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由 Dhruba Borthakur 提交于
Summary: LevelDB should delete almost-new keys when a long-open snapshot exists. The previous behavior is to keep all versions that were created after the oldest open snapshot. This can lead to database size bloat for high-update workloads when there are long-open snapshots and long-open snapshot will be used for logical backup. By "almost new" I mean that the key was updated more than once after the oldest snapshot. If there were two snapshots with seq numbers s1 and s2 (s1 < s2), and if we find two instances of the same key k1 that lie entirely within s1 and s2 (i.e. s1 < k1 < s2), then the earlier version of k1 can be safely deleted because that version is not visible in any snapshot. Test Plan: unit test attached make clean check Differential Revision: https://reviews.facebook.net/D6999
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