We want to measure the time it takes for checkpoint cleanup to cleanup files. This will make it possible to track its activity across the fleet.

The time we measure will be different depending the WT version:

• Since 8.0, checkpoint cleanup has its own thread so we will measure the time it takes for the thread to process all the files in its queue.
• Before 8.0, checkpoint cleanup is just another stage of checkpoint. Therefore, we will aggregate the time checkpoint cleanup takes for each collection and report it once checkpoint is done.