after compound set is introduced, select_sstable_runs() will no longer
work because the sstable runs live in sstable_set, but they should
actually live in the sstable_set being written to.
Given that runs is a concept that belongs only to strategies which
use partitioned_sstable_set, let's move the implementation of
select_sstable_runs() to it.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20210312042255.111060-2-raphaelsc@scylladb.com>