pkumar-singh opened a new pull request, #887:
URL: https://github.com/apache/pulsar-client-go/pull/887

   Motivation
   
   When a topic is a partitioned topic and a partition is not available for 
producing messages, currently pulsar client will still try to produce messages 
on unavailable partitions, which it may not necessarily need to do in certain 
cases. Pulsar Client may simply pick up another partition and try producing in 
certain cases.
   Partition Unavailable
   There could be a plethora of reasons a partition can become unavailable. But 
the most prominent reason is partition is moving from one broker to another, 
and until every actor is in sync with which broker owns the partition, the 
partition will be unavailable for producing. Actors are producers, old broker, 
new broker.
   
   Client Behavior
   This is the typical produce code.
   producer.sendAsync(payLoad.getBytes(StandardCharsets.UTF_8));
   
   When send is called message is enqueued in a queue(called pending message 
queue) and the future is returned.
   And future is only completed when the message is picked from the queue and 
sent to the broker asynchronously and ack is received asynchronously again. Max 
size of the pending message queue is controlled by producer config 
maxPendingMessages.
   When pending message queue is full, the application will start getting 
publish failures. Pending message queue provide a cushion towards unavailable 
partitions. But again it has some limits.
   
   When another partitions can be picked
   
   When the message is not keyed. That means the message is not ordered based 
on a key.
   When routing mode is round-robin, that means a message can be produced to 
any of the partitions. So If a partition is unavailable try and pick up another 
partition for producing, by using the same round-robin algorithm.


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