I am not following your objections to the protocol solution. It might
be more productive if I provided a draft PR with a sample
implementation. I'm not sure that I'll have time, but I'll try to put
something together this week.
> At least it will simplify the process of using cumulative ack with the
> transaction.
Is this the underlying motivation for the PIP?
>From my perspective, the PIP is seeking to decrease duplicate messages
experienced due to disconnections from the broker.
> The problem of the resetting cursor can be optimized in the future
Why should we push off solving this problem? It seems fundamental to
this PIP and should not be ignored. At the very least, I think we need
to have an idea of what the future solution would be before we defer
its implementation.
Thanks,
Michael
On Tue, Mar 21, 2023 at 10:52 PM 丛搏 <congbobo...@gmail.com> wrote:
>
> Hi, Michael
> > In this case, the consumer does not have the source of truth for the
> > readPosition. It would leave the new protocol field for `readPosition`
> > empty and the broker would use its source of truth for the read
> > position.
> application has received all the messages by application thread. we also need
> a
> correct `startPosition`, right? but in your way, we will think about
> the consumer
> hasn't received any messages.
>
> >
> > > why do we need to invoke `BlockingQueue.take` and `synchronized` in the
> > > same logic? it's a bad code.
> >
> > We don't need to synchronize this code here because the logic will
> > come after the consumer has been disconnected from broker a and before
> > it is connected to broker b.
> The application takes a message from the queue then reconnect,
> the SubCommond can use the right startPostion? example:
> 1. application receives one message with `MessageId = 1`
> 2. consumer reconnect discovers the queue is empty, and the
> lastDequeMessageId doesn't change.
> 3. consumer sends a subcommand with MessageId.earliest, the `MessageId = 1`
> will redeliver from broker to client consumer, right?
>
> As we can see in the example, the application also can receive
> `MessageId = 1`, right?
> > We would not need to lock here because we do not enqueue new messages
> > after we've been disconnected from the broker and before we've sent
> > CommandSubscribe.
> we can see the code [0], the thread has changed.
> Where do we guarantee that no new messages will come in?
>
> >
> > Ultimately, I think a protocol solution will yield better results,
> > especially since we'll want to implement this feature in the other
> > client languages.
> The problem of the resetting cursor can be optimized in the future,
> but can you ensure the
> correctness of all the cases I mentioned above? IMO, if we use my
> design, client change,
> we don't need the broker to make any changes. its simple and it's easy
> to implement.
> I can make sure it's completely correct, I can make sure it's
> completely correct. In your design,
> I currently do not see a closed-loop implementation that can achieve
> at least in the java client.
>
> Thanks,
> Bo
> >
> > Thanks,
> > Michael
> >
> > On Tue, Mar 21, 2023 at 9:29 PM 丛搏 <congbobo...@gmail.com> wrote:
> > >
> > > Hi, Michael:
> > >
> > > Michael Marshall <mmarsh...@apache.org> 于2023年3月21日周二 23:17写道：
> > >
> > > >
> > > > One more point. Instead of keeping track of the latest message seen by
> > > > the application, the logic in my solution would actually just check
> > > > the last message in the `incomingMessages` queue (as in the most
> > > > recently added), and use that as the read position in the subscribe
> > > > command. If we made this change, we would have to change this code [0]
> > > > to not drop the `incomingMessages` queue.
> > >
> > > case 1:
> > > What we define the message that the application has seen?
> > > I think it is the[0], when the `incomingMessages` queue is empty,
> > > how do we get the correct `startPosition`?
> > > What I think we should lock the receive logic in [1]
> > > ```
> > > synchronized (this) {
> > > message = incomingMessages.take();
> > > messageProcessed(message);
> > > }
> > > ```
> > > why do we need to invoke `BlockingQueue.take` and `synchronized` in the
> > > same logic? it's a bad code.
> > >
> > > case 2:
> > > If we sub with `startMessageId`, we also should lock any enqueue
> > > logic, like [2] and
> > > check to consumer's current state
> > > ```
> > > synchronized (this) {
> > > if (consumer.isConnected) {
> > > if (canEnqueueMessage(message) &&
> > > incomingMessages.offer(message)) {
> > > // After we have enqueued the messages on
> > > `incomingMessages` queue, we cannot touch the message
> > > // instance anymore, since for pooled messages, this
> > > instance was possibly already been released
> > > // and recycled.
> > > INCOMING_MESSAGES_SIZE_UPDATER.addAndGet(this, messageSize);
> > > getMemoryLimitController().ifPresent(limiter ->
> > > limiter.forceReserveMemory(messageSize));
> > > updateAutoScaleReceiverQueueHint();
> > > }
> > > }
> > > }
> > > ```
> > > case 3:
> > > when we subcommand sends to broker with `startMessageId = 1`, then the
> > > broker push message
> > > has not yet entered `incommingQueue`, the application invokes
> > > redeliver. in this way, we don't
> > > filter messages are correct, right?
> > >
> > > These are some cases that I simply thought of, and there must be
> > > others that I haven't thought
> > > of. Are you sure we can handle these problems correctly?
> > >
> > > > The problem of "the consumer doesn't know" seems like something that
> > > > is reasonably within the protocol's responsibilities. In this case, an
> > > > event happens on the broker, and the broker can tell the consumer.
> > >
> > > I don't think a simple change protocol can solve these problems,
> > > We can't promise that every consumer can receive the broker reset
> > > cursor request.
> > > When the consumer reconnects, the broker can't send the reset cursor
> > > request to
> > > the client consumers, right? In this case, the consumer is still unaware,
> > > right?
> > >
> > >
> > > [0]
> > > https://github.com/apache/pulsar/blob/30d2469086fea989ac8baf059df8e69c66a68d89/pulsar-client/src/main/java/org/apache/pulsar/client/impl/ConsumerImpl.java#L135
> > > [1]
> > > https://github.com/apache/pulsar/blob/30d2469086fea989ac8baf059df8e69c66a68d89/pulsar-client/src/main/java/org/apache/pulsar/client/impl/ConsumerImpl.java#L440-L454
> > > [2]
> > > https://github.com/apache/pulsar/blob/30d2469086fea989ac8baf059df8e69c66a68d89/pulsar-client/src/main/java/org/apache/pulsar/client/impl/ConsumerBase.java#L875-L892
> > > >
> > > > Thanks,
> > > > Michael
> > > >
> > > > [0]
> > > > https://github.com/apache/pulsar/blob/af1360fb167c1f9484fda5771df3ea9b21d1440b/pulsar-client/src/main/java/org/apache/pulsar/client/impl/ConsumerImpl.java#L789-L795
> > > >
> > > > On Tue, Mar 21, 2023 at 9:46 AM Michael Marshall <mmarsh...@apache.org>
> > > > wrote:
> > > > >
> > > > > > if we add the new field in CommandSubscribe, we should ensure
> > > > > > the synchronization between consumer reconnection and user
> > > > > > calling receive and redeliverUnack method. it will affect the
> > > > > > performance
> > > > > > of receive. expose synchronization to hot paths it not a good idea.
> > > > >
> > > > > I don't think this is a valid objection. I am pretty sure we already
> > > > > synchronize in the relevant places in the consumer to solve the exact
> > > > > race condition you're concerned about: [0] [1].
> > > > >
> > > > > My proposed operation is to keep track of the latest message id that
> > > > > the application has seen, and then tell the broker that id when
> > > > > sending the Subscribe command. We already do similar logic here [2]
> > > > > [3], but instead of getting the first message id the consumer hasn't
> > > > > seen, we'll get the latest message id seen.
> > > > >
> > > > > Regarding performance, the PIP doesn't touch on how it will filter out
> > > > > messages. What is the planned approach? In my understanding, the
> > > > > client will keep track of the latest message id that the application
> > > > > has seen and then will need to compare that message id against every
> > > > > new mess. As such, it seems like telling the broker where to start
> > > > > instead of naively checking a filter on every message would be
> > > > > cheaper.
> > > > >
> > > > > > As described in Compatibility in PIP. Client consumer doesn't know
> > > > > > Pulsar Admin reset cursor.
> > > > >
> > > > > The problem of "the consumer doesn't know" seems like something that
> > > > > is reasonably within the protocol's responsibilities. In this case, an
> > > > > event happens on the broker, and the broker can tell the consumer.
> > > > >
> > > > > > * <p>Consumers should close when the server resets the cursor,
> > > > > > * when the cursor reset success, and then restart. Otherwise,
> > > > > > * the consumer will not receive the history messages.
> > > > >
> > > > > This is introducing a confusing edge case that requires reading a
> > > > > Javadoc in order to understand. That seems risky to me, and I do not
> > > > > think we should add such an edge case. A new protocol message would
> > > > > easily handle it and make it transparent to the application.
> > > > >
> > > > > Thanks,
> > > > > Michael
> > > > >
> > > > > [0]
> > > > > https://github.com/apache/pulsar/blob/af1360fb167c1f9484fda5771df3ea9b21d1440b/pulsar-client/src/main/java/org/apache/pulsar/client/impl/ConsumerImpl.java#L826-L912
> > > > > [1]
> > > > > https://github.com/apache/pulsar/blob/af1360fb167c1f9484fda5771df3ea9b21d1440b/pulsar-client/src/main/java/org/apache/pulsar/client/impl/ConsumerImpl.java#L1870-L1876
> > > > > [2]
> > > > > https://github.com/apache/pulsar/blob/af1360fb167c1f9484fda5771df3ea9b21d1440b/pulsar-client/src/main/java/org/apache/pulsar/client/impl/ConsumerImpl.java#L789-L795
> > > > > [3]
> > > > > https://github.com/apache/pulsar/blob/af1360fb167c1f9484fda5771df3ea9b21d1440b/pulsar-client/src/main/java/org/apache/pulsar/client/impl/ConsumerImpl.java#L922-L960
> > > > >
> > > > > On Tue, Mar 21, 2023 at 8:58 AM Yubiao Feng
> > > > > <yubiao.f...@streamnative.io.invalid> wrote:
> > > > > >
> > > > > > +1
> > > > > >
> > > > > > Hi, Bo :
> > > > > >
> > > > > > Thanks for your explanation. That makes sense to me.
> > > > > >
> > > > > > Thanks,
> > > > > > Yubiao Feng
> > > > > >
> > > > > > On Mon, Mar 20, 2023 at 10:21 PM 丛搏 <congbobo...@gmail.com> wrote:
> > > > > >
> > > > > > > Hi, pulsar community:
> > > > > > >
> > > > > > > I started a PIP about `Client consumer filter received messages`.
> > > > > > >
> > > > > > > PIP: https://github.com/apache/pulsar/issues/19864
> > > > > > >
> > > > > > > Thanks,
> > > > > > > Bo
> > > > > > >
