At the moment, it's not possible to know how many compaction are needed for
compaction strategy to be satisfied. It's not possible to know exactly the
number of pending compaction, but the strategy can provide an estimation.
For size tiered, it's based on number of sstables in each bucket. By dividing
bucket size by max threshold, we get number of compaction needed to compact
that single bucket.
For leveled, it's about the number of sstables that exceeds the limit in
each level.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <e209e52f6159ee274a8358b69961a7c0ce357f7d.1467667054.git.raphaelsc@scylladb.com>
Allow compaction_strategy to create a container for sstables that is
optimized for the strategy.
Most compaction_strategies return bag_sstable_set; leveled compaction
returns the specialized partitioned_sstable_set.
partitioned_sstable_set assumes that sstable are mostly partitioned along
the token range: only a few sstables will be needed to access a particular
token. It is implemented as an interval_map.
bag_sstable_set is a generic sstable_set implementation: it assumes nothing
about the sstables. It is implemented as a vector, and any select will
return the entire sstable set.
sstable_set abstracts the notion of a container of sstables, allowing
different compaction strategies to supply their own implementation. The
intended user is leveled compaction strategy; since it partitions sstables,
it can quickly restrict the number of sstables that participate in a query
by looking at the min/max partition key.
sstable_set also maintains an internal lw_shared_ptr<sstable_list>,
in parallel with the abstract container. This is to support
column_family::get_sstable(), which returns a lw_shared_ptr<sstable_list>
which must be anchored somewhere if it is not saved at the caller side,
as it isn't in most current callers.
sstable_list is now a map<generation, sstable>; change it to a set
in preparation for replacing it with sstable_set. The change simplifies
a lot of code; the only casualty is the code that computes the highest
generation number.
It was discussed that leveled strategy may not benefit from parallel
compaction feature because almost all compaction jobs will have similar
size. It was also found that leveled strategy wasn't working correctly
with it because two overlapping sstable (targetting the same level)
could be created in parallel by two ongoing compaction.
Fixes#1293.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <60fe165d611c0283ca203c6d3aa2662ab091e363.1464883077.git.raphaelsc@scylladb.com>
