Zhongyi Xie c4f5d0aa15 add GetStatsHistory to retrieve stats snapshots (#4748) ... Summary: This PR adds public `GetStatsHistory` API to retrieve stats history in the form of an std map. The key of the map is the timestamp in microseconds when the stats snapshot is taken, the value is another std map from stats name to stats value (stored in std string). Two DBOptions are introduced: `stats_persist_period_sec` (default 10 minutes) controls the intervals between two snapshots are taken; `max_stats_history_count` (default 10) controls the max number of history snapshots to keep in memory. RocksDB will stop collecting stats snapshots if `stats_persist_period_sec` is set to 0. (This PR is the in-memory part of https://github.com/facebook/rocksdb/pull/4535) Pull Request resolved: https://github.com/facebook/rocksdb/pull/4748 Differential Revision: D13961471 Pulled By: miasantreble fbshipit-source-id: ac836d401ecb84ea92216bf9966f969dedf4ad04		2019-02-20 15:52:54 -08:00
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rocksdb	add GetStatsHistory to retrieve stats snapshots (#4748)	2019-02-20 15:52:54 -08:00