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  1. Communication protocol is peer-to-peer protocol: every message is sent between one node-sender and one node-receiver.
  2. Communication protocol is an internal protocol used for system messages exchange between Ignite nodes:
    1. There is a limited amount of peers, and all peers are aware of versions of each other.
    2. All peers are aware of all possible messages and their schemas.
    3. At most time peers are of same version. In short period of time (during RU) messags schemas might differ, but not much (few messages might differ with few fields only).
  3. It is proposed to provide compatibility between versions that differ by 1 minor version, for example between 2.20.X and 2.19.X (but not between 2.20.X and 2.18.X).
  4. Messages can be pretty big, contains cache entries (putAll, historic rebalance).
  5. Code changes should be minimal.
  6. Users applications deployed on cluster (services, etc) must support compatibility by itself.

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  1. Message#writeTo, Message#readFrom logic is depends on a remote IgniteProductVersion.
  2. Message#writeTo, Message#readFrom is auto-generated and stored separately from Message DTO classes.Add Message#marshal(Marshaller), Message#unmarshal(Marshaller) methods - to marshal POJO fields if needed. 
  3. Message fields contain:
    1. primitive classes
    2. known collections
    3. POJO - that are other Message
    4. Users classes and java functions (e.g. ComputeJob), that will be serialized with JdkMarshaller
    5. byte[] fields (objects serialized externally) must be avoided as much as possible, because their compatibility can't be guaranteed
  4. Add @Since, @Until  annotations for Message classes and fields.

JavaSerialization 

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  1. byte[] fields in Message must be forbidden.

Marshaller 

  1. Marshaller#marshal, Marshaller#unmarshal is depends on remote IgniteProductVersion.Code generator must inject JdkMarshaller into Message and use it during serialization if JavaSerialization annotation is used. 

Version check

  1. Ignite CI must notify for IF-clauses with condition based on IgniteVersion older than (curVer - 1).
  2. Ignite CI must forbid code changes if Message DTO changed without corresponding @Since, @Until annotations.
  3. Ignite CI must forbid code changes if Message DTO contains byte[] fields.

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