torwig commented on code in PR #1657:
URL: https://github.com/apache/kvrocks/pull/1657#discussion_r1290163655
##########
src/commands/cmd_pubsub.cc:
##########
@@ -27,20 +27,48 @@ namespace redis {
class CommandPublish : public Commander {
public:
- // mark is_write as false here because slave should be able to execute
publish command
Status Execute(Server *svr, Connection *conn, std::string *output) override {
if (!svr->IsSlave()) {
- // Compromise: can't replicate message to sub-replicas in a
cascading-like structure.
- // Replication relies on WAL seq, increase the seq on slave will break
the replication, hence the compromise
+ // Compromise: can't replicate a message to sub-replicas in a
cascading-like structure.
+ // Replication relies on WAL seq; increasing the seq on a replica will
break the replication process,
+ // hence the compromise solution
redis::PubSub pubsub_db(svr->storage);
+
auto s = pubsub_db.Publish(args_[1], args_[2]);
if (!s.ok()) {
return {Status::RedisExecErr, s.ToString()};
}
}
int receivers = svr->PublishMessage(args_[1], args_[2]);
+
*output = redis::Integer(receivers);
+
+ return Status::OK();
+ }
+};
+
+class CommandMPublish : public Commander {
+ public:
+ Status Execute(Server *svr, Connection *conn, std::string *output) override {
+ int total_receivers = 0;
+
+ for (size_t i = 2; i < args_.size(); i++) {
+ if (!svr->IsSlave()) {
+ redis::PubSub pubsub_db(svr->storage);
+
+ auto s = pubsub_db.Publish(args_[1], args_[i]);
+ if (!s.ok()) {
+ return {Status::RedisExecErr, s.ToString()};
+ }
+ }
+
+ int receivers = svr->PublishMessage(args_[1], args_[i]);
+ total_receivers += receivers;
+ }
+
+ *output = redis::Integer(total_receivers);
Review Comment:
In general, I think it's not easy to utilize the return value of the
`PUBLISH` command, except to check whether it is 0 or more. The actual goal of
Pub/Sub pattern is to decouple publishers from subscribers and if I want to
check the number of receivers I should know the exact number of them. And for
example, if I know that there should be 5 subscribers but I received only 4 in
response to the `PUBLISH` command, what should I do?
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