxEpoch(void);
 int clusterBumpConfigEpochWithoutConsensus(void);
 void moduleCallClusterReceivers(const char *sender_id, uint64_t module_id, uint8_t type, const unsigned char *payload, uint32_t len);
 const char *clusterGetMessageTypeString(int type);
+void removeChannelsInSlot(unsigned int slot);
 unsigned int countKeysInSlot(unsigned int hashslot);
+unsigned int countChannelsInSlot(unsigned int hashslot);
 unsigned int delKeysInSlot(unsigned int hashslot);
 
 /* Links to the next and previous entries for keys in the same slot are stored
@@ -631,6 +634,9 @@ void clusterInit(void) {
     /* Initialize data for the Slot to key API. */
     slotToKeyInit(server.db);
 
+    /* The slots -> channels map is a radix tree. Initialize it here. */
+    server.cluster->slots_to_channels = raxNew();
+
     /* Set myself->port/cport/pport to my listening ports, we'll just need to
      * discover the IP address via MEET messages. */
     deriveAnnouncedPorts(&myself->port, &myself->pport, &myself->cport);
@@ -1146,6 +1152,17 @@ clusterNode *clusterLookupNode(const char *name) {
     return dictGetVal(de);
 }
 
+/* Get all the nodes serving the same slots as myself. */
+list *clusterGetNodesServingMySlots(clusterNode *node) {
+    list *nodes_for_slot = listCreate();
+    clusterNode *my_primary = nodeIsMaster(node) ? node : node->slaveof;
+    listAddNodeTail(nodes_for_slot, my_primary);
+    for (int i=0; i < my_primary->numslaves; i++) {
+        listAddNodeTail(nodes_for_slot, my_primary->slaves[i]);
+    }
+    return nodes_for_slot;
+}
+
 /* This is only used after the handshake. When we connect a given IP/PORT
  * as a result of CLUSTER MEET we don't have the node name yet, so we
  * pick a random one, and will fix it when we receive the PONG request using
@@ -1921,7 +1938,7 @@ int clusterProcessPacket(clusterLink *link) {
 
         explen += sizeof(clusterMsgDataFail);
         if (totlen != explen) return 1;
-    } else if (type == CLUSTERMSG_TYPE_PUBLISH) {
+    } else if (type == CLUSTERMSG_TYPE_PUBLISH || type == CLUSTERMSG_TYPE_PUBLISHSHARD) {
         uint32_t explen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
 
         explen += sizeof(clusterMsgDataPublish) -
@@ -2278,7 +2295,7 @@ int clusterProcessPacket(clusterLink *link) {
                 "Ignoring FAIL message from unknown node %.40s about %.40s",
                 hdr->sender, hdr->data.fail.about.nodename);
         }
-    } else if (type == CLUSTERMSG_TYPE_PUBLISH) {
+    } else if (type == CLUSTERMSG_TYPE_PUBLISH || type == CLUSTERMSG_TYPE_PUBLISHSHARD) {
         if (!sender) return 1;  /* We don't know that node. */
 
         robj *channel, *message;
@@ -2286,8 +2303,10 @@ int clusterProcessPacket(clusterLink *link) {
 
         /* Don't bother creating useless objects if there are no
          * Pub/Sub subscribers. */
-        if (dictSize(server.pubsub_channels) ||
-           dictSize(server.pubsub_patterns))
+        if ((type == CLUSTERMSG_TYPE_PUBLISH
+            && serverPubsubSubscriptionCount() > 0)
+        || (type == CLUSTERMSG_TYPE_PUBLISHSHARD
+            && serverPubsubShardSubscriptionCount() > 0))
         {
             channel_len = ntohl(hdr->data.publish.msg.channel_len);
             message_len = ntohl(hdr->data.publish.msg.message_len);
@@ -2296,7 +2315,11 @@ int clusterProcessPacket(clusterLink *link) {
             message = createStringObject(
                         (char*)hdr->data.publish.msg.bulk_data+channel_len,
                         message_len);
-            pubsubPublishMessage(channel,message);
+            if (type == CLUSTERMSG_TYPE_PUBLISHSHARD) {
+                pubsubPublishMessageShard(channel, message);
+            } else {
+                pubsubPublishMessage(channel,message);
+            }
             decrRefCount(channel);
             decrRefCount(message);
         }
@@ -2841,7 +2864,7 @@ void clusterBroadcastPong(int target) {
  * the 'bulk_data', sanitizer generates an out-of-bounds error which is a false
  * positive in this context. */
 REDIS_NO_SANITIZE("bounds")
-void clusterSendPublish(clusterLink *link, robj *channel, robj *message) {
+void clusterSendPublish(clusterLink *link, robj *channel, robj *message, uint16_t type) {
     unsigned char *payload;
     clusterMsg buf[1];
     clusterMsg *hdr = (clusterMsg*) buf;
@@ -2853,7 +2876,7 @@ void clusterSendPublish(clusterLink *link, robj *channel, robj *message) {
     channel_len = sdslen(channel->ptr);
     message_len = sdslen(message->ptr);
 
-    clusterBuildMessageHdr(hdr,CLUSTERMSG_TYPE_PUBLISH);
+    clusterBuildMessageHdr(hdr,type);
     totlen = sizeof(clusterMsg)-sizeof(union clusterMsgData);
     totlen += sizeof(clusterMsgDataPublish) - 8 + channel_len + message_len;
 
@@ -2976,7 +2999,28 @@ int clusterSendModuleMessageToTarget(const char *target, uint64_t module_id, uin
  * messages to hosts without receives for a given channel.
  * -------------------------------------------------------------------------- */
 void clusterPropagatePublish(robj *channel, robj *message) {
-    clusterSendPublish(NULL, channel, message);
+    clusterSendPublish(NULL, channel, message, CLUSTERMSG_TYPE_PUBLISH);
+}
+
+/* -----------------------------------------------------------------------------
+ * CLUSTER Pub/Sub shard support
+ *
+ * Publish this message across the slot (primary/replica).
+ * -------------------------------------------------------------------------- */
+void clusterPropagatePublishShard(robj *channel, robj *message) {
+    list *nodes_for_slot = clusterGetNodesServingMySlots(server.cluster->myself);
+    if (listLength(nodes_for_slot) != 0) {
+        listIter li;
+        listNode *ln;
+        listRewind(nodes_for_slot, &li);
+        while((ln = listNext(&li))) {
+            clusterNode *node = listNodeValue(ln);
+            if (node != myself) {
+                clusterSendPublish(node->link, channel, message, CLUSTERMSG_TYPE_PUBLISHSHARD);
+            }
+        }
+    }
+    listRelease(nodes_for_slot);
 }
 
 /* -----------------------------------------------------------------------------
@@ -4075,6 +4119,14 @@ int clusterDelSlot(int slot) {
     clusterNode *n = server.cluster->slots[slot];
 
     if (!n) return C_ERR;
+
+    /* Cleanup the channels in master/replica as part of slot deletion. */
+    list *nodes_for_slot = clusterGetNodesServingMySlots(n);
+    listNode *ln = listSearchKey(nodes_for_slot, myself);
+    if (ln != NULL) {
+        removeChannelsInSlot(slot);
+    }
+    listRelease(nodes_for_slot);
     serverAssert(clusterNodeClearSlotBit(n,slot) == 1);
     server.cluster->slots[slot] = NULL;
     return C_OK;
@@ -4574,6 +4626,7 @@ const char *clusterGetMessageTypeString(int type) {
     case CLUSTERMSG_TYPE_MEET: return "meet";
     case CLUSTERMSG_TYPE_FAIL: return "fail";
     case CLUSTERMSG_TYPE_PUBLISH: return "publish";
+    case CLUSTERMSG_TYPE_PUBLISHSHARD: return "publishshard";
     case CLUSTERMSG_TYPE_FAILOVER_AUTH_REQUEST: return "auth-req";
     case CLUSTERMSG_TYPE_FAILOVER_AUTH_ACK: return "auth-ack";
     case CLUSTERMSG_TYPE_UPDATE: return "update";
@@ -5362,6 +5415,30 @@ NULL
     }
 }
 
+void removeChannelsInSlot(unsigned int slot) {
+    unsigned int channelcount = countChannelsInSlot(slot);
+    if (channelcount == 0) return;
+
+    /* Retrieve all the channels for the slot. */
+    robj **channels = zmalloc(sizeof(robj*)*channelcount);
+    raxIterator iter;
+    int j = 0;
+    unsigned char indexed[2];
+
+    indexed[0] = (slot >> 8) & 0xff;
+    indexed[1] = slot & 0xff;
+    raxStart(&iter,server.cluster->slots_to_channels);
+    raxSeek(&iter,">=",indexed,2);
+    while(raxNext(&iter)) {
+        if (iter.key[0] != indexed[0] || iter.key[1] != indexed[1]) break;
+        channels[j++] = createStringObject((char*)iter.key + 2, iter.key_len - 2);
+    }
+    raxStop(&iter);
+
+    pubsubUnsubscribeShardChannels(channels, channelcount);
+    zfree(channels);
+}
+
 /* -----------------------------------------------------------------------------
  * DUMP, RESTORE and MIGRATE commands
  * -------------------------------------------------------------------------- */
@@ -6121,6 +6198,10 @@ clusterNode *getNodeByQuery(client *c, struct redisCommand *cmd, robj **argv, in
         mc.cmd = cmd;
     }
 
+    int is_pubsubshard = cmd->proc == ssubscribeCommand ||
+            cmd->proc == sunsubscribeCommand ||
+            cmd->proc == spublishCommand;
+
     /* Check that all the keys are in the same hash slot, and obtain this
      * slot and the node associated. */
     for (i = 0; i < ms->count; i++) {
@@ -6172,8 +6253,8 @@ clusterNode *getNodeByQuery(client *c, struct redisCommand *cmd, robj **argv, in
                     importing_slot = 1;
                 }
             } else {
-                /* If it is not the first key, make sure it is exactly
-                 * the same key as the first we saw. */
+                /* If it is not the first key/channel, make sure it is exactly
+                 * the same key/channel as the first we saw. */
                 if (!equalStringObjects(firstkey,thiskey)) {
                     if (slot != thisslot) {
                         /* Error: multiple keys from different slots. */
@@ -6183,15 +6264,20 @@ clusterNode *getNodeByQuery(client *c, struct redisCommand *cmd, robj **argv, in
                         return NULL;
                     } else {
                         /* Flag this request as one with multiple different
-                         * keys. */
+                         * keys/channels. */
                         multiple_keys = 1;
                     }
                 }
             }
 
-            /* Migrating / Importing slot? Count keys we don't have. */
+            /* Migrating / Importing slot? Count keys we don't have.
+             * If it is pubsubshard command, it isn't required to check
+             * the channel being present or not in the node during the
+             * slot migration, the channel will be served from the source
+             * node until the migration completes with CLUSTER SETSLOT <slot>
+             * NODE <node-id>. */
             int flags = LOOKUP_NOTOUCH | LOOKUP_NOSTATS | LOOKUP_NONOTIFY;
-            if ((migrating_slot || importing_slot) &&
+            if ((migrating_slot || importing_slot) && !is_pubsubshard &&
                 lookupKeyReadWithFlags(&server.db[0], thiskey, flags) == NULL)
             {
                 missing_keys++;
@@ -6207,7 +6293,12 @@ clusterNode *getNodeByQuery(client *c, struct redisCommand *cmd, robj **argv, in
     /* Cluster is globally down but we got keys? We only serve the request
      * if it is a read command and when allow_reads_when_down is enabled. */
     if (server.cluster->state != CLUSTER_OK) {
-        if (!server.cluster_allow_reads_when_down) {
+        if (is_pubsubshard) {
+            if (!server.cluster_allow_pubsubshard_when_down) {
+                if (error_code) *error_code = CLUSTER_REDIR_DOWN_STATE;
+                return NULL;
+            }
+        } else if (!server.cluster_allow_reads_when_down) {
             /* The cluster is configured to block commands when the
              * cluster is down. */
             if (error_code) *error_code = CLUSTER_REDIR_DOWN_STATE;
@@ -6259,7 +6350,7 @@ clusterNode *getNodeByQuery(client *c, struct redisCommand *cmd, robj **argv, in
      * is serving, we can reply without redirection. */
     int is_write_command = (c->cmd->flags & CMD_WRITE) ||
                            (c->cmd->proc == execCommand && (c->mstate.cmd_flags & CMD_WRITE));
-    if (c->flags & CLIENT_READONLY &&
+    if (((c->flags & CLIENT_READONLY) || is_pubsubshard) &&
         !is_write_command &&
         nodeIsSlave(myself) &&
         myself->slaveof == n)
@@ -6482,3 +6573,51 @@ unsigned int delKeysInSlot(unsigned int hashslot) {
 unsigned int countKeysInSlot(unsigned int hashslot) {
     return (*server.db->slots_to_keys).by_slot[hashslot].count;
 }
+
+/* -----------------------------------------------------------------------------
+ * Operation(s) on channel rax tree.
+ * -------------------------------------------------------------------------- */
+
+void slotToChannelUpdate(sds channel, int add) {
+    size_t keylen = sdslen(channel);
+    unsigned int hashslot = keyHashSlot(channel,keylen);
+    unsigned char buf[64];
+    unsigned char *indexed = buf;
+
+    if (keylen+2 > 64) indexed = zmalloc(keylen+2);
+    indexed[0] = (hashslot >> 8) & 0xff;
+    indexed[1] = hashslot & 0xff;
+    memcpy(indexed+2,channel,keylen);
+    if (add) {
+        raxInsert(server.cluster->slots_to_channels,indexed,keylen+2,NULL,NULL);
+    } else {
+        raxRemove(server.cluster->slots_to_channels,indexed,keylen+2,NULL);
+    }
+    if (indexed != buf) zfree(indexed);
+}
+
+void slotToChannelAdd(sds channel) {
+    slotToChannelUpdate(channel,1);
+}
+
+void slotToChannelDel(sds channel) {
+    slotToChannelUpdate(channel,0);
+}
+
+/* Get the count of the channels for a given slot. */
+unsigned int countChannelsInSlot(unsigned int hashslot) {
+    raxIterator iter;
+    int j = 0;
+    unsigned char indexed[2];
+
+    indexed[0] = (hashslot >> 8) & 0xff;
+    indexed[1] = hashslot & 0xff;
+    raxStart(&iter,server.cluster->slots_to_channels);
+    raxSeek(&iter,">=",indexed,2);
+    while(raxNext(&iter)) {
+        if (iter.key[0] != indexed[0] || iter.key[1] != indexed[1]) break;
+        j++;
+    }
+    raxStop(&iter);
+    return j;
+}
diff --git a/src/cluster.h b/src/cluster.h
index d64e2a5b9..a28176e4b 100644
--- a/src/cluster.h
+++ b/src/cluster.h
@@ -97,6 +97,7 @@ typedef struct clusterLink {
 #define CLUSTERMSG_TYPE_MFSTART 8       /* Pause clients for manual failover */
 #define CLUSTERMSG_TYPE_MODULE 9        /* Module cluster API message. */
 #define CLUSTERMSG_TYPE_COUNT 10        /* Total number of message types. */
+#define CLUSTERMSG_TYPE_PUBLISHSHARD 11 /* Pub/Sub Publish shard propagation */
 
 /* Flags that a module can set in order to prevent certain Redis Cluster
  * features to be enabled. Useful when implementing a different distributed
@@ -173,6 +174,7 @@ typedef struct clusterState {
     clusterNode *migrating_slots_to[CLUSTER_SLOTS];
     clusterNode *importing_slots_from[CLUSTER_SLOTS];
     clusterNode *slots[CLUSTER_SLOTS];
+    rax *slots_to_channels;
     /* The following fields are used to take the slave state on elections. */
     mstime_t failover_auth_time; /* Time of previous or next election. */
     int failover_auth_count;    /* Number of votes received so far. */
@@ -320,6 +322,7 @@ int verifyClusterConfigWithData(void);
 unsigned long getClusterConnectionsCount(void);
 int clusterSendModuleMessageToTarget(const char *target, uint64_t module_id, uint8_t type, unsigned char *payload, uint32_t len);
 void clusterPropagatePublish(robj *channel, robj *message);
+void clusterPropagatePublishShard(robj *channel, robj *message);
 unsigned int keyHashSlot(char *key, int keylen);
 void slotToKeyAddEntry(dictEntry *entry, redisDb *db);
 void slotToKeyDelEntry(dictEntry *entry, redisDb *db);
@@ -329,5 +332,7 @@ void slotToKeyFlush(redisDb *db);
 void slotToKeyDestroy(redisDb *db);
 void clusterUpdateMyselfFlags(void);
 void clusterUpdateMyselfIp(void);
+void slotToChannelAdd(sds channel);
+void slotToChannelDel(sds channel);
 
 #endif /* __CLUSTER_H */
diff --git a/src/commands.c b/src/commands.c
index bf0537b4f..6e1a511ca 100644
--- a/src/commands.c
+++ b/src/commands.c
@@ -2913,12 +2913,36 @@ struct redisCommandArg PUBSUB_NUMSUB_Args[] = {
 {0}
 };
 
+/********** PUBSUB SHARDCHANNELS ********************/
+
+/* PUBSUB SHARDCHANNELS history */
+#define PUBSUB_SHARDCHANNELS_History NULL
+
+/* PUBSUB SHARDCHANNELS hints */
+#define PUBSUB_SHARDCHANNELS_Hints NULL
+
+/* PUBSUB SHARDCHANNELS argument table */
+struct redisCommandArg PUBSUB_SHARDCHANNELS_Args[] = {
+{"pattern",ARG_TYPE_STRING,-1,NULL,NULL,NULL,CMD_ARG_OPTIONAL},
+{0}
+};
+
+/********** PUBSUB SHARDNUMSUB ********************/
+
+/* PUBSUB SHARDNUMSUB history */
+#define PUBSUB_SHARDNUMSUB_History NULL
+
+/* PUBSUB SHARDNUMSUB hints */
+#define PUBSUB_SHARDNUMSUB_Hints NULL
+
 /* PUBSUB command table */
 struct redisCommand PUBSUB_Subcommands[] = {
 {"channels","List active channels","O(N) where N is the number of active channels, and assuming constant time pattern matching (relatively short channels and patterns)","2.8.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_PUBSUB,PUBSUB_CHANNELS_History,PUBSUB_CHANNELS_Hints,pubsubCommand,-2,CMD_PUBSUB|CMD_LOADING|CMD_STALE,0,.args=PUBSUB_CHANNELS_Args},
 {"help","Show helpful text about the different subcommands","O(1)","6.2.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_PUBSUB,PUBSUB_HELP_History,PUBSUB_HELP_Hints,pubsubCommand,2,CMD_LOADING|CMD_STALE,0},
 {"numpat","Get the count of unique patterns pattern subscriptions","O(1)","2.8.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_PUBSUB,PUBSUB_NUMPAT_History,PUBSUB_NUMPAT_Hints,pubsubCommand,2,CMD_PUBSUB|CMD_LOADING|CMD_STALE,0},
 {"numsub","Get the count of subscribers for channels","O(N) for the NUMSUB subcommand, where N is the number of requested channels","2.8.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_PUBSUB,PUBSUB_NUMSUB_History,PUBSUB_NUMSUB_Hints,pubsubCommand,-2,CMD_PUBSUB|CMD_LOADING|CMD_STALE,0,.args=PUBSUB_NUMSUB_Args},
+{"shardchannels","List active shard channels","O(N) where N is the number of active shard channels, and assuming constant time pattern matching (relatively short channels).","7.0.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_PUBSUB,PUBSUB_SHARDCHANNELS_History,PUBSUB_SHARDCHANNELS_Hints,pubsubCommand,-2,CMD_PUBSUB|CMD_LOADING|CMD_STALE,0,.args=PUBSUB_SHARDCHANNELS_Args},
+{"shardnumsub","Get the count of subscribers for shard channels","O(N) for the SHARDNUMSUB subcommand, where N is the number of requested channels","7.0.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_PUBSUB,PUBSUB_SHARDNUMSUB_History,PUBSUB_SHARDNUMSUB_Hints,pubsubCommand,-2,CMD_PUBSUB|CMD_LOADING|CMD_STALE,0},
 {0}
 };
 
@@ -2944,6 +2968,35 @@ struct redisCommandArg PUNSUBSCRIBE_Args[] = {
 {0}
 };
 
+/********** SPUBLISH ********************/
+
+/* SPUBLISH history */
+#define SPUBLISH_History NULL
+
+/* SPUBLISH hints */
+#define SPUBLISH_Hints NULL
+
+/* SPUBLISH argument table */
+struct redisCommandArg SPUBLISH_Args[] = {
+{"channel",ARG_TYPE_STRING,-1,NULL,NULL,NULL,CMD_ARG_NONE},
+{"message",ARG_TYPE_STRING,-1,NULL,NULL,NULL,CMD_ARG_NONE},
+{0}
+};
+
+/********** SSUBSCRIBE ********************/
+
+/* SSUBSCRIBE history */
+#define SSUBSCRIBE_History NULL
+
+/* SSUBSCRIBE hints */
+#define SSUBSCRIBE_Hints NULL
+
+/* SSUBSCRIBE argument table */
+struct redisCommandArg SSUBSCRIBE_Args[] = {
+{"channel",ARG_TYPE_STRING,-1,NULL,NULL,NULL,CMD_ARG_MULTIPLE},
+{0}
+};
+
 /********** SUBSCRIBE ********************/
 
 /* SUBSCRIBE history */
@@ -2961,6 +3014,20 @@ struct redisCommandArg SUBSCRIBE_Args[] = {
 {0}
 };
 
+/********** SUNSUBSCRIBE ********************/
+
+/* SUNSUBSCRIBE history */
+#define SUNSUBSCRIBE_History NULL
+
+/* SUNSUBSCRIBE hints */
+#define SUNSUBSCRIBE_Hints NULL
+
+/* SUNSUBSCRIBE argument table */
+struct redisCommandArg SUNSUBSCRIBE_Args[] = {
+{"channel",ARG_TYPE_STRING,-1,NULL,NULL,NULL,CMD_ARG_OPTIONAL|CMD_ARG_MULTIPLE},
+{0}
+};
+
 /********** UNSUBSCRIBE ********************/
 
 /* UNSUBSCRIBE history */
@@ -6511,7 +6578,10 @@ struct redisCommand redisCommandTable[] = {
 {"publish","Post a message to a channel","O(N+M) where N is the number of clients subscribed to the receiving channel and M is the total number of subscribed patterns (by any client).","2.0.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_PUBSUB,PUBLISH_History,PUBLISH_Hints,publishCommand,3,CMD_PUBSUB|CMD_LOADING|CMD_STALE|CMD_FAST|CMD_MAY_REPLICATE|CMD_SENTINEL,0,.args=PUBLISH_Args},
 {"pubsub","A container for Pub/Sun commands","Depends on subcommand.","2.8.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_PUBSUB,PUBSUB_History,PUBSUB_Hints,NULL,-2,0,0,.subcommands=PUBSUB_Subcommands},
 {"punsubscribe","Stop listening for messages posted to channels matching the given patterns","O(N+M) where N is the number of patterns the client is already subscribed and M is the number of total patterns subscribed in the system (by any client).","2.0.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_PUBSUB,PUNSUBSCRIBE_History,PUNSUBSCRIBE_Hints,punsubscribeCommand,-1,CMD_PUBSUB|CMD_NOSCRIPT|CMD_LOADING|CMD_STALE|CMD_SENTINEL,0,.args=PUNSUBSCRIBE_Args},
+{"spublish","Post a message to a shard channel","O(N) where N is the number of clients subscribed to the receiving shard channel.","7.0.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_PUBSUB,SPUBLISH_History,SPUBLISH_Hints,spublishCommand,3,CMD_PUBSUB|CMD_LOADING|CMD_STALE|CMD_FAST|CMD_MAY_REPLICATE,0,{{CMD_KEY_SHARD_CHANNEL,KSPEC_BS_INDEX,.bs.index={1},KSPEC_FK_RANGE,.fk.range={0,1,0}}},.args=SPUBLISH_Args},
+{"ssubscribe","Listen for messages published to the given shard channels","O(N) where N is the number of shard channels to subscribe to.","7.0.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_PUBSUB,SSUBSCRIBE_History,SSUBSCRIBE_Hints,ssubscribeCommand,-2,CMD_PUBSUB|CMD_NOSCRIPT|CMD_LOADING|CMD_STALE,0,{{CMD_KEY_SHARD_CHANNEL,KSPEC_BS_INDEX,.bs.index={1},KSPEC_FK_RANGE,.fk.range={-1,1,0}}},.args=SSUBSCRIBE_Args},
 {"subscribe","Listen for messages published to the given channels","O(N) where N is the number of channels to subscribe to.","2.0.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_PUBSUB,SUBSCRIBE_History,SUBSCRIBE_Hints,subscribeCommand,-2,CMD_PUBSUB|CMD_NOSCRIPT|CMD_LOADING|CMD_STALE|CMD_SENTINEL,0,.args=SUBSCRIBE_Args},
+{"sunsubscribe","Stop listening for messages posted to the given shard channels","O(N) where N is the number of clients already subscribed to a channel.","7.0.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_PUBSUB,SUNSUBSCRIBE_History,SUNSUBSCRIBE_Hints,sunsubscribeCommand,-1,CMD_PUBSUB|CMD_NOSCRIPT|CMD_LOADING|CMD_STALE,0,{{CMD_KEY_SHARD_CHANNEL,KSPEC_BS_INDEX,.bs.index={1},KSPEC_FK_RANGE,.fk.range={-1,1,0}}},.args=SUNSUBSCRIBE_Args},
 {"unsubscribe","Stop listening for messages posted to the given channels","O(N) where N is the number of clients already subscribed to a channel.","2.0.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_PUBSUB,UNSUBSCRIBE_History,UNSUBSCRIBE_Hints,unsubscribeCommand,-1,CMD_PUBSUB|CMD_NOSCRIPT|CMD_LOADING|CMD_STALE|CMD_SENTINEL,0,.args=UNSUBSCRIBE_Args},
 /* scripting */
 {"eval","Execute a Lua script server side","Depends on the script that is executed.","2.6.0",CMD_DOC_NONE,NULL,NULL,COMMAND_GROUP_SCRIPTING,EVAL_History,EVAL_Hints,evalCommand,-3,CMD_NOSCRIPT|CMD_SKIP_MONITOR|CMD_MAY_REPLICATE|CMD_NO_MANDATORY_KEYS,ACL_CATEGORY_SCRIPTING,{{CMD_KEY_WRITE|CMD_KEY_READ,KSPEC_BS_INDEX,.bs.index={2},KSPEC_FK_KEYNUM,.fk.keynum={0,1,1}}},evalGetKeys,.args=EVAL_Args},
diff --git a/src/commands/pubsub-shardchannels.json b/src/commands/pubsub-shardchannels.json
new file mode 100644
index 000000000..450cd8dcd
--- /dev/null
+++ b/src/commands/pubsub-shardchannels.json
@@ -0,0 +1,23 @@
+{
+  "SHARDCHANNELS": {
+    "summary": "List active shard channels",
+    "complexity": "O(N) where N is the number of active shard channels, and assuming constant time pattern matching (relatively short channels).",
+    "group": "pubsub",
+    "since": "7.0.0",
+    "arity": -2,
+    "container": "PUBSUB",
+    "function": "pubsubCommand",
+    "command_flags": [
+      "PUBSUB",
+      "LOADING",
+      "STALE"
+    ],
+    "arguments": [
+      {
+        "name": "pattern",
+        "type": "string",
+        "optional": true
+      }
+    ]
+  }
+}
diff --git a/src/commands/pubsub-shardnumsub.json b/src/commands/pubsub-shardnumsub.json
new file mode 100644
index 000000000..167132b31
--- /dev/null
+++ b/src/commands/pubsub-shardnumsub.json
@@ -0,0 +1,16 @@
+{
+  "SHARDNUMSUB": {
+    "summary": "Get the count of subscribers for shard channels",
+    "complexity": "O(N) for the SHARDNUMSUB subcommand, where N is the number of requested channels",
+    "group": "pubsub",
+    "since": "7.0.0",
+    "arity": -2,
+    "container": "PUBSUB",
+    "function": "pubsubCommand",
+    "command_flags": [
+      "PUBSUB",
+      "LOADING",
+      "STALE"
+    ]
+  }
+}
diff --git a/src/commands/spublish.json b/src/commands/spublish.json
new file mode 100644
index 000000000..34835b9dc
--- /dev/null
+++ b/src/commands/spublish.json
@@ -0,0 +1,46 @@
+{
+  "SPUBLISH": {
+    "summary": "Post a message to a shard channel",
+    "complexity": "O(N) where N is the number of clients subscribed to the receiving shard channel.",
+    "group": "pubsub",
+    "since": "7.0.0",
+    "arity": 3,
+    "function": "spublishCommand",
+    "command_flags": [
+      "PUBSUB",
+      "LOADING",
+      "STALE",
+      "FAST",
+      "MAY_REPLICATE"
+    ],
+    "arguments": [
+      {
+        "name": "channel",
+        "type": "string"
+      },
+      {
+        "name": "message",
+        "type": "string"
+      }
+    ],
+    "key_specs": [
+      {
+        "flags": [
+          "SHARD_CHANNEL"
+        ],
+        "begin_search": {
+          "index": {
+            "pos": 1
+          }
+        },
+        "find_keys": {
+          "range": {
+            "lastkey": 0,
+            "step": 1,
+            "limit": 0
+          }
+        }
+      }
+    ]
+  }
+}
diff --git a/src/commands/ssubscribe.json b/src/commands/ssubscribe.json
new file mode 100644
index 000000000..541e4aac0
--- /dev/null
+++ b/src/commands/ssubscribe.json
@@ -0,0 +1,42 @@
+{
+  "SSUBSCRIBE": {
+    "summary": "Listen for messages published to the given shard channels",
+    "complexity": "O(N) where N is the number of shard channels to subscribe to.",
+    "group": "pubsub",
+    "since": "7.0.0",
+    "arity": -2,
+    "function": "ssubscribeCommand",
+    "command_flags": [
+      "PUBSUB",
+      "NOSCRIPT",
+      "LOADING",
+      "STALE"
+    ],
+    "arguments": [
+      {
+        "name": "channel",
+        "type": "string",
+        "multiple": true
+      }
+    ],
+    "key_specs": [
+      {
+        "flags": [
+          "SHARD_CHANNEL"
+        ],
+        "begin_search": {
+          "index": {
+            "pos": 1
+          }
+        },
+        "find_keys": {
+          "range": {
+            "lastkey": -1,
+            "step": 1,
+            "limit": 0
+          }
+        }
+      }
+    ]
+  }
+}
diff --git a/src/commands/sunsubscribe.json b/src/commands/sunsubscribe.json
new file mode 100644
index 000000000..ba43a02b6
--- /dev/null
+++ b/src/commands/sunsubscribe.json
@@ -0,0 +1,43 @@
+{
+  "SUNSUBSCRIBE": {
+    "summary": "Stop listening for messages posted to the given shard channels",
+    "complexity": "O(N) where N is the number of clients already subscribed to a channel.",
+    "group": "pubsub",
+    "since": "7.0.0",
+    "arity": -1,
+    "function": "sunsubscribeCommand",
+    "command_flags": [
+      "PUBSUB",
+      "NOSCRIPT",
+      "LOADING",
+      "STALE"
+    ],
+    "arguments": [
+      {
+        "name": "channel",
+        "type": "string",
+        "optional": true,
+        "multiple": true
+      }
+    ],
+    "key_specs": [
+      {
+        "flags": [
+          "SHARD_CHANNEL"
+        ],
+        "begin_search": {
+          "index": {
+            "pos": 1
+          }
+        },
+        "find_keys": {
+          "range": {
+            "lastkey": -1,
+            "step": 1,
+            "limit": 0
+          }
+        }
+      }
+    ]
+  }
+}
diff --git a/src/config.c b/src/config.c
index 03b6af29a..317b92ea2 100644
--- a/src/config.c
+++ b/src/config.c
@@ -2636,6 +2636,7 @@ standardConfig configs[] = {
     createBoolConfig("cluster-enabled", NULL, IMMUTABLE_CONFIG, server.cluster_enabled, 0, NULL, NULL),
     createBoolConfig("appendonly", NULL, MODIFIABLE_CONFIG | DENY_LOADING_CONFIG, server.aof_enabled, 0, NULL, updateAppendonly),
     createBoolConfig("cluster-allow-reads-when-down", NULL, MODIFIABLE_CONFIG, server.cluster_allow_reads_when_down, 0, NULL, NULL),
+    createBoolConfig("cluster-allow-pubsubshard-when-down", NULL, MODIFIABLE_CONFIG, server.cluster_allow_pubsubshard_when_down, 1, NULL, NULL),
     createBoolConfig("crash-log-enabled", NULL, MODIFIABLE_CONFIG, server.crashlog_enabled, 1, NULL, updateSighandlerEnabled),
     createBoolConfig("crash-memcheck-enabled", NULL, MODIFIABLE_CONFIG, server.memcheck_enabled, 1, NULL, NULL),
     createBoolConfig("use-exit-on-panic", NULL, MODIFIABLE_CONFIG | HIDDEN_CONFIG, server.use_exit_on_panic, 0, NULL, NULL),
diff --git a/src/module.c b/src/module.c
index 9cae23db5..58e3bb666 100644
--- a/src/module.c
+++ b/src/module.c
@@ -790,6 +790,7 @@ int64_t commandKeySpecsFlagsFromString(const char *s) {
         char *t = tokens[j];
         if (!strcasecmp(t,"write")) flags |= CMD_KEY_WRITE;
         else if (!strcasecmp(t,"read")) flags |= CMD_KEY_READ;
+        else if (!strcasecmp(t,"shard_channel")) flags |= CMD_KEY_SHARD_CHANNEL;
         else if (!strcasecmp(t,"incomplete")) flags |= CMD_KEY_INCOMPLETE;
         else break;
     }
diff --git a/src/networking.c b/src/networking.c
index 20d05a9e3..50c7d99ca 100644
--- a/src/networking.c
+++ b/src/networking.c
@@ -190,6 +190,7 @@ client *createClient(connection *conn) {
     c->watched_keys = listCreate();
     c->pubsub_channels = dictCreate(&objectKeyPointerValueDictType);
     c->pubsub_patterns = listCreate();
+    c->pubsubshard_channels = dictCreate(&objectKeyPointerValueDictType);
     c->peerid = NULL;
     c->sockname = NULL;
     c->client_list_node = NULL;
@@ -1424,9 +1425,11 @@ void freeClient(client *c) {
 
     /* Unsubscribe from all the pubsub channels */
     pubsubUnsubscribeAllChannels(c,0);
+    pubsubUnsubscribeShardAllChannels(c, 0);
     pubsubUnsubscribeAllPatterns(c,0);
     dictRelease(c->pubsub_channels);
     listRelease(c->pubsub_patterns);
+    dictRelease(c->pubsubshard_channels);
 
     /* Free data structures. */
     listRelease(c->reply);
@@ -2592,6 +2595,7 @@ void resetCommand(client *c) {
     discardTransaction(c);
 
     pubsubUnsubscribeAllChannels(c,0);
+    pubsubUnsubscribeShardAllChannels(c, 0);
     pubsubUnsubscribeAllPatterns(c,0);
 
     if (c->name) {
diff --git a/src/pubsub.c b/src/pubsub.c
index 6da5b18cf..e805b16ef 100644
--- a/src/pubsub.c
+++ b/src/pubsub.c
@@ -30,8 +30,68 @@
 #include "server.h"
 #include "cluster.h"
 
+/* Structure to hold the pubsub related metadata. Currently used
+ * for pubsub and pubsubshard feature. */
+typedef struct pubsubtype {
+    int shard;
+    dict *(*clientPubSubChannels)(client*);
+    int (*subscriptionCount)(client*);
+    dict **serverPubSubChannels;
+    robj **subscribeMsg;
+    robj **unsubscribeMsg;
+}pubsubtype;
+
+/*
+ * Get client's global Pub/Sub channels subscription count.
+ */
 int clientSubscriptionsCount(client *c);
 
+/*
+ * Get client's shard level Pub/Sub channels subscription count.
+ */
+int clientShardSubscriptionsCount(client *c);
+
+/*
+ * Get client's global Pub/Sub channels dict.
+ */
+dict* getClientPubSubChannels(client *c);
+
+/*
+ * Get client's shard level Pub/Sub channels dict.
+ */
+dict* getClientPubSubShardChannels(client *c);
+
+/*
+ * Get list of channels client is subscribed to.
+ * If a pattern is provided, the subset of channels is returned
+ * matching the pattern.
+ */
+void channelList(client *c, sds pat, dict* pubsub_channels);
+
+/*
+ * Pub/Sub type for global channels.
+ */
+pubsubtype pubSubType = {
+    .shard = 0,
+    .clientPubSubChannels = getClientPubSubChannels,
+    .subscriptionCount = clientSubscriptionsCount,
+    .serverPubSubChannels = &server.pubsub_channels,
+    .subscribeMsg = &shared.subscribebulk,
+    .unsubscribeMsg = &shared.unsubscribebulk,
+};
+
+/*
+ * Pub/Sub type for shard level channels bounded to a slot.
+ */
+pubsubtype pubSubShardType = {
+    .shard = 1,
+    .clientPubSubChannels = getClientPubSubShardChannels,
+    .subscriptionCount = clientShardSubscriptionsCount,
+    .serverPubSubChannels = &server.pubsubshard_channels,
+    .subscribeMsg = &shared.ssubscribebulk,
+    .unsubscribeMsg = &shared.sunsubscribebulk
+};
+
 /*-----------------------------------------------------------------------------
  * Pubsub client replies API
  *----------------------------------------------------------------------------*/
@@ -66,31 +126,31 @@ void addReplyPubsubPatMessage(client *c, robj *pat, robj *channel, robj *msg) {
 }
 
 /* Send the pubsub subscription notification to the client. */
-void addReplyPubsubSubscribed(client *c, robj *channel) {
+void addReplyPubsubSubscribed(client *c, robj *channel, pubsubtype type) {
     if (c->resp == 2)
         addReply(c,shared.mbulkhdr[3]);
     else
         addReplyPushLen(c,3);
-    addReply(c,shared.subscribebulk);
+    addReply(c,*type.subscribeMsg);
     addReplyBulk(c,channel);
-    addReplyLongLong(c,clientSubscriptionsCount(c));
+    addReplyLongLong(c,type.subscriptionCount(c));
 }
 
 /* Send the pubsub unsubscription notification to the client.
  * Channel can be NULL: this is useful when the client sends a mass
  * unsubscribe command but there are no channels to unsubscribe from: we
  * still send a notification. */
-void addReplyPubsubUnsubscribed(client *c, robj *channel) {
+void addReplyPubsubUnsubscribed(client *c, robj *channel, pubsubtype type) {
     if (c->resp == 2)
         addReply(c,shared.mbulkhdr[3]);
     else
         addReplyPushLen(c,3);
-    addReply(c,shared.unsubscribebulk);
+    addReply(c, *type.unsubscribeMsg);
     if (channel)
         addReplyBulk(c,channel);
     else
         addReplyNull(c);
-    addReplyLongLong(c,clientSubscriptionsCount(c));
+    addReplyLongLong(c,type.subscriptionCount(c));
 }
 
 /* Send the pubsub pattern subscription notification to the client. */
@@ -125,28 +185,57 @@ void addReplyPubsubPatUnsubscribed(client *c, robj *pattern) {
  * Pubsub low level API
  *----------------------------------------------------------------------------*/
 
+/* Return the number of pubsub channels + patterns is handled. */
+int serverPubsubSubscriptionCount() {
+    return dictSize(server.pubsub_channels) + dictSize(server.pubsub_patterns);
+}
+
+/* Return the number of pubsub shard level channels is handled. */
+int serverPubsubShardSubscriptionCount() {
+    return dictSize(server.pubsubshard_channels);
+}
+
+
 /* Return the number of channels + patterns a client is subscribed to. */
 int clientSubscriptionsCount(client *c) {
-    return dictSize(c->pubsub_channels)+
-           listLength(c->pubsub_patterns);
+    return dictSize(c->pubsub_channels) + listLength(c->pubsub_patterns);
+}
+
+/* Return the number of shard level channels a client is subscribed to. */
+int clientShardSubscriptionsCount(client *c) {
+    return dictSize(c->pubsubshard_channels);
+}
+
+dict* getClientPubSubChannels(client *c) {
+    return c->pubsub_channels;
+}
+
+dict* getClientPubSubShardChannels(client *c) {
+    return c->pubsubshard_channels;
+}
+
+/* Return the number of pubsub + pubsub shard level channels
+ * a client is subscribed to. */
+int clientTotalPubSubSubscriptionCount(client *c) {
+    return clientSubscriptionsCount(c) + clientShardSubscriptionsCount(c);
 }
 
 /* Subscribe a client to a channel. Returns 1 if the operation succeeded, or
  * 0 if the client was already subscribed to that channel. */
-int pubsubSubscribeChannel(client *c, robj *channel) {
+int pubsubSubscribeChannel(client *c, robj *channel, pubsubtype type) {
     dictEntry *de;
     list *clients = NULL;
     int retval = 0;
 
     /* Add the channel to the client -> channels hash table */
-    if (dictAdd(c->pubsub_channels,channel,NULL) == DICT_OK) {
+    if (dictAdd(type.clientPubSubChannels(c),channel,NULL) == DICT_OK) {
         retval = 1;
         incrRefCount(channel);
         /* Add the client to the channel -> list of clients hash table */
-        de = dictFind(server.pubsub_channels,channel);
+        de = dictFind(*type.serverPubSubChannels, channel);
         if (de == NULL) {
             clients = listCreate();
-            dictAdd(server.pubsub_channels,channel,clients);
+            dictAdd(*type.serverPubSubChannels, channel, clients);
             incrRefCount(channel);
         } else {
             clients = dictGetVal(de);
@@ -154,13 +243,13 @@ int pubsubSubscribeChannel(client *c, robj *channel) {
         listAddNodeTail(clients,c);
     }
     /* Notify the client */
-    addReplyPubsubSubscribed(c,channel);
+    addReplyPubsubSubscribed(c,channel,type);
     return retval;
 }
 
 /* Unsubscribe a client from a channel. Returns 1 if the operation succeeded, or
  * 0 if the client was not subscribed to the specified channel. */
-int pubsubUnsubscribeChannel(client *c, robj *channel, int notify) {
+int pubsubUnsubscribeChannel(client *c, robj *channel, int notify, pubsubtype type) {
     dictEntry *de;
     list *clients;
     listNode *ln;
@@ -169,10 +258,10 @@ int pubsubUnsubscribeChannel(client *c, robj *channel, int notify) {
     /* Remove the channel from the client -> channels hash table */
     incrRefCount(channel); /* channel may be just a pointer to the same object
                             we have in the hash tables. Protect it... */
-    if (dictDelete(c->pubsub_channels,channel) == DICT_OK) {
+    if (dictDelete(type.clientPubSubChannels(c),channel) == DICT_OK) {
         retval = 1;
         /* Remove the client from the channel -> clients list hash table */
-        de = dictFind(server.pubsub_channels,channel);
+        de = dictFind(*type.serverPubSubChannels, channel);
         serverAssertWithInfo(c,NULL,de != NULL);
         clients = dictGetVal(de);
         ln = listSearchKey(clients,c);
@@ -182,15 +271,53 @@ int pubsubUnsubscribeChannel(client *c, robj *channel, int notify) {
             /* Free the list and associated hash entry at all if this was
              * the latest client, so that it will be possible to abuse
              * Redis PUBSUB creating millions of channels. */
-            dictDelete(server.pubsub_channels,channel);
+            dictDelete(*type.serverPubSubChannels, channel);
+            /* As this channel isn't subscribed by anyone, it's safe
+             * to remove the channel from the slot. */
+            if (server.cluster_enabled & type.shard) {
+                slotToChannelDel(channel->ptr);
+            }
         }
     }
     /* Notify the client */
-    if (notify) addReplyPubsubUnsubscribed(c,channel);
+    if (notify) {
+        addReplyPubsubUnsubscribed(c,channel,type);
+    }
     decrRefCount(channel); /* it is finally safe to release it */
     return retval;
 }
 
+void pubsubShardUnsubscribeAllClients(robj *channel) {
+    int retval;
+    dictEntry *de = dictFind(server.pubsubshard_channels, channel);
+    serverAssertWithInfo(NULL,channel,de != NULL);
+    list *clients = dictGetVal(de);
+    if (listLength(clients) > 0) {
+        /* For each client subscribed to the channel, unsubscribe it. */
+        listIter li;
+        listNode *ln;
+        listRewind(clients, &li);
+        while ((ln = listNext(&li)) != NULL) {
+            client *c = listNodeValue(ln);
+            retval = dictDelete(c->pubsubshard_channels, channel);
+            serverAssertWithInfo(c,channel,retval == DICT_OK);
+            addReplyPubsubUnsubscribed(c, channel, pubSubShardType);
+            /* If the client has no other pubsub subscription,
+             * move out of pubsub mode. */
+            if (clientTotalPubSubSubscriptionCount(c) == 0) {
+                c->flags &= ~CLIENT_PUBSUB;
+            }
+        }
+    }
+    /* Delete the channel from server pubsubshard channels hash table. */
+    retval = dictDelete(server.pubsubshard_channels, channel);
+    /* Delete the channel from slots_to_channel mapping. */
+    slotToChannelDel(channel->ptr);
+    serverAssertWithInfo(NULL,channel,retval == DICT_OK);
+    decrRefCount(channel); /* it is finally safe to release it */
+}
+
+
 /* Subscribe a client to a pattern. Returns 1 if the operation succeeded, or 0 if the client was already subscribed to that pattern. */
 int pubsubSubscribePattern(client *c, robj *pattern) {
     dictEntry *de;
@@ -250,24 +377,53 @@ int pubsubUnsubscribePattern(client *c, robj *pattern, int notify) {
 
 /* Unsubscribe from all the channels. Return the number of channels the
  * client was subscribed to. */
-int pubsubUnsubscribeAllChannels(client *c, int notify) {
+int pubsubUnsubscribeAllChannelsInternal(client *c, int notify, pubsubtype type) {
     int count = 0;
-    if (dictSize(c->pubsub_channels) > 0) {
-        dictIterator *di = dictGetSafeIterator(c->pubsub_channels);
+    if (dictSize(type.clientPubSubChannels(c)) > 0) {
+        dictIterator *di = dictGetSafeIterator(type.clientPubSubChannels(c));
         dictEntry *de;
 
         while((de = dictNext(di)) != NULL) {
             robj *channel = dictGetKey(de);
 
-            count += pubsubUnsubscribeChannel(c,channel,notify);
+            count += pubsubUnsubscribeChannel(c,channel,notify,type);
         }
         dictReleaseIterator(di);
     }
     /* We were subscribed to nothing? Still reply to the client. */
-    if (notify && count == 0) addReplyPubsubUnsubscribed(c,NULL);
+    if (notify && count == 0) {
+        addReplyPubsubUnsubscribed(c,NULL,type);
+    }
     return count;
 }
 
+/*
+ * Unsubscribe a client from all global channels.
+ */
+int pubsubUnsubscribeAllChannels(client *c, int notify) {
+    int count = pubsubUnsubscribeAllChannelsInternal(c,notify,pubSubType);
+    return count;
+}
+
+/*
+ * Unsubscribe a client from all shard subscribed channels.
+ */
+int pubsubUnsubscribeShardAllChannels(client *c, int notify) {
+    int count = pubsubUnsubscribeAllChannelsInternal(c, notify, pubSubShardType);
+    return count;
+}
+
+/*
+ * Unsubscribe a client from provided shard subscribed channel(s).
+ */
+void pubsubUnsubscribeShardChannels(robj **channels, unsigned int count) {
+    for (unsigned int j = 0; j < count; j++) {
+        /* Remove the channel from server and from the clients
+         * subscribed to it as well as notify them. */
+        pubsubShardUnsubscribeAllClients(channels[j]);
+    }
+}
+
 /* Unsubscribe from all the patterns. Return the number of patterns the
  * client was subscribed from. */
 int pubsubUnsubscribeAllPatterns(client *c, int notify) {
@@ -285,8 +441,10 @@ int pubsubUnsubscribeAllPatterns(client *c, int notify) {
     return count;
 }
 
-/* Publish a message */
-int pubsubPublishMessage(robj *channel, robj *message) {
+/*
+ * Publish a message to all the subscribers.
+ */
+int pubsubPublishMessageInternal(robj *channel, robj *message, pubsubtype type) {
     int receivers = 0;
     dictEntry *de;
     dictIterator *di;
@@ -294,7 +452,7 @@ int pubsubPublishMessage(robj *channel, robj *message) {
     listIter li;
 
     /* Send to clients listening for that channel */
-    de = dictFind(server.pubsub_channels,channel);
+    de = dictFind(*type.serverPubSubChannels, channel);
     if (de) {
         list *list = dictGetVal(de);
         listNode *ln;
@@ -308,6 +466,12 @@ int pubsubPublishMessage(robj *channel, robj *message) {
             receivers++;
         }
     }
+
+    if (type.shard) {
+        /* Shard pubsub ignores patterns. */
+        return receivers;
+    }
+
     /* Send to clients listening to matching channels */
     di = dictGetIterator(server.pubsub_patterns);
     if (di) {
@@ -334,6 +498,17 @@ int pubsubPublishMessage(robj *channel, robj *message) {
     return receivers;
 }
 
+/* Publish a message to all the subscribers. */
+int pubsubPublishMessage(robj *channel, robj *message) {
+    return pubsubPublishMessageInternal(channel,message,pubSubType);
+}
+
+/* Publish a shard message to all the subscribers. */
+int pubsubPublishMessageShard(robj *channel, robj *message) {
+    return pubsubPublishMessageInternal(channel, message, pubSubShardType);
+}
+
+
 /*-----------------------------------------------------------------------------
  * Pubsub commands implementation
  *----------------------------------------------------------------------------*/
@@ -352,13 +527,12 @@ void subscribeCommand(client *c) {
         addReplyError(c, "SUBSCRIBE isn't allowed for a DENY BLOCKING client");
         return;
     }
-
     for (j = 1; j < c->argc; j++)
-        pubsubSubscribeChannel(c,c->argv[j]);
+        pubsubSubscribeChannel(c,c->argv[j],pubSubType);
     c->flags |= CLIENT_PUBSUB;
 }
 
-/* UNSUBSCRIBE [channel [channel ...]] */
+/* UNSUBSCRIBE [channel ...] */
 void unsubscribeCommand(client *c) {
     if (c->argc == 1) {
         pubsubUnsubscribeAllChannels(c,1);
@@ -366,9 +540,9 @@ void unsubscribeCommand(client *c) {
         int j;
 
         for (j = 1; j < c->argc; j++)
-            pubsubUnsubscribeChannel(c,c->argv[j],1);
+            pubsubUnsubscribeChannel(c,c->argv[j],1,pubSubType);
     }
-    if (clientSubscriptionsCount(c) == 0) c->flags &= ~CLIENT_PUBSUB;
+    if (clientTotalPubSubSubscriptionCount(c) == 0) c->flags &= ~CLIENT_PUBSUB;
 }
 
 /* PSUBSCRIBE pattern [pattern ...] */
@@ -401,7 +575,7 @@ void punsubscribeCommand(client *c) {
         for (j = 1; j < c->argc; j++)
             pubsubUnsubscribePattern(c,c->argv[j],1);
     }
-    if (clientSubscriptionsCount(c) == 0) c->flags &= ~CLIENT_PUBSUB;
+    if (clientTotalPubSubSubscriptionCount(c) == 0) c->flags &= ~CLIENT_PUBSUB;
 }
 
 /* PUBLISH <channel> <message> */
@@ -429,7 +603,11 @@ void pubsubCommand(client *c) {
 "    Return number of subscriptions to patterns.",
 "NUMSUB [<channel> ...]",
 "    Return the number of subscribers for the specified channels, excluding",
-"    pattern subscriptions(default: no channels).",
+"    pattern subscriptions(default: no channels)."
+"SHARDCHANNELS [<pattern>]",
+"    Return the currently active shard level channels matching a <pattern> (default: '*').",
+"SHARDNUMSUB [<channel> ...]",
+"    Return the number of subscribers for the specified shard level channel(s)",
 NULL
         };
         addReplyHelp(c, help);
@@ -438,25 +616,7 @@ NULL
     {
         /* PUBSUB CHANNELS [<pattern>] */
         sds pat = (c->argc == 2) ? NULL : c->argv[2]->ptr;
-        dictIterator *di = dictGetIterator(server.pubsub_channels);
-        dictEntry *de;
-        long mblen = 0;
-        void *replylen;
-
-        replylen = addReplyDeferredLen(c);
-        while((de = dictNext(di)) != NULL) {
-            robj *cobj = dictGetKey(de);
-            sds channel = cobj->ptr;
-
-            if (!pat || stringmatchlen(pat, sdslen(pat),
-                                       channel, sdslen(channel),0))
-            {
-                addReplyBulk(c,cobj);
-                mblen++;
-            }
-        }
-        dictReleaseIterator(di);
-        setDeferredArrayLen(c,replylen,mblen);
+        channelList(c, pat, server.pubsub_channels);
     } else if (!strcasecmp(c->argv[1]->ptr,"numsub") && c->argc >= 2) {
         /* PUBSUB NUMSUB [Channel_1 ... Channel_N] */
         int j;
@@ -471,7 +631,93 @@ NULL
     } else if (!strcasecmp(c->argv[1]->ptr,"numpat") && c->argc == 2) {
         /* PUBSUB NUMPAT */
         addReplyLongLong(c,dictSize(server.pubsub_patterns));
+    } else if (!strcasecmp(c->argv[1]->ptr,"shardchannels") &&
+        (c->argc == 2 || c->argc == 3)) 
+    {
+        /* PUBSUB SHARDCHANNELS */
+        sds pat = (c->argc == 2) ? NULL : c->argv[2]->ptr;
+        channelList(c,pat,server.pubsubshard_channels);
+    } else if (!strcasecmp(c->argv[1]->ptr,"shardnumsub") && c->argc >= 2) {
+        /* PUBSUB SHARDNUMSUB [Channel_1 ... Channel_N] */
+        int j;
+
+        addReplyArrayLen(c, (c->argc-2)*2);
+        for (j = 2; j < c->argc; j++) {
+            list *l = dictFetchValue(server.pubsubshard_channels, c->argv[j]);
+
+            addReplyBulk(c,c->argv[j]);
+            addReplyLongLong(c,l ? listLength(l) : 0);
+        }
     } else {
         addReplySubcommandSyntaxError(c);
     }
 }
+
+void channelList(client *c, sds pat, dict *pubsub_channels) {
+    dictIterator *di = dictGetIterator(pubsub_channels);
+    dictEntry *de;
+    long mblen = 0;
+    void *replylen;
+
+    replylen = addReplyDeferredLen(c);
+    while((de = dictNext(di)) != NULL) {
+        robj *cobj = dictGetKey(de);
+        sds channel = cobj->ptr;
+
+        if (!pat || stringmatchlen(pat, sdslen(pat),
+                                   channel, sdslen(channel),0))
+        {
+            addReplyBulk(c,cobj);
+            mblen++;
+        }
+    }
+    dictReleaseIterator(di);
+    setDeferredArrayLen(c,replylen,mblen);
+}
+
+/* SPUBLISH <channel> <message> */
+void spublishCommand(client *c) {
+    int receivers = pubsubPublishMessageInternal(c->argv[1], c->argv[2], pubSubShardType);
+    if (server.cluster_enabled) {
+        clusterPropagatePublishShard(c->argv[1], c->argv[2]);
+    } else {
+        forceCommandPropagation(c,PROPAGATE_REPL);
+    }
+    addReplyLongLong(c,receivers);
+}
+
+/* SSUBSCRIBE channel [channel ...] */
+void ssubscribeCommand(client *c) {
+    if (c->flags & CLIENT_DENY_BLOCKING) {
+        /* A client that has CLIENT_DENY_BLOCKING flag on
+         * expect a reply per command and so can not execute subscribe. */
+        addReplyError(c, "SSUBSCRIBE isn't allowed for a DENY BLOCKING client");
+        return;
+    }
+
+    for (int j = 1; j < c->argc; j++) {
+        /* A channel is only considered to be added, if a
+         * subscriber exists for it. And if a subscriber
+         * already exists the slotToChannel doesn't needs
+         * to be incremented. */
+        if (server.cluster_enabled &
+            (dictFind(*pubSubShardType.serverPubSubChannels, c->argv[j]) == NULL)) {
+            slotToChannelAdd(c->argv[j]->ptr);
+        }
+        pubsubSubscribeChannel(c, c->argv[j], pubSubShardType);
+    }
+    c->flags |= CLIENT_PUBSUB;
+}
+
+
+/* SUNSUBSCRIBE [channel ...] */
+void sunsubscribeCommand(client *c) {
+    if (c->argc == 1) {
+        pubsubUnsubscribeShardAllChannels(c, 1);
+    } else {
+        for (int j = 1; j < c->argc; j++) {
+            pubsubUnsubscribeChannel(c, c->argv[j], 1, pubSubShardType);
+        }
+    }
+    if (clientTotalPubSubSubscriptionCount(c) == 0) c->flags &= ~CLIENT_PUBSUB;
+}
diff --git a/src/redis-cli.c b/src/redis-cli.c
index 397e3bfa8..94697f99f 100644
--- a/src/redis-cli.c
+++ b/src/redis-cli.c
@@ -1381,7 +1381,8 @@ static int cliSendCommand(int argc, char **argv, long repeat) {
     if (!strcasecmp(command,"shutdown")) config.shutdown = 1;
     if (!strcasecmp(command,"monitor")) config.monitor_mode = 1;
     if (!strcasecmp(command,"subscribe") ||
-        !strcasecmp(command,"psubscribe")) config.pubsub_mode = 1;
+        !strcasecmp(command,"psubscribe") ||
+        !strcasecmp(command,"ssubscribe")) config.pubsub_mode = 1;
     if (!strcasecmp(command,"sync") ||
         !strcasecmp(command,"psync")) config.slave_mode = 1;
 
diff --git a/src/server.c b/src/server.c
index e7cf5740b..4770a5df0 100644
--- a/src/server.c
+++ b/src/server.c
@@ -1648,6 +1648,8 @@ void createSharedObjects(void) {
     shared.pmessagebulk = createStringObject("$8\r\npmessage\r\n",14);
     shared.subscribebulk = createStringObject("$9\r\nsubscribe\r\n",15);
     shared.unsubscribebulk = createStringObject("$11\r\nunsubscribe\r\n",18);
+    shared.ssubscribebulk = createStringObject("$10\r\nssubscribe\r\n", 17);
+    shared.sunsubscribebulk = createStringObject("$12\r\nsunsubscribe\r\n", 19);
     shared.psubscribebulk = createStringObject("$10\r\npsubscribe\r\n",17);
     shared.punsubscribebulk = createStringObject("$12\r\npunsubscribe\r\n",19);
 
@@ -2367,6 +2369,7 @@ void initServer(void) {
     evictionPoolAlloc(); /* Initialize the LRU keys pool. */
     server.pubsub_channels = dictCreate(&keylistDictType);
     server.pubsub_patterns = dictCreate(&keylistDictType);
+    server.pubsubshard_channels = dictCreate(&keylistDictType);
     server.cronloops = 0;
     server.in_script = 0;
     server.in_exec = 0;
@@ -3499,14 +3502,16 @@ int processCommand(client *c) {
     if ((c->flags & CLIENT_PUBSUB && c->resp == 2) &&
         c->cmd->proc != pingCommand &&
         c->cmd->proc != subscribeCommand &&
+        c->cmd->proc != ssubscribeCommand &&
         c->cmd->proc != unsubscribeCommand &&
+        c->cmd->proc != sunsubscribeCommand &&
         c->cmd->proc != psubscribeCommand &&
         c->cmd->proc != punsubscribeCommand &&
         c->cmd->proc != quitCommand &&
         c->cmd->proc != resetCommand) {
         rejectCommandFormat(c,
-            "Can't execute '%s': only (P)SUBSCRIBE / "
-            "(P)UNSUBSCRIBE / PING / QUIT / RESET are allowed in this context",
+            "Can't execute '%s': only (P|S)SUBSCRIBE / "
+            "(P|S)UNSUBSCRIBE / PING / QUIT / RESET are allowed in this context",
             c->cmd->name);
         return C_OK;
     }
@@ -4001,6 +4006,7 @@ void addReplyFlagsForKeyArgs(client *c, uint64_t flags) {
     void *flaglen = addReplyDeferredLen(c);
     flagcount += addReplyCommandFlag(c,flags,CMD_KEY_WRITE, "write");
     flagcount += addReplyCommandFlag(c,flags,CMD_KEY_READ, "read");
+    flagcount += addReplyCommandFlag(c,flags,CMD_KEY_SHARD_CHANNEL, "shard_channel");
     flagcount += addReplyCommandFlag(c,flags,CMD_KEY_INCOMPLETE, "incomplete");
     setDeferredSetLen(c, flaglen, flagcount);
 }
diff --git a/src/server.h b/src/server.h
index 792eb30a1..c1a0af355 100644
--- a/src/server.h
+++ b/src/server.h
@@ -233,9 +233,12 @@ extern int configOOMScoreAdjValuesDefaults[CONFIG_OOM_COUNT];
 
 /* Key argument flags. Please check the command table defined in the server.c file
  * for more information about the meaning of every flag. */
-#define CMD_KEY_WRITE (1ULL<<0)
-#define CMD_KEY_READ (1ULL<<1)
-#define CMD_KEY_INCOMPLETE (1ULL<<2)   /* meaning that the keyspec might not point out to all keys it should cover */
+#define CMD_KEY_WRITE (1ULL<<0)             /* "write" flag */
+#define CMD_KEY_READ (1ULL<<1)              /* "read" flag */
+#define CMD_KEY_SHARD_CHANNEL (1ULL<<2)     /* "shard_channel" flag */
+#define CMD_KEY_INCOMPLETE (1ULL<<3)        /* "incomplete" flag (meaning that
+                                             * the keyspec might not point out
+                                             * to all keys it should cover) */
 
 /* AOF states */
 #define AOF_OFF 0             /* AOF is off */
@@ -1086,6 +1089,7 @@ typedef struct client {
     list *watched_keys;     /* Keys WATCHED for MULTI/EXEC CAS */
     dict *pubsub_channels;  /* channels a client is interested in (SUBSCRIBE) */
     list *pubsub_patterns;  /* patterns a client is interested in (SUBSCRIBE) */
+    dict *pubsubshard_channels;  /* shard level channels a client is interested in (SSUBSCRIBE) */
     sds peerid;             /* Cached peer ID. */
     sds sockname;           /* Cached connection target address. */
     listNode *client_list_node; /* list node in client list */
@@ -1174,6 +1178,7 @@ struct sharedObjectsStruct {
     *time, *pxat, *absttl, *retrycount, *force, *justid, 
     *lastid, *ping, *setid, *keepttl, *load, *createconsumer,
     *getack, *special_asterick, *special_equals, *default_username, *redacted,
+    *ssubscribebulk,*sunsubscribebulk,
     *select[PROTO_SHARED_SELECT_CMDS],
     *integers[OBJ_SHARED_INTEGERS],
     *mbulkhdr[OBJ_SHARED_BULKHDR_LEN], /* "*<value>\r\n" */
@@ -1751,6 +1756,7 @@ struct redisServer {
     dict *pubsub_patterns;  /* A dict of pubsub_patterns */
     int notify_keyspace_events; /* Events to propagate via Pub/Sub. This is an
                                    xor of NOTIFY_... flags. */
+    dict *pubsubshard_channels;  /* Map channels to list of subscribed clients */
     /* Cluster */
     int cluster_enabled;      /* Is cluster enabled? */
     int cluster_port;         /* Set the cluster port for a node. */
@@ -1821,6 +1827,8 @@ struct redisServer {
                                 * failover then any replica can be used. */
     int target_replica_port; /* Failover target port */
     int failover_state; /* Failover state */
+    int cluster_allow_pubsubshard_when_down; /* Is pubsubshard allowed when the cluster
+                                                is down, doesn't affect pubsub global. */
 };
 
 #define MAX_KEYS_BUFFER 256
@@ -2816,9 +2824,14 @@ robj *hashTypeDup(robj *o);
 
 /* Pub / Sub */
 int pubsubUnsubscribeAllChannels(client *c, int notify);
+int pubsubUnsubscribeShardAllChannels(client *c, int notify);
+void pubsubUnsubscribeShardChannels(robj **channels, unsigned int count);
 int pubsubUnsubscribeAllPatterns(client *c, int notify);
 int pubsubPublishMessage(robj *channel, robj *message);
+int pubsubPublishMessageShard(robj *channel, robj *message);
 void addReplyPubsubMessage(client *c, robj *channel, robj *msg);
+int serverPubsubSubscriptionCount();
+int serverPubsubShardSubscriptionCount();
 
 /* Keyspace events notification */
 void notifyKeyspaceEvent(int type, char *event, robj *key, int dbid);
@@ -2902,6 +2915,7 @@ void freeReplicationBacklogRefMemAsync(list *blocks, rax *index);
 /* API to get key arguments from commands */
 int *getKeysPrepareResult(getKeysResult *result, int numkeys);
 int getKeysFromCommand(struct redisCommand *cmd, robj **argv, int argc, getKeysResult *result);
+int getChannelsFromCommand(struct redisCommand *cmd, int argc, getKeysResult *result);
 void getKeysFreeResult(getKeysResult *result);
 int sintercardGetKeys(struct redisCommand *cmd,robj **argv, int argc, getKeysResult *result);
 int zunionInterDiffGetKeys(struct redisCommand *cmd,robj **argv, int argc, getKeysResult *result);
@@ -3184,6 +3198,9 @@ void psubscribeCommand(client *c);
 void punsubscribeCommand(client *c);
 void publishCommand(client *c);
 void pubsubCommand(client *c);
+void spublishCommand(client *c);
+void ssubscribeCommand(client *c);
+void sunsubscribeCommand(client *c);
 void watchCommand(client *c);
 void unwatchCommand(client *c);
 void clusterCommand(client *c);
diff --git a/src/tracking.c b/src/tracking.c
index 11e2587e2..bb36f742d 100644
--- a/src/tracking.c
+++ b/src/tracking.c
@@ -228,6 +228,12 @@ void trackingRememberKeys(client *c) {
         getKeysFreeResult(&result);
         return;
     }
+    /* Shard channels are treated as special keys for client
+     * library to rely on `COMMAND` command to discover the node
+     * to connect to. These channels doesn't need to be tracked. */
+    if (c->cmd->flags & CMD_PUBSUB) {
+        return;
+    }
 
     int *keys = result.keys;
 
diff --git a/tests/cluster/cluster.tcl b/tests/cluster/cluster.tcl
index 7b7ce5343..31e0c3667 100644
--- a/tests/cluster/cluster.tcl
+++ b/tests/cluster/cluster.tcl
@@ -66,7 +66,7 @@ proc s {n field} {
     get_info_field [R $n info] $field
 }
 
-# Assuming nodes are reest, this function performs slots allocation.
+# Assuming nodes are reset, this function performs slots allocation.
 # Only the first 'n' nodes are used.
 proc cluster_allocate_slots {n} {
     set slot 16383
@@ -129,6 +129,32 @@ proc create_cluster {masters slaves} {
     set ::cluster_replica_nodes $slaves
 }
 
+proc cluster_allocate_with_continuous_slots {n} {
+    set slot 16383
+    set avg [expr ($slot+1) / $n]
+    while {$slot >= 0} {
+        set node [expr $slot/$avg >= $n ? $n-1 : $slot/$avg]
+        lappend slots_$node $slot
+        incr slot -1
+    }
+    for {set j 0} {$j < $n} {incr j} {
+        R $j cluster addslots {*}[set slots_${j}]
+    }
+}
+
+# Create a cluster composed of the specified number of masters and slaves with continuous slots.
+proc cluster_create_with_continuous_slots {masters slaves} {
+    cluster_allocate_with_continuous_slots $masters
+    if {$slaves} {
+        cluster_allocate_slaves $masters $slaves
+    }
+    assert_cluster_state ok
+
+    set ::cluster_master_nodes $masters
+    set ::cluster_replica_nodes $slaves
+}
+
+
 # Set the cluster node-timeout to all the reachalbe nodes.
 proc set_cluster_node_timeout {to} {
     foreach_redis_id id {
@@ -243,4 +269,4 @@ proc get_link_from_peer {this_instance_id peer_nodename} {
         }
     }
     return {}
-}
+}
\ No newline at end of file
diff --git a/tests/cluster/tests/19-cluster-nodes-slots.tcl b/tests/cluster/tests/19-cluster-nodes-slots.tcl
index 80f68d5d0..77faec912 100644
--- a/tests/cluster/tests/19-cluster-nodes-slots.tcl
+++ b/tests/cluster/tests/19-cluster-nodes-slots.tcl
@@ -2,27 +2,6 @@
 
 source "../tests/includes/init-tests.tcl"
 
-proc cluster_allocate_with_continuous_slots {n} {
-    set slot 16383
-    set avg [expr ($slot+1) / $n]
-    while {$slot >= 0} {
-        set node [expr $slot/$avg >= $n ? $n-1 : $slot/$avg]
-        lappend slots_$node $slot
-        incr slot -1
-    }
-    for {set j 0} {$j < $n} {incr j} {
-        R $j cluster addslots {*}[set slots_${j}]
-    }
-}
-
-proc cluster_create_with_continuous_slots {masters slaves} {
-    cluster_allocate_with_continuous_slots $masters
-    if {$slaves} {
-        cluster_allocate_slaves $masters $slaves
-    }
-    assert_cluster_state ok
-}
-
 test "Create a 2 nodes cluster" {
     cluster_create_with_continuous_slots 2 2
 }
diff --git a/tests/cluster/tests/23-multiple-slot-operations.tcl b/tests/cluster/tests/23-multiple-slot-operations.tcl
index 906033c72..965ecd5af 100644
--- a/tests/cluster/tests/23-multiple-slot-operations.tcl
+++ b/tests/cluster/tests/23-multiple-slot-operations.tcl
@@ -2,7 +2,7 @@
 
 source "../tests/includes/init-tests.tcl"
 
-proc cluster_allocate_with_continuous_slots {n} {
+proc cluster_allocate_with_continuous_slots_local {n} {
     R 0 cluster ADDSLOTSRANGE 0 3276
     R 1 cluster ADDSLOTSRANGE 3277 6552
     R 2 cluster ADDSLOTSRANGE 6553 9828
@@ -10,8 +10,8 @@ proc cluster_allocate_with_continuous_slots {n} {
     R 4 cluster ADDSLOTSRANGE 13105 16383
 }
 
-proc cluster_create_with_continuous_slots {masters slaves} {
-    cluster_allocate_with_continuous_slots $masters
+proc cluster_create_with_continuous_slots_local {masters slaves} {
+    cluster_allocate_with_continuous_slots_local $masters
     if {$slaves} {
         cluster_allocate_slaves $masters $slaves
     }
@@ -20,7 +20,7 @@ proc cluster_create_with_continuous_slots {masters slaves} {
 
 
 test "Create a 5 nodes cluster" {
-    cluster_create_with_continuous_slots 5 5
+    cluster_create_with_continuous_slots_local 5 5
 }
 
 test "Cluster should start ok" {
diff --git a/tests/cluster/tests/25-pubsubshard-slot-migration.tcl b/tests/cluster/tests/25-pubsubshard-slot-migration.tcl
new file mode 100644
index 000000000..11b77d36a
--- /dev/null
+++ b/tests/cluster/tests/25-pubsubshard-slot-migration.tcl
@@ -0,0 +1,171 @@
+source "../tests/includes/init-tests.tcl"
+
+test "Create a 3 nodes cluster" {
+    cluster_create_with_continuous_slots 3 3
+}
+
+test "Cluster is up" {
+    assert_cluster_state ok
+}
+
+set cluster [redis_cluster 127.0.0.1:[get_instance_attrib redis 0 port]]
+
+test "Migrate a slot, verify client receives sunsubscribe on primary serving the slot." {
+
+    # Setup the to and from node
+    set channelname mychannel
+    set slot [$cluster cluster keyslot $channelname]
+    array set nodefrom [$cluster masternode_for_slot $slot]
+    array set nodeto [$cluster masternode_notfor_slot $slot]
+
+    set subscribeclient [redis_deferring_client_by_addr $nodefrom(host) $nodefrom(port)]
+
+    $subscribeclient deferred 1
+    $subscribeclient ssubscribe $channelname
+    $subscribeclient read
+
+    assert_equal {OK} [$nodefrom(link) cluster setslot $slot migrating $nodeto(id)]
+    assert_equal {OK} [$nodeto(link) cluster setslot $slot importing $nodefrom(id)]
+
+    # Verify subscribe is still valid, able to receive messages.
+    $nodefrom(link) spublish $channelname hello
+    assert_equal {message mychannel hello} [$subscribeclient read]
+
+    assert_equal {OK} [$nodefrom(link) cluster setslot $slot node $nodeto(id)]
+   
+    set msg [$subscribeclient read]
+    assert {"sunsubscribe" eq [lindex $msg 0]}
+    assert {$channelname eq [lindex $msg 1]}
+    assert {"0" eq [lindex $msg 2]}
+
+    assert_equal {OK} [$nodeto(link) cluster setslot $slot node $nodeto(id)]
+
+    $subscribeclient close
+}
+
+test "Client subscribes to multiple channels, migrate a slot, verify client receives sunsubscribe on primary serving the slot." {
+
+    # Setup the to and from node
+    set channelname ch3
+    set anotherchannelname ch7
+    set slot [$cluster cluster keyslot $channelname]
+    array set nodefrom [$cluster masternode_for_slot $slot]
+    array set nodeto [$cluster masternode_notfor_slot $slot]
+
+    set subscribeclient [redis_deferring_client_by_addr $nodefrom(host) $nodefrom(port)]
+
+    $subscribeclient deferred 1
+    $subscribeclient ssubscribe $channelname
+    $subscribeclient read
+
+    $subscribeclient ssubscribe $anotherchannelname
+    $subscribeclient read
+
+    assert_equal {OK} [$nodefrom(link) cluster setslot $slot migrating $nodeto(id)]
+    assert_equal {OK} [$nodeto(link) cluster setslot $slot importing $nodefrom(id)]
+
+    # Verify subscribe is still valid, able to receive messages.
+    $nodefrom(link) spublish $channelname hello
+    assert_equal {message ch3 hello} [$subscribeclient read]
+
+    assert_equal {OK} [$nodefrom(link) cluster setslot $slot node $nodeto(id)]
+
+    # Verify the client receives sunsubscribe message for the channel(slot) which got migrated.
+    set msg [$subscribeclient read]
+    assert {"sunsubscribe" eq [lindex $msg 0]}
+    assert {$channelname eq [lindex $msg 1]}
+    assert {"1" eq [lindex $msg 2]}
+
+    assert_equal {OK} [$nodeto(link) cluster setslot $slot node $nodeto(id)]
+
+    $nodefrom(link) spublish $anotherchannelname hello
+
+    # Verify the client is still connected and receives message from the other channel.
+    set msg [$subscribeclient read]
+    assert {"message" eq [lindex $msg 0]}
+    assert {$anotherchannelname eq [lindex $msg 1]}
+    assert {"hello" eq [lindex $msg 2]}
+
+    $subscribeclient close
+}
+
+test "Migrate a slot, verify client receives sunsubscribe on replica serving the slot." {
+
+    # Setup the to and from node
+    set channelname mychannel1
+    set slot [$cluster cluster keyslot $channelname]
+    array set nodefrom [$cluster masternode_for_slot $slot]
+    array set nodeto [$cluster masternode_notfor_slot $slot]
+
+    # Get replica node serving slot (mychannel) to connect a client.
+    set replicanodeinfo [$cluster cluster replicas $nodefrom(id)]
+    set args [split $replicanodeinfo " "]
+    set addr [lindex [split [lindex $args 1] @] 0]
+    set replicahost [lindex [split $addr :] 0]
+    set replicaport [lindex [split $addr :] 1]
+    set subscribeclient [redis_deferring_client_by_addr $replicahost $replicaport]
+
+    $subscribeclient deferred 1
+    $subscribeclient ssubscribe $channelname
+    $subscribeclient read
+
+    assert_equal {OK} [$nodefrom(link) cluster setslot $slot migrating $nodeto(id)]
+    assert_equal {OK} [$nodeto(link) cluster setslot $slot importing $nodefrom(id)]
+
+    # Verify subscribe is still valid, able to receive messages.
+    $nodefrom(link) spublish $channelname hello
+    assert_equal {message mychannel1 hello} [$subscribeclient read]
+
+    assert_equal {OK} [$nodefrom(link) cluster setslot $slot node $nodeto(id)]
+    assert_equal {OK} [$nodeto(link) cluster setslot $slot node $nodeto(id)]
+
+    set msg [$subscribeclient read]
+    assert {"sunsubscribe" eq [lindex $msg 0]}
+    assert {$channelname eq [lindex $msg 1]}
+    assert {"0" eq [lindex $msg 2]}
+
+    $subscribeclient close
+}
+
+test "Delete a slot, verify sunsubscribe message" {
+    set channelname ch2
+    set slot [$cluster cluster keyslot $channelname]
+
+    array set primary_client [$cluster masternode_for_slot $slot]
+
+    set subscribeclient [redis_deferring_client_by_addr $primary_client(host) $primary_client(port)]
+    $subscribeclient deferred 1
+    $subscribeclient ssubscribe $channelname
+    $subscribeclient read
+
+    $primary_client(link) cluster DELSLOTS $slot
+
+    set msg [$subscribeclient read]
+    assert {"sunsubscribe" eq [lindex $msg 0]}
+    assert {$channelname eq [lindex $msg 1]}
+    assert {"0" eq [lindex $msg 2]}
+    
+    $subscribeclient close
+}
+
+test "Reset cluster, verify sunsubscribe message" {
+    set channelname ch4
+    set slot [$cluster cluster keyslot $channelname]
+
+    array set primary_client [$cluster masternode_for_slot $slot]
+
+    set subscribeclient [redis_deferring_client_by_addr $primary_client(host) $primary_client(port)]
+    $subscribeclient deferred 1
+    $subscribeclient ssubscribe $channelname
+    $subscribeclient read
+
+    $cluster cluster reset HARD
+
+    set msg [$subscribeclient read]
+    assert {"sunsubscribe" eq [lindex $msg 0]}
+    assert {$channelname eq [lindex $msg 1]}
+    assert {"0" eq [lindex $msg 2]}
+    
+    $cluster close
+    $subscribeclient close
+}
\ No newline at end of file
diff --git a/tests/cluster/tests/26-pubsubshard.tcl b/tests/cluster/tests/26-pubsubshard.tcl
new file mode 100644
index 000000000..2619eda0a
--- /dev/null
+++ b/tests/cluster/tests/26-pubsubshard.tcl
@@ -0,0 +1,94 @@
+# Test PUBSUB shard propagation in a cluster slot.
+
+source "../tests/includes/init-tests.tcl"
+
+test "Create a 3 nodes cluster" {
+    cluster_create_with_continuous_slots 3 3
+}
+
+set cluster [redis_cluster 127.0.0.1:[get_instance_attrib redis 0 port]]
+test "Pub/Sub shard basics" {
+
+    set slot [$cluster cluster keyslot "channel.0"]
+    array set publishnode [$cluster masternode_for_slot $slot]
+    array set notshardnode [$cluster masternode_notfor_slot $slot]
+
+    set publishclient [redis_client_by_addr $publishnode(host) $publishnode(port)]
+    set subscribeclient [redis_deferring_client_by_addr $publishnode(host) $publishnode(port)]
+    set subscribeclient2 [redis_deferring_client_by_addr $publishnode(host) $publishnode(port)]
+    set anotherclient [redis_deferring_client_by_addr $notshardnode(host) $notshardnode(port)]
+
+    $subscribeclient ssubscribe channel.0
+    $subscribeclient read
+
+    $subscribeclient2 ssubscribe channel.0
+    $subscribeclient2 read
+
+    $anotherclient ssubscribe channel.0
+    catch {$anotherclient read} err
+    assert_match {MOVED *} $err
+
+    set data [randomValue]
+    $publishclient spublish channel.0 $data
+
+    set msg [$subscribeclient read]
+    assert_equal $data [lindex $msg 2]
+
+    set msg [$subscribeclient2 read]
+    assert_equal $data [lindex $msg 2]
+
+    $publishclient close
+    $subscribeclient close
+    $subscribeclient2 close
+    $anotherclient close
+}
+
+test "client can't subscribe to multiple shard channels across different slots in same call" {
+    catch {$cluster ssubscribe channel.0 channel.1} err
+    assert_match {CROSSSLOT Keys*} $err
+}
+
+test "client can subscribe to multiple shard channels across different slots in separate call" {
+    $cluster ssubscribe ch3
+    $cluster ssubscribe ch7
+
+    $cluster sunsubscribe ch3
+    $cluster sunsubscribe ch7
+}
+
+
+test "Verify Pub/Sub and Pub/Sub shard no overlap" {
+    set slot [$cluster cluster keyslot "channel.0"]
+    array set publishnode [$cluster masternode_for_slot $slot]
+    array set notshardnode [$cluster masternode_notfor_slot $slot]
+
+    set publishshardclient [redis_client_by_addr $publishnode(host) $publishnode(port)]
+    set publishclient [redis_deferring_client_by_addr $publishnode(host) $publishnode(port)]
+    set subscribeshardclient [redis_deferring_client_by_addr $publishnode(host) $publishnode(port)]
+    set subscribeclient [redis_deferring_client_by_addr $publishnode(host) $publishnode(port)]
+
+    $subscribeshardclient deferred 1
+    $subscribeshardclient ssubscribe channel.0
+    $subscribeshardclient read
+
+    $subscribeclient deferred 1
+    $subscribeclient subscribe channel.0
+    $subscribeclient read
+
+    set sharddata "testingpubsubdata"
+    $publishshardclient spublish channel.0 $sharddata
+
+    set data "somemoredata"
+    $publishclient publish channel.0 $data
+
+    set msg [$subscribeshardclient read]
+    assert_equal $sharddata [lindex $msg 2]
+
+    set msg [$subscribeclient read]
+    assert_equal $data [lindex $msg 2]
+
+    $cluster close
+    $publishclient close
+    $subscribeclient close
+    $subscribeshardclient close
+}
\ No newline at end of file
diff --git a/tests/instances.tcl b/tests/instances.tcl
index 2a3336b78..52e61418e 100644
--- a/tests/instances.tcl
+++ b/tests/instances.tcl
@@ -677,9 +677,19 @@ proc redis_deferring_client {type id} {
     return $client
 }
 
+proc redis_deferring_client_by_addr {host port} {
+    set client [redis $host $port 1 $::tls]
+    return $client
+}
+
 proc redis_client {type id} {
     set port [get_instance_attrib $type $id port]
     set host [get_instance_attrib $type $id host]
     set client [redis $host $port 0 $::tls]
     return $client
 }
+
+proc redis_client_by_addr {host port} {
+    set client [redis $host $port 0 $::tls]
+    return $client
+}
\ No newline at end of file
diff --git a/tests/support/cluster.tcl b/tests/support/cluster.tcl
index df4b7f3d0..081ef6a95 100644
--- a/tests/support/cluster.tcl
+++ b/tests/support/cluster.tcl
@@ -13,6 +13,7 @@ package require Tcl 8.5
 package provide redis_cluster 0.1
 
 namespace eval redis_cluster {}
+set ::redis_cluster::internal_id 0
 set ::redis_cluster::id 0
 array set ::redis_cluster::startup_nodes {}
 array set ::redis_cluster::nodes {}
@@ -32,7 +33,8 @@ set ::redis_cluster::plain_commands {
     hget hmset hmget hincrby hincrbyfloat hdel hlen hkeys hvals
     hgetall hexists hscan incrby decrby incrbyfloat getset move
     expire expireat pexpire pexpireat type ttl pttl persist restore
-    dump bitcount bitpos pfadd pfcount
+    dump bitcount bitpos pfadd pfcount cluster ssubscribe spublish
+    sunsubscribe
 }
 
 # Create a cluster client. The nodes are given as a list of host:port. The TLS
@@ -118,6 +120,7 @@ proc ::redis_cluster::__method__refresh_nodes_map {id} {
         # Build this node description as an hash.
         set node [dict create \
             id $nodeid \
+            internal_id $id \
             addr $addr \
             host $host \
             port $port \
@@ -265,6 +268,7 @@ proc ::redis_cluster::get_keys_from_command {cmd argv} {
         mget {return $argv}
         eval {return [lrange $argv 2 1+[lindex $argv 1]]}
         evalsha {return [lrange $argv 2 1+[lindex $argv 1]]}
+        spublish {return [list [lindex $argv 1]]}
     }
 
     # All the remaining commands are not handled.
diff --git a/tests/test_helper.tcl b/tests/test_helper.tcl
index 722b04ed0..d47e83c56 100644
--- a/tests/test_helper.tcl
+++ b/tests/test_helper.tcl
@@ -62,6 +62,7 @@ set ::all_tests {
     integration/redis-benchmark
     integration/dismiss-mem
     unit/pubsub
+    unit/pubsubshard
     unit/slowlog
     unit/scripting
     unit/functions
diff --git a/tests/unit/acl.tcl b/tests/unit/acl.tcl
index 03a3ba926..660e841fb 100644
--- a/tests/unit/acl.tcl
+++ b/tests/unit/acl.tcl
@@ -87,6 +87,10 @@ start_server {tags {"acl external:skip"}} {
         r PUBLISH foo bar
     } {0}
 
+    test {By default users are able to publish to any shard channel} {
+        r SPUBLISH foo bar
+    } {0}
+
     test {By default users are able to subscribe to any channel} {
         set rd [redis_deferring_client]
         $rd AUTH psuser pspass
@@ -96,6 +100,15 @@ start_server {tags {"acl external:skip"}} {
         $rd close
     } {0}
 
+    test {By default users are able to subscribe to any shard channel} {
+        set rd [redis_deferring_client]
+        $rd AUTH psuser pspass
+        $rd read
+        $rd SSUBSCRIBE foo
+        assert_match {ssubscribe foo 1} [$rd read]
+        $rd close
+    } {0}
+
     test {By default users are able to subscribe to any pattern} {
         set rd [redis_deferring_client]
         $rd AUTH psuser pspass
@@ -113,6 +126,14 @@ start_server {tags {"acl external:skip"}} {
         set e
     } {*NOPERM*channel*}
 
+    test {It's possible to allow publishing to a subset of shard channels} {
+        r ACL setuser psuser resetchannels &foo:1 &bar:*
+        assert_equal {0} [r SPUBLISH foo:1 somemessage]
+        assert_equal {0} [r SPUBLISH bar:2 anothermessage]
+        catch {r SPUBLISH zap:3 nosuchmessage} e
+        set e
+    } {*NOPERM*channel*}
+
     test {Validate subset of channels is prefixed with resetchannels flag} {
         r ACL setuser hpuser on nopass resetchannels &foo +@all
 
@@ -166,6 +187,19 @@ start_server {tags {"acl external:skip"}} {
         set e
     } {*NOPERM*channel*}
 
+    test {It's possible to allow subscribing to a subset of shard channels} {
+        set rd [redis_deferring_client]
+        $rd AUTH psuser pspass
+        $rd read
+        $rd SSUBSCRIBE foo:1
+        assert_match {ssubscribe foo:1 1} [$rd read]
+        $rd SSUBSCRIBE bar:2
+        assert_match {ssubscribe bar:2 2} [$rd read]
+        $rd SSUBSCRIBE zap:3
+        catch {$rd read} e
+        set e
+    } {*NOPERM*channel*}
+
     test {It's possible to allow subscribing to a subset of channel patterns} {
         set rd [redis_deferring_client]
         $rd AUTH psuser pspass
@@ -193,6 +227,20 @@ start_server {tags {"acl external:skip"}} {
         $rd close
     } {0}
 
+    test {Subscribers are killed when revoked of channel permission} {
+        set rd [redis_deferring_client]
+        r ACL setuser psuser resetchannels &foo:1
+        $rd AUTH psuser pspass
+        $rd read
+        $rd CLIENT SETNAME deathrow
+        $rd read
+        $rd SSUBSCRIBE foo:1
+        $rd read
+        r ACL setuser psuser resetchannels
+        assert_no_match {*deathrow*} [r CLIENT LIST]
+        $rd close
+    } {0}
+
     test {Subscribers are killed when revoked of pattern permission} {
         set rd [redis_deferring_client]
         r ACL setuser psuser resetchannels &bar:*
@@ -209,16 +257,18 @@ start_server {tags {"acl external:skip"}} {
 
     test {Subscribers are pardoned if literal permissions are retained and/or gaining allchannels} {
         set rd [redis_deferring_client]
-        r ACL setuser psuser resetchannels &foo:1 &bar:*
+        r ACL setuser psuser resetchannels &foo:1 &bar:* &orders
         $rd AUTH psuser pspass
         $rd read
         $rd CLIENT SETNAME pardoned
         $rd read
         $rd SUBSCRIBE foo:1
         $rd read
+        $rd SSUBSCRIBE orders
+        $rd read
         $rd PSUBSCRIBE bar:*
         $rd read
-        r ACL setuser psuser resetchannels &foo:1 &bar:* &baz:qaz &zoo:*
+        r ACL setuser psuser resetchannels &foo:1 &bar:* &orders &baz:qaz &zoo:*
         assert_match {*pardoned*} [r CLIENT LIST]
         r ACL setuser psuser allchannels
         assert_match {*pardoned*} [r CLIENT LIST]
diff --git a/tests/unit/pubsubshard.tcl b/tests/unit/pubsubshard.tcl
new file mode 100644
index 000000000..5c3564afe
--- /dev/null
+++ b/tests/unit/pubsubshard.tcl
@@ -0,0 +1,213 @@
+start_server {tags {"pubsubshard external:skip"}} {
+    proc __consume_ssubscribe_messages {client type channels} {
+        set numsub -1
+        set counts {}
+
+        for {set i [llength $channels]} {$i > 0} {incr i -1} {
+            set msg [$client read]
+            assert_equal $type [lindex $msg 0]
+
+            # when receiving subscribe messages the channels names
+            # are ordered. when receiving unsubscribe messages
+            # they are unordered
+            set idx [lsearch -exact $channels [lindex $msg 1]]
+            if {[string match "sunsubscribe" $type]} {
+                assert {$idx >= 0}
+            } else {
+                assert {$idx == 0}
+            }
+            set channels [lreplace $channels $idx $idx]
+
+            # aggregate the subscription count to return to the caller
+            lappend counts [lindex $msg 2]
+        }
+
+        # we should have received messages for channels
+        assert {[llength $channels] == 0}
+        return $counts
+    }
+
+    proc __consume_subscribe_messages {client type channels} {
+        set numsub -1
+        set counts {}
+
+        for {set i [llength $channels]} {$i > 0} {incr i -1} {
+            set msg [$client read]
+            assert_equal $type [lindex $msg 0]
+
+            # when receiving subscribe messages the channels names
+            # are ordered. when receiving unsubscribe messages
+            # they are unordered
+            set idx [lsearch -exact $channels [lindex $msg 1]]
+            if {[string match "unsubscribe" $type]} {
+                assert {$idx >= 0}
+            } else {
+                assert {$idx == 0}
+            }
+            set channels [lreplace $channels $idx $idx]
+
+            # aggregate the subscription count to return to the caller
+            lappend counts [lindex $msg 2]
+        }
+
+        # we should have received messages for channels
+        assert {[llength $channels] == 0}
+        return $counts
+    }
+
+    proc ssubscribe {client channels} {
+        $client ssubscribe {*}$channels
+        __consume_ssubscribe_messages $client ssubscribe $channels
+    }
+
+    proc subscribe {client channels} {
+        $client subscribe {*}$channels
+        __consume_subscribe_messages $client subscribe $channels
+    }
+
+    proc sunsubscribe {client {channels {}}} {
+        $client sunsubscribe {*}$channels
+        __consume_subscribe_messages $client sunsubscribe $channels
+    }
+
+    proc unsubscribe {client {channels {}}} {
+        $client unsubscribe {*}$channels
+        __consume_subscribe_messages $client unsubscribe $channels
+    }
+
+    test "SPUBLISH/SSUBSCRIBE basics" {
+        set rd1 [redis_deferring_client]
+
+        # subscribe to two channels
+        assert_equal {1} [ssubscribe $rd1 {chan1}]
+        assert_equal {2} [ssubscribe $rd1 {chan2}]
+        assert_equal 1 [r SPUBLISH chan1 hello]
+        assert_equal 1 [r SPUBLISH chan2 world]
+        assert_equal {message chan1 hello} [$rd1 read]
+        assert_equal {message chan2 world} [$rd1 read]
+
+        # unsubscribe from one of the channels
+        sunsubscribe $rd1 {chan1}
+        assert_equal 0 [r SPUBLISH chan1 hello]
+        assert_equal 1 [r SPUBLISH chan2 world]
+        assert_equal {message chan2 world} [$rd1 read]
+
+        # unsubscribe from the remaining channel
+        sunsubscribe $rd1 {chan2}
+        assert_equal 0 [r SPUBLISH chan1 hello]
+        assert_equal 0 [r SPUBLISH chan2 world]
+
+        # clean up clients
+        $rd1 close
+    }
+
+    test "SPUBLISH/SSUBSCRIBE with two clients" {
+        set rd1 [redis_deferring_client]
+        set rd2 [redis_deferring_client]
+
+        assert_equal {1} [ssubscribe $rd1 {chan1}]
+        assert_equal {1} [ssubscribe $rd2 {chan1}]
+        assert_equal 2 [r SPUBLISH chan1 hello]
+        assert_equal {message chan1 hello} [$rd1 read]
+        assert_equal {message chan1 hello} [$rd2 read]
+
+        # clean up clients
+        $rd1 close
+        $rd2 close
+    }
+
+    test "PUBLISH/SUBSCRIBE after UNSUBSCRIBE without arguments" {
+        set rd1 [redis_deferring_client]
+        assert_equal {1} [ssubscribe $rd1 {chan1}]
+        assert_equal {2} [ssubscribe $rd1 {chan2}]
+        assert_equal {3} [ssubscribe $rd1 {chan3}]
+        sunsubscribe $rd1
+        assert_equal 0 [r SPUBLISH chan1 hello]
+        assert_equal 0 [r SPUBLISH chan2 hello]
+        assert_equal 0 [r SPUBLISH chan3 hello]
+
+        # clean up clients
+        $rd1 close
+    }
+
+    test "SUBSCRIBE to one channel more than once" {
+        set rd1 [redis_deferring_client]
+        assert_equal {1 1 1} [ssubscribe $rd1 {chan1 chan1 chan1}]
+        assert_equal 1 [r SPUBLISH chan1 hello]
+        assert_equal {message chan1 hello} [$rd1 read]
+
+        # clean up clients
+        $rd1 close
+    }
+
+    test "UNSUBSCRIBE from non-subscribed channels" {
+        set rd1 [redis_deferring_client]
+        assert_equal {0} [sunsubscribe $rd1 {foo}]
+        assert_equal {0} [sunsubscribe $rd1 {bar}]
+        assert_equal {0} [sunsubscribe $rd1 {quux}]
+
+        # clean up clients
+        $rd1 close
+    }
+
+    test "PUBSUB command basics" {
+        r pubsub shardnumsub abc def
+    } {abc 0 def 0}
+
+    test "SPUBLISH/SSUBSCRIBE with two clients" {
+        set rd1 [redis_deferring_client]
+        set rd2 [redis_deferring_client]
+
+        assert_equal {1} [ssubscribe $rd1 {chan1}]
+        assert_equal {1} [ssubscribe $rd2 {chan1}]
+        assert_equal 2 [r SPUBLISH chan1 hello]
+        assert_equal "chan1 2" [r pubsub shardnumsub chan1]
+        assert_equal "chan1" [r pubsub shardchannels]
+
+        # clean up clients
+        $rd1 close
+        $rd2 close
+    }
+
+    test "SPUBLISH/SSUBSCRIBE with PUBLISH/SUBSCRIBE" {
+        set rd1 [redis_deferring_client]
+        set rd2 [redis_deferring_client]
+
+        assert_equal {1} [ssubscribe $rd1 {chan1}]
+        assert_equal {1} [subscribe $rd2 {chan1}]
+        assert_equal 1 [r SPUBLISH chan1 hello]
+        assert_equal 1 [r publish chan1 hello]
+        assert_equal "chan1 1" [r pubsub shardnumsub chan1]
+        assert_equal "chan1 1" [r pubsub numsub chan1]
+        assert_equal "chan1" [r pubsub shardchannels]
+        assert_equal "chan1" [r pubsub channels]
+    }
+}
+
+start_server {tags {"pubsubshard external:skip"}} {
+start_server {tags {"pubsubshard external:skip"}} {
+    set node_0 [srv 0 client]
+    set node_0_host [srv 0 host]
+    set node_0_port [srv 0 port]
+
+    set node_1 [srv -1 client]
+    set node_1_host [srv -1 host]
+    set node_1_port [srv -1 port]
+
+    test {setup replication for following tests} {
+        $node_1 replicaof $node_0_host $node_0_port
+        wait_for_sync $node_1
+    }
+
+    test {publish message to master and receive on replica} {
+        set rd0 [redis_deferring_client node_0_host node_0_port]
+        set rd1 [redis_deferring_client node_1_host node_1_port]
+
+        assert_equal {1} [ssubscribe $rd1 {chan1}]
+        $rd0 SPUBLISH chan1 hello
+        assert_equal {message chan1 hello} [$rd1 read]
+        $rd0 SPUBLISH chan1 world
+        assert_equal {message chan1 world} [$rd1 read]
+    }
+}
+}
\ No newline at end of file