Wellington Chevreuil created HBASE-28044:
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             Summary: Reduce frequency of saving backing map in persistence 
cache
                 Key: HBASE-28044
                 URL: https://issues.apache.org/jira/browse/HBASE-28044
             Project: HBase
          Issue Type: Sub-task
            Reporter: Wellington Chevreuil
            Assignee: Wellington Chevreuil


Currently we always write the whole cache mapping into the persistent map file. 
This is not a lightweight operation, on a full 1.6TB cache with ten millions of 
block, this can grow as much as 10GB. In the current persistent cache 
implementation, we flush it to disk every 1s. If we raise the "checkpoint" 
period, we risk lose more cache events in the event of a recovery. 

This proposes reduce the frequency needed to save the backing map as follows:
1) Save every block addition/eviction into a single file in disk;
2) Checkpoint at higher intervals, consolidating all transactions into the 
larger map file;
3) In the event of failure, recovery would consist of loading the latest map 
file, then applying all the transactions files sequentially;



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