Haobo Xu 9e0e6aa7f6 [RocksDB] make sure KSVObsolete does not get accessed as a valid pointer.
Summary: KSVObsolete is no longer nullptr and needs to be checked explicitly. Also did some minor code cleanup and added a stat counter to track superversion cleanups incurred in the foreground.

Test Plan: make check

Reviewers: ljin

Reviewed By: ljin

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16701
2014-03-10 12:55:25 -07:00
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2014-03-10 12:09:54 -07:00