Summary:
Update DB::AddFile() restrictions to be
- Key range in loaded table file don't overlap with existing keys or tombstones in DB.
- No other writes happen during AddFile call.
The updated AddFile() will verify that the file key range don't overlap with any keys or tombstones in the DB, and then add the file to L0
Test Plan: unit tests
Reviewers: igor, rven, anthony, kradhakrishnan, sdong
Reviewed By: sdong
Subscribers: adsharma, ameyag, dhruba
Differential Revision: https://reviews.facebook.net/D49233
ff4499e297