Bumping this up. Would really like to discuss this in the community. Regards
On Wed, Jun 28, 2023 at 11:49 PM Girish Sharma <scrapmachi...@gmail.com> wrote: > Hi everyone, I am trying to understand the failover subscription logic a > bit more in detail. Specifically, the doc > <https://pulsar.apache.org/docs/3.0.x/concepts-messaging/#failover>mention > this part for partitioned topic: > > > > * If the number of partitions in a partitioned topic is less than the > number of consumers:For example, in the diagram below, this partitioned > topic has 2 partitions and there are 4 consumers.Each partition has 1 > active consumer and 1 stand-by consumer.* > > > - *For p0, consumer A is the master consumer, while consumer B would > be the next consumer in line to receive messages if consumer A is > disconnected.* > - *For p1, consumer C is the master consumer, while consumer D would > be the next consumer in line to receive messages if consumer C is > disconnected*. > > So, as per this, since all four (A,B,C,D) consumers make connection to > both partitions p0 and p1, the consumers array size in > AbstractDispatcherSingleActiveConsumer should be 4. Now based on the > consumer index choosing logic spanning lines 126 - 130 > <https://github.com/apache/pulsar/blob/master/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/AbstractDispatcherSingleActiveConsumer.java#L126-L130> > , the consumer index assigned to p0 should be 0 (i.e. A) and to p1 should > be 1 (i.e. B) . I am assuming here that all 4 consumers have the same > priority.Now consider consumer B getting disconnected. remaining consumer > array == (A,C,D) . In this case, p1 will get a new consumer using logic 1 > % 3 = 1 index i.e. consumer C now. p0's consumer would remain same i.e. 0 > % 3 = 0 i.e. A. > Now next consider that consumer A also goes down. remaining consumer array > == (C,D) In this case, p0 will get a new consumer -> 0%2 = 0 i.e. > consumer C and p1 would now be shifted to 1%2 = 1 Consumer D . Even > though p1's active consumer was untouched, p1 got a consumer shift.So I > have couple of questions - > > - Am I missing something? Is my understanding of logic correct? > - If yes, why does the doc say what it says? And why change p1's > consumer uselessly in above example > > > Regards > -- > Girish Sharma > -- Girish Sharma
