When the receiver starts then the sender gets (by default) 250 credits. As long as the receiver is there the credits keep getting replenished.
When the receiver exits then the router stops giving the sender new credits. The sender still can send the 250 messages to use up the current credits. If you wait long enough then the sender will eventually hang. The messages that are sent to the router when there is no receiver receive 'released' disposition indicating that no receiver on the router got the message. -Chuck ----- Original Message ----- > From: "Vadim Petrenko" <vadim.petre...@ns.nl> > To: users@qpid.apache.org > Sent: Wednesday, October 14, 2020 10:54:53 AM > Subject: RE: Non-blocking Sender with no Receivers > > Hi Ken, > > Yes, we're pre-settling messages already: > connectionfactory.myFactoryLookupSender = > amqp://localhost:5674?jms.presettlePolicy.presettleProducers=true > (dockerized Qpid with an exposed port). > > Making the sending client first check for available credits is a possibility, > but not the ideal option we'd like to use. These clients are not in our > control, it's other teams that develop their applications using our Qpid > network. So we can't really enforce them. Only advise. > > I also noticed some strange behavior which I don't understand. Maybe you guys > can explain. > I've taken the Sender and Receiver from qpid-jms-examples, connected them to > our router network and observed how this works. > 1. When I start the Sender, it gets blocked because there is no receiver (in > the logs I see "Holding Message send until credit is available"). This is as > expected. > 2. I start the Receiver, messages begin to flow, all good. > 3. I kill the Receiver process, but the Sender is still sending messages. To > nowhere. It doesn't timeout either. > > I then proceeded debugging AmqpFixedProducer, which works with credits, and > noticed that on step 1 number of credits it gets via > getEndpoint().getCredit() is 0. So it holds the message. > On the next step Receiver gives it 250 credits. After that, even though the > Receiver process is killed, the number of credits is still 250 and doesn't > get decremented. The Sender continues to send. I expect that credits would > be exhausted at some point. > Is this as it should be? > > Thanks. > > > -----Original Message----- > From: Ken Giusti <kgiu...@redhat.com> > Sent: woensdag 14 oktober 2020 15:18 > To: users <users@qpid.apache.org> > Subject: Re: Non-blocking Sender with no Receivers > > On Wed, Oct 14, 2020 at 8:25 AM Petrenko, Vadim <vadim.petre...@ns.nl> > wrote: > > > Good day, > > > > We’re trying to implement our Qpid dispatch router network in such a > > way that a sender can connect to it at any moment and start sending > > messages to a topic. > > There might be no receivers at this moment, so the messages would be > > just lost. This is ok. > > Then an any moment a receiver(s) can connect and start receiving > > messages currently being sent, then drop off. The sender will just > > continue sending messages, probably into the void. > > > > It’s about sending data from sensors. Sensor data is short living and > > there is no need to buffer it or persist. If no one consumes this data > > in realtime, it can be lost. > > Senders and receivers in our situation are quite volatile, they appear > > and drop off. > > > > As per docs of Qpid: > > === > > Dispatch Router uses a credit-based flow control mechanism to ensure > > that producers can only send messages to a router if at least one > > consumer is available to receive them. Because Dispatch Router does > > not store messages, this credit-based flow control prevents producers > > from sending messages when there are no consumers present. > > === > > > > I was wondering, maybe there is still a workaround or a trick to > > implement the router network the way I described in the beginning? > > If possible without extra brokers and only with Qpid dispatch routers? > > > > Thanks. > > > > > Can your sending client first check whether or not there is credit on the > link and if there is no credit simply drop the message rather than sending > it? > Getting the value of available credit depends on the client API you are > using. For example in Proton-C your sender would call > pn_link_credit(sending_link_ptr) to get the credit for the sending link. > > Also keep in mind that since the application is OK with messages being > dropped you'll want the sender to settle the message after it is sent > (a.k.a. "pre-settled). > > > > > > > ________________________________ > > > > Deze e-mail, inclusief eventuele bijlagen, is uitsluitend bestemd voor > > (gebruik door) de geadresseerde. De e-mail kan persoonlijke of > > vertrouwelijke informatie bevatten. Openbaarmaking, vermenigvuldiging, > > verspreiding en/of verstrekking van (de inhoud van) deze e-mail (en > > eventuele bijlagen) aan derden is uitdrukkelijk niet toegestaan. > > Indien u niet de bedoelde geadresseerde bent, wordt u vriendelijk > > verzocht degene die de e-mail verzond hiervan direct op de hoogte te > > brengen en de e-mail (en eventuele bijlagen) te vernietigen. > > > > Informatie vennootschap<http://www.ns.nl/emaildisclaimer> > > > > > -- > -K > > ________________________________ > > Deze e-mail, inclusief eventuele bijlagen, is uitsluitend bestemd voor > (gebruik door) de geadresseerde. De e-mail kan persoonlijke of > vertrouwelijke informatie bevatten. Openbaarmaking, vermenigvuldiging, > verspreiding en/of verstrekking van (de inhoud van) deze e-mail (en > eventuele bijlagen) aan derden is uitdrukkelijk niet toegestaan. Indien u > niet de bedoelde geadresseerde bent, wordt u vriendelijk verzocht degene die > de e-mail verzond hiervan direct op de hoogte te brengen en de e-mail (en > eventuele bijlagen) te vernietigen. > > Informatie vennootschap<http://www.ns.nl/emaildisclaimer> > > --------------------------------------------------------------------- > To unsubscribe, e-mail: users-unsubscr...@qpid.apache.org > For additional commands, e-mail: users-h...@qpid.apache.org > > --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@qpid.apache.org For additional commands, e-mail: users-h...@qpid.apache.org
