"In time-series, it's common for tables in a given time window to be eventually
fully expired. The deletion of such tables is done by compaction, but there's
*no* need to *actually* compact such fully expired sstables *iff* their full
deletion will not cause older data to be ressurected. In other words, a fully
expired table can be actually skipped (but deleted in the end) by compaction
*iff* it doesn't contain newer data than its overlapping counterparts. So there
may be false negatives, but never false positives.
All that said, the goal behind this patchset is to save read bandwidth of disk
in such scenarios. Given that fully expired sstables will not be read by
compaction process anymore, read amplification will be greatly reduced too.
Fixes #2620."
* 'time_series_performance_improvement_v2_2' of github.com:raphaelsc/scylla:
tests: check sstable auto correct bad max deletion time
tests: add test for compaction with fully expired table
sstables/compaction: do not actually compact fully expired sstables
sstables: make sstable auto correct max_local_deletion_time
sstables: switch to const ref wherever possible
sstables: use gc_clock::time_point for gc_before
gc_clock: introduce operator<<(ostream&, gc_clock::time_point)
sstables: introduce sstable::get_max_local_deletion_time
sstables: remove unnecessary copy in time series strategies
sstables: change return value type of get_fully_expired_sstables
dtcs: make code to extract non expired tables faster
sstables: add has_correct_max_deletion_time to sstable
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