Zhengzhi Xu reports:
The compaction threshold mechanism is misleading in current document.
CompactionThreshold is percentage of remaining live data in the oplog at which an oplog is compactable, while current user document is described as percentage of garbage in the oplog like the below:
--compaction-threshold: Percentage of garbage allowed in the file before it is eligible for compaction.
The correct description is in the API document:
DiskStoreFactory setCompactionThreshold(int compactionThreshold) Sets the threshold at which an oplog will become compactable. Until it reaches this threshold the oplog will not be compacted. The threshold is a percentage in the range 0..100. When the amount of live data in an oplog becomes less than this percentage then when a compaction is done this garbage will be cleaned up freeing up disk space. Garbage is created by entry destroys, entry updates, and region destroys. Parameters: compactionThreshold - percentage of remaining live data in the oplog at which an oplog is compactable