The issue is triggered by compaction of sstables of level higher than 0.
The problem happens when interval map of partitioned sstable set stores
intervals such as follow:
[-9223362900961284625 : -3695961740249769322 ]
(-3695961740249769322 : -3695961103022958562 ]
When selector is called for first interval above, the exclusive lower
bound of the second interval is returned as next token, but the
inclusivess info is not returned.
So reader_selector was returning that there *were* new readers when
the current token was -3695961740249769322 because it was stored in
selector position field as inclusive, but it's actually exclusive.
This false positive was leading to infinite recursion in combined
reader because sstable set's incremental selector itself knew that
there were actually *no* new readers, and therefore *no* progress
could be made.
Fix is to use ring_position in reader_selector, such that
inclusiveness would be respected.
So reader_selector::has_new_readers() won't return false positive
under the conditions described above.
Fixes#2908.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
818830715f