Summary:
Extend the periodic statistics in the info log with the total amount of garbage
in blob files and the space amplification pertaining to blob files, where the
latter is defined as `total_blob_file_size / (total_blob_file_size - total_blob_garbage_size)`.
Also expose the space amp via the `rocksdb.blob-stats` DB property.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9538
Test Plan: `make check`
Reviewed By: riversand963
Differential Revision: D34126855
Pulled By: ltamasi
fbshipit-source-id: 3153e7a0fe0eca440322db273f4deaabaccc51b2
073ac54739