Hazelcast 3.8 EntryAdded or EntryUpdated eventlisteners are NOT invoked when an entry is loaded from maptsore

Question

I am trying to set TTL on a record in IMap which is loaded from cassandra mapStore. To achieve this I have implemented an EntryAdded and a EntryUpdated eventlistener for the IMap.But the methods aren't invoked when I read the data from mapstore and put it back to hazelcast.

Is my expectation wrong? If so then what are the possible solutions to achieve this?

Thanks

Answer 1

MapLoader.loadAll() will generate he ADDED event when the IMap is initially populated. Thereafter MapLoader.load() won't generate the ADDED event for objects loaded afterwards.

This is inconsistent, and logged as an issue, https://github.com/hazelcast/hazelcast/issues/7771

Even once this is fixed, it won't set the TTL on entry differently from another.

For that, you may want to investigate the "cache-aside" design pattern, where your code tests the IMap for data presence, and does a Cassandra retrieve and Hazelcast save, which would allow a different TTL per entry.

Answer 2

I don't think its possible to set the TTL while loading entry using MapLoader. Below is the approach you can follow: 1. Check if the entry is not in cache 2. If not in the cache - get it from data store. Use PUT method which will allow to set the TTL. You can wrap this logic inside Hazelcast Callable which can configured as partition aware. This will save the network cost as it will execute the code on the node where data resides