Feifan Wang created FLINK-32130:
-----------------------------------

             Summary: previous checkpoint will be broke by the subsequent 
incremental checkpoint
                 Key: FLINK-32130
                 URL: https://issues.apache.org/jira/browse/FLINK-32130
             Project: Flink
          Issue Type: Bug
            Reporter: Feifan Wang


Currently, _SharedStateRegistryImpl_ will discard old one while register new 
state to same key:
{code:java}
// Old entry is not in a confirmed checkpoint yet, and the new one differs.
// This might result from (omitted KG range here for simplicity):
// 1. Flink recovers from a failure using a checkpoint 1
// 2. State Backend is initialized to UID xyz and a set of SST: { 01.sst }
// 3. JM triggers checkpoint 2
// 4. TM sends handle: "xyz-002.sst"; JM registers it under "xyz-002.sst"
// 5. TM crashes; everything is repeated from (2)
// 6. TM recovers from CP 1 again: backend UID "xyz", SST { 01.sst }
// 7. JM triggers checkpoint 3
// 8. TM sends NEW state "xyz-002.sst"
// 9. JM discards it as duplicate
// 10. checkpoint completes, but a wrong SST file is used
// So we use a new entry and discard the old one:
LOG.info(
        "Duplicated registration under key {} of a new state: {}. "
                + "This might happen during the task failover if state backend 
creates different states with the same key before and after the failure. "
                + "Discarding the OLD state and keeping the NEW one which is 
included into a completed checkpoint",
        registrationKey,
        newHandle);
scheduledStateDeletion = entry.stateHandle;
entry.stateHandle = newHandle; {code}
But if _execution.checkpointing.max-concurrent-checkpoints_ > 1, the following 
case will fail (take _RocksDBStateBackend_ as an example):
 # cp1 trigger: 1.sst be uploaded to file-1, and register <1.sst,file-1>, cp1 
reference file-1
 # cp1 is not yet complete, cp2 trigger: 1.sst be uploaded to file-2, and try 
register <1.sst,file-2>. SharedStateRegistry discard file-1
 # cp1 completed and cp2 failed, but the cp1 is broken (file-1 has be deleted)

I think we should allow register multi state object to same key, WDYT 
[~pnowojski], [~roman]  ?



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