Issue
I have 3 nodes of my application (Java Spring boot) which use Hazelcast IMap as a distributed cache. My logic requires to frequently update a value in the map, and I have implemented a EntryProcessor for it. Whilst testing, I have created a hazelcast cluster with 3 nodes. What I noticed is following:
- if node1 invokes the entry processor, it is not guaranteed that it will be executed on node 1. It is executed on any one of those 3 nodes. Same for backup entry processor.
- same happens for the other 2 nodes.
Is there any way to ensure/enforce that the entry processor is executed on the node where it was invoked? I read through the documentation and could not find an answer for my question.
Thanks in advance.
Solution
The entry processor runs on nodes that host the primary copy of the entry and any backup copy.
The behaviour you are seeing is due to the data not being hosted in the same place from run to run. There is a degree of randomness.
This is normal, and what you want. Any attempts to "pin" the data to a specific place ALWAYS go wrong. Hazelcast, and distributed stores in general, need to be unconstrained in where they can place the data to balance the cluster.
You can run a Runnable/Callable on a specific node if you need predictability, but that's not the use-case here.
Answered By - Neil Stevenson
Answer Checked By - Robin (JavaFixing Admin)
