"Function to calculate maximum purgeable timestamp is made 10 times faster when
compacting sstables overlap with 10% of all sstables.
That's possible with an incremental selector that will incrementally select
sstables based on key being compacted.
Currently, we iterate through all non-compacting sstables and consult their
bloom filter to determine max purgeable timestamp, and that will be very
expensive for compactions that are frequently deciding whether or not to purge
tombstones."
* 'filter_overhead_fix_v4' of github.com:raphaelsc/scylla:
compaction: reduce bloom filter overhead with incremental selector
tests: add test for sstable set's incremental selector
sstable_set: introduce incremental selector
compatible_ring_position: add function to return token
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