Summary:
In level compaction, if the total size (even if compensated after taking account of the deletions) of a level hasn't exceeded the limit, but there are lots of deletion entries in some SST files of the level, these files should also be good candidates for compaction. Otherwise, queries for the deleted keys might be slow because they need to go over all the tombstones.
This PR adds an option `deletion_ratio` to the factory of `CompactOnDeletionCollector` to configure it to trigger compaction when the ratio of tombstones >= `deletion_ratio`.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6806
Test Plan:
Added new unit test in `compact_on_deletion_collector_test.cc`.
make compact_on_deletion_collector_test && ./compact_on_deletion_collector_test
Reviewed By: ajkr
Differential Revision: D21511981
Pulled By: cheng-chang
fbshipit-source-id: 65a9d0150e8c9c00337787686475252e4535a3e1
b9d65f5aa6