sijie edited a comment on issue #4062: Delayed message delivery implementation URL: https://github.com/apache/pulsar/pull/4062#issuecomment-484199134 > Is that a bad thing? Is there any limitation in this approach? > The changes to the dispatcher itself have been isolated in a very few specific points. It is not a bad thing. I am actually super happy to see this happen because I am a supporter for broker-side approaches from the beginning (if you have followed the email discussion). If you took a look at [my comment](https://github.com/apache/pulsar/pull/4062#pullrequestreview-227588319), PIP-26 also isolates the changes to a structure called `DelayedMessageIndex` (which is the structure you called DelayedDeliveryTracker here). So technically there are no fundamental differences between this PR and PIP-26 regarding the concerns around changes touching dispatcher. I am just trying to figure out why and make sure the authors of PIP-26 also understand your thoughts behind this. IMO that is an important thing for building a healthy community. > The biggest difference with this PR is that the tracking happens entirely off-heap, in direct memory. There are no objects created and retained for extended amount of time, which is the pattern that will kill the GC performances. I don't think the biggest difference with this PR and PIP-26 is the direct memory thing you mentioned on implementing DelayDeliveryTracker. The delayed message index in PIP-26 can also be implemented using direct memory without allocation. IMO the difference between this PR and PIP-26 is - `DelayedDeliveryTracker` in this PR is a pure memory structure which can not hold "delayed index" beyond memory; `DelayedMessageIndex` in PIP-26 is a time partitioned structure which can spool the index back to ledgers. `DelayedDeliveryTracker` is limited at the delay ranges that it can support. `DelayedMessageIndex` is a more generic approach on supporting arbitrary delays or scheduled messages. `DelayedDeliveryTracker` and `DelayedMessageIndex` are just two different implementations of one same things. If the current implementation of `DelayedDeliveryTracker` is acceptable, why the proposal of a time-partitioned `DelayedMessageIndex` is not acceptable? People can choose which implementation to use by configuring a configuration in the broker configuration. Lastly, PIP-26 already presents changes regarding api, protocol, namespace policies and many other changes around this area. Shall we just pickup the proposed changes there instead of starting a new effort?
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