I have implemented MongoDB Change Stream in a Java Microservice, When i do a replica of my Microservice I See change stream watch is listening twice. Code is duplicated. Any way to stop this?
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Run the application one time? – D. SM Aug 13 '20 at 17:49
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check this link : https://stackoverflow.com/questions/52007693/mongo-change-streams-running-multiple-times-kind-of-node-app-running-multiple – Nitish Singla Aug 16 '20 at 05:13
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I gave a similar answer here, however as this question is directly related to Java, I feel it is actually more relevant on this question. I assume what you are after is each change being processed only once among many replicated processes.
Doing this with strong guarantees is difficult but not impossible. I wrote about the details of one solution here: https://www.alechenninger.com/2020/05/building-kafka-like-message-queue-with.html
This solution is implemented in a proof-of-concept library written in Java that accomplishes this which you are free to use/fork (the blog post explains how it works).
It comes down to a few techniques:
- Each process attempts to obtain a lock
- Each lock (or each change) has an associated fencing token
- Processing each change must be idempotent
- While processing the change, the token is used to ensure ordered, effectively-once updates.
More details in the blog post.
Alec Henninger
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