[jira] [Created] (FLINK-4266) Cassandra Statebackend

["Chen Qin (JIRA)" <ji...@apache.org>]

Chen Qin created FLINK-4266:
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             Summary: Cassandra Statebackend
                 Key: FLINK-4266
                 URL: https://issues.apache.org/jira/browse/FLINK-4266
             Project: Flink
          Issue Type: New Feature
          Components: State Backends, Checkpointing
    Affects Versions: 1.0.3, 1.2.0
            Reporter: Chen Qin
            Priority: Minor


Current FileSystem statebackend limits whole state size to disk space. 
For long running task that hold window content for long period of time, it needs to split out states to durable remote storage and replicated across data centers.

We look into implementation from leverage checkpoint timestamp as versioning and do range query to get current state; we also want to reduce "hot states" hitting remote db per every update between adjacent checkpoints by tracking update logs and merge them, do batch updates only when checkpoint; lastly, we are looking for eviction policy that can identify "hot keys" in k/v state and lazy load those "cold keys" from Cassandra.

For now, we don't have good story regarding to data retirement. We might have to keep forever until manually run command and clean per job related state data. Some of features might related to incremental checkpointing feature, we hope to align with effort there also.

Welcome comments, I will try to put a draft design doc after gathering some feedback.









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