Ivan Andika created HDDS-15729:
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Summary: Improve the PlacementPolicy code structure
Key: HDDS-15729
URL: https://issues.apache.org/jira/browse/HDDS-15729
Project: Apache Ozone
Issue Type: Improvement
Reporter: Ivan Andika
Assignee: Ivan Andika
The PlacementPolicy (both Pipeline Placement Policy and the Container Placement
Policy) is poorly abstracted which is very hard to reason about. There are a
lot of leaky abstractions or logic specific to a replication config (e.g. Ratis
logic in interface that can also be applied to EC). I found myself getting lost
every time I look at the placement policy logic since it's hard to build a
mental model of the whole process. This task is to identify them and fix them
for better readability and maintainability, as well as document the exact
contracts and responsibilities of these policies.
For example (not exhaustive)
* PlacementPolicy is supposed to be generic, but we have container placement
specific logic like validateContainerPlacement and
replicasToCopyToFixMisReplication and replicasToRemoveToFixOverreplication
* PipelinePlacementPolicy seems to only used for RATIS pipeline, but we have
EC pipeline, so it gives an impression that PipelinePlacementPolicy can also be
used for EC, which AFAIK is not the case.
** PipelinePlacementPolicy is only used for RATIS, then we should make it
explicit by changing the name to RatisPipelinePlacementPolicy
** PipelinePlacementPolicy also have internal "Ratis" related pipelines like
* We are still using PlacementPolicy for everything, even if
PipelinePlacementPolicy is more appropriate for pipeline related matters, which
forces PlacementPolicy to implement interfaces that it should not be
implementing
** For example, in RatisPipelineProvider we can change PlacementPolicy to
PipelinePlacementPolicy since we are dealing with pipeline
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