Off-strategy SSTables are SSTables that do not conform to the invariants
that the compaction strategies define. Examples of offstrategy SSTables
are SSTables acquired over bootstrap, resharding when the cpu count
changes or imported from other databases through our upload directory.
This patch introduces a new class, sstable_directory, that will
handle SSTables that are present in a directory that is not one of the
directories where the table expects its SSTables.
There is much to be done to support off-strategy compactions fully. To
make sure we make incremental progress, this patch implements enough
code to handle resharding of SSTables in the upload directory. SSTables
are resharded in place, before we start accessing the files.
Later, we will take other steps before we finally move the SSTables into
the main directory. But for now, starting with resharding will not only
allow us to start small, but it will also allow us to start unleashing
much needed cleanups in many places. For instance, once we start
resharding on boot before making the SSTables available, we will be able
to expurge all places in Scylla where, during normal operations, we have
extra handler code for the fact that SSTables could be shared.
Tests: a new test is added and it passes in debug mode.
Signed-off-by: Glauber Costa <glauber@scylladb.com>
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