Summary:
If GC kicks in between
* A Get() reads index entry from base db.
* The Get() read from a blob file
The GC can delete the corresponding blob file, making the key not found. Fortunately we have existing logic to avoid deleting a blob file if it is referenced by a snapshot. So the fix is to explicitly create a snapshot before reading index entry from base db.
Closes https://github.com/facebook/rocksdb/pull/2754
Differential Revision: D5655956
Pulled By: yiwu-arbug
fbshipit-source-id: e4ccbc51331362542e7343175bbcbdea5830f544
5b68b114f1