I've submitted a PR for issue IOTDB-606

[戚厚亮]

hi, all



The current MetaSnapshot is using the simplest way, storing the raw committed 
logs. This pr replaceS the logs with some metadata.

I hope this PR is helpful. 




PR: https://github.com/apache/incubator-iotdb/pull/1154

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Thanks,
Houliang Qi
戚厚亮