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• Is there any primitives, building blocks to provide compatibility?
• Difficulties for day by day coding.
  • java serialzation
    • anonymous class names based on declaration order
• Compatibility testing.
  • explicit tests.
  • ability to run tests with random node versions
• New feature implementation, enabling.
• patterns for implementing commons cases: new version of algorithmes, testing against new versions.
• Scope of compatibility: 
  • Currently any third-party module can register own ports (messages?) and must be able to track compatibility. 

Implementation phases

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Code Cleanup

• remove DirectByteBufferStreamImpl  V1-V3, keep V4, only.
• remove all items from IgniteFeatures  and corresponding checks.
• remove all code and checks for GridContinuousProcessor#discoProtoVer
• TcpDiscoverySpi#setForceServerMode
• All old version of classes - keep only max from V2, V3, etc. versions. StartRequestV2 that belongs to internal communication.
  Classes releated to thin client, jdbc, odbc interaction must stay.
  • StartRequest must be deleted. Rename StartRequestV2 → StartRequest.
  • CacheMetricsSnapshot must be deleted. Rename CacheMetricsSnapshotV2 → CacheMetricsSnapshot.
• MessageFactory.
• IgniteDataTransferObject

• EXCHANGE_PROTOCOL_2_SINCE and related code

• IgniteProductVersion.fromString - usages

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BinaryMarshaller modularization

• modularize BinaryMarshaller.
• create small jar for ignite thin client
• provide clear API for binary objects inside ignite-code and other modules.

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Communication SPI Compatibility

• Communication MessageWriter and MessageReader are aware of peers version, and then schema of a message.
• Distinguish serdes generation from POJO
• PR checks for Messages  ancestor change with the some warning, labels, etc. that can draw reviewer attention to the possible compatibility issues.

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Discovery SPI Compatibility

• Serdes changes to provide compatibility? (current approach with JDK serialization provides some compatibility (13).
  Is it enough for long-term compatibility support?
• Serdes changes to restrict classes that can be sent over SPI.
• PR checks for Messages  ancestor change with the some warning, labels, etc. that can draw reviewer attention to the possible compatibility issues.

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Management API

• Provide ability to change arg, result classes in compatible way.
  • Possible approach is to reuse communication serdes framework.
  • Other possibility is to migrate on BinaryObject as a arguments and results.
• PR checks for Messages  ancestor change with the some warning, labels, etc. that can draw reviewer attention to the possible compatibility issues.

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IgniteFeatures 

• Write down clear rules to deal with the new features and not compatible enhancements.
• Support, if not, already this rules in IgniteFeatures framework.

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Compatibility Matrix

• A way to declare one version as incompatible with another.
• A component to enforce a rule that only compatible versions can join one cluster.

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Testing

• ducktests to check upgrade procedure.
• unit tests mode that start some nodes of previous version. 

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Development process changes

• Any change in public API MUST be in the form of IEP.
• Any change in public API MUST be voted by two(three?) committers.
• Documentation with clear description of development rules for all subsystems required to be compatible.

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