"Initial implementation/transposition of commit log replay.
* Changes replay position to be shard aware
* Commit log segment ID:s now follow basically the same scheme as origin;
max(previous ID, wall clock time in ms) + shard info (for us)
* SStables now use the DB definition of replay_position.
* Stores and propagates (compaction) flush replay positions in sstables
* If CL segments are left over from a previous run, they, and existing
sstables are inspected for high water mark, and then replayed from
those marks to amend mutations potentially lost in a crash
* Note that CPU count change is "handled" in so much that shard matching is
per _previous_ runs shards, not current.
Known limitations:
* Mutations deserialized from old CL segments are _not_ fully validated
against existing schemas.
* System::truncated_at (not currently used) does not handle sharding afaik,
so watermark ID:s coming from there are dubious.
* Mutations that fail to apply (invalid, broken) are not placed in blob files
like origin. Partly because I am lazy, but also partly because our serial
format differs, and we currently have no tools to do anything useful with it
* No replay filtering (Origin allows a system property to designate a filter
file, detailing which keyspace/cf:s to replay). Partly because we have no
system properties.
There is no unit test for the commit log replayer (yet).
Because I could not really come up with a good one given the test
infrastructure that exists (tricky to kill stuff just "right").
The functionality is verified by manual testing, i.e. running scylla,
building up data (cassandra-stress), kill -9 + restart.
This of course does not really fully validate whether the resulting DB is
100% valid compared to the one at k-9, but at least it verified that replay
took place, and mutations where applied.
(Note that origin also lacks validity testing)"
Fixes#98.
702de43ce3