Stefan Richter created FLINK-10043:
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Summary: Refactor object construction/inititlization/restore code
Key: FLINK-10043
URL: https://issues.apache.org/jira/browse/FLINK-10043
Project: Flink
Issue Type: Sub-task
Reporter: Stefan Richter
Assignee: Stefan Richter
Currently, the constructor of {{RocksDBKeyedStateBackend}} has the following
shortcomings:
- It does initialization and cleanup of some directories and files. this makes
it harder to unit-test because dependencies are created in the constructor and
not passed in from outside.
- It leaves many important fields uninitialized and more methods e.g.
{{restore}} _have_ to be called before the object is fully constructed. This is
error-prone in many ways and hard to unit-test. I think the origin of this
problem was introducing incremental snapshots, because in this case, we can
only open a RocksDB instance AFTER the restore code was executed and restored
the working directory.
As a solution, I would suggest to have a dedicated builder class that takes the
current constructor parameters and (optional) the state handles to restore.
Then, this class constructs and intializes all dependencies, and dependencies
are only passed to the new {{RocksDBKeyedStateBackend}} constructor that does
no other work besided assigning dependencies to fields.
With this change, I would also extract the different restore strategies for
incremental and full snapshots out of the main class, into their own classes.
They will then be used in the newly introduced builder from the previous step.
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