The list of commits that we would like to backport:
- Speed up COLLSCAN for oplog
- Schedule compactions to clean up tombstones
- Don't let iterations spill to the next prefix
- Compact oplog every 30 minutes
- Fix calculation of _maxPrefix
- Speed up RocksIndexBase::getSpaceUsedBytes and RocksEngine::getIdentSize
- Enable block cache size to be changed during runtime
- Optimize insertions into capped collections
- For each prefix, add a key <prefix> to RocksDB
- Add support for displaying thread status
- Change the default compaction to dynamic leveled
- Fix background index build concurrency