GitHub user sihuazhou opened a pull request:

    [FLINK-8639][State Backends]Fix always need to seek multiple times when 
iterator RocksDBMapState

    ## What is the purpose of the change
    This PR addressed issue 
[FLINK-8639]( Currently, 
almost every time we want to iterator a RocksDBMapState we need to do seek at 
least 2 times (Seek is a poor performance action for rocksdb cause it can't use 
the bloomfilter). This is because `RocksDBMapIterator` use a `cacheEntries` to 
cache the seek values every time and the `cacheEntries`'s init size is 1.
    ## Brief change log
    - Change CACHE_SIZE_BASE from 1 to 32.
    - Compare in reverse order in function underSameKey().
    ## Verifying this change
    This change is already covered by existing tests.
    ## Does this pull request potentially affect one of the following parts:
      - Dependencies (does it add or upgrade a dependency): (no)
      - The public API, i.e., is any changed class annotated with 
`@Public(Evolving)`: (no)
      - The serializers: (no)
      - The runtime per-record code paths (performance sensitive): (no)
      - Anything that affects deployment or recovery: JobManager (and its 
components), Checkpointing, Yarn/Mesos, ZooKeeper: (no)
      - The S3 file system connector: (no)
    ## Documentation
      - Does this pull request introduce a new feature? (no)

You can merge this pull request into a Git repository by running:

    $ git pull improve_rocksdb_base_mapstate

Alternatively you can review and apply these changes as the patch at:

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #5465
commit 753855ec2957492ba6c2eb272fdc5ffe7c769608
Author: summerleafs <summerleafs@...>
Date:   2018-02-12T14:28:04Z

    2, Compare in reverse order in function underSameKey().

commit e33b807ba151265e0fd86d52701965dc5ffcb7be
Author: summerleafs <summerleafs@...>
Date:   2018-02-12T14:50:28Z

    change CACHE_SIZE_BASE from 1 to 32.



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