This part of pruning can be very expensive and bog down the whole
instance to an unusable sate for a long time. It can thus be desireable
to split it from prune_objects and run it on its own in smaller limited batches.
If the batches are smaller enough and spaced out a bit, it may even be possible
to avoid any downtime. If not, the limit can still help to at least make the
downtime duration somewhat more predictable.
Oneric
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