* optimiz vacuuming volume
* fix bugx
* rename parameters
* fix conflict
* change copyDataBasedOnIndexFile to an instance method
* close needlemap
* optimiz commiting Vacuum volume for leveldb index
* fix bugs
* fix leveldb loading bugs
* refactor
* fix leveldb loading bug
* add leveldb recovery
* add test case for levelDB
* modify test case to cover all the new branches
* use one tmpNm instead of two instances
* refactor
* refactor
* move setWatermark to the end
* add test for watermark and updating leveldb
* fix error logic
* refactor, add test
* check nil before close needlemapeer
add test case
fix metric bug
* add tests, fix bugs
* adjust log level
remove wrong test case
refactor
* avoid duplicate updating metric for leveldb index
