Summary:
On initial call to BlobDBImpl::WaStats() `all_periods_write_` would be empty, so it will crash when we call pop_front() at line 1627. Apparently it is mean to pop only when `all_periods_write_.size() > kWriteAmplificationStatsPeriods`.
The whole write amp calculation doesn't seems to be correct and it is not being exposed. Will work on it later.
Test Plan
Change kWriteAmplificationStatsPeriodMillisecs to 1000 (1 second) and run db_bench --use_blob_db for 5 minutes.
Closes https://github.com/facebook/rocksdb/pull/2751
Differential Revision: D5648269
Pulled By: yiwu-arbug
fbshipit-source-id: b843d9a09bb5f9e1b713d101ec7b87e54b5115a4
29877ec7b4