ISSUE-2083: checkpoint when entry has one more directory to write

[sijie]

Original Issue: apache#2083

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QUESTION
when there are one more entry dir to write, entry log will divide into several part in different directory，when one entry log file is full，it will checkpoint，but between the last checkpoint and the current checkpoint， not all data are put in the full entry log， some maybe in another entry log，because there are one more directory，if checkpoint success, some data may not persist in another entry log.