​More compactions meaning "actual number of compaction tasks". A compaction
task generally operates on many SSTables (how many depends on the chosen
compaction strategy). The number of pending tasks does not line up with the
number of SSTables that will be compacted. 1 task may compact many SSTables.
If your pending tasks are jumping "into the thousands" you're quite
possibly flushing data from memtables faster than you can compact them.
Ideally your pending compactions shouldn't really go above 10 (or 5 even),
and if they are you're possibly overloading the cluster.
