lhotari commented on PR #24625:
URL: https://github.com/apache/pulsar/pull/24625#issuecomment-3232734535

   > @lhotari @coderzc @chrisqwang3 Why do we already have max-delivery-delay, 
and we still need a fixed-delivery-delay? I understand that this PIP is to fix 
the delay time of the message, but it feels strange when I see that 
fixed-delivery-delay can overwrite max-delivery-delay.
   
   There is a reason. When all messages in a topic have the same delay, there 
will be significantly less state to manage. A system can be designed in a way 
where topics are used as schedulers and this will also work at very high scale 
without issues. This would work well with InMemoryDelayedDeliveryTracker since 
it has the `delayedDeliveryFixedDelayDetectionLookahead` feature (#16609, 
#17907). There's no need to build a large index of the delayed messages.
   
   
https://github.com/apache/pulsar/blob/84205ebd849479edac2c6533ea9259091e2e5bed/conf/broker.conf#L659-L663
   
   > Why don‘t we continue to use max-delivery-delay, and then add a 
configuration similar to delivery-delay-type? It can be FIXED or VARIABLE. If 
it is FIXED, it is a fixed delay time.
   
   Here's the current DelayedDeliveryPolicies class:
   
https://github.com/apache/pulsar/blob/master/pulsar-client-admin-api/src/main/java/org/apache/pulsar/common/policies/data/DelayedDeliveryPolicies.java#L23-L41
   
   I guess the reason is that we would break backwards compatibility if we'd 
make changes in the way that you are suggesting.
   
   


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