Details
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Bug
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Status: Closed
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Major
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Resolution: Invalid
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None
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None
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Description
Whenever taking snapshots of RocksDBKeyedStateBackend, the values in the states will be written onto different files according to their key groups. The procedure is very costly when the states are very big.
Given that the snapshot operations will be performed much more frequently than restoring, we can leave the key groups as they are to improve the overall performance. In other words, we can perform the grouping of keys in restoring instead of in checkpointing.
I think, the implementation will be very similar to the restoring of non-partitioned states. Each task will receive a collection of snapshots each of which contains a set of key groups. Each task will restore its states from the given snapshots by picking values in assigned key groups.