For tombstone expiration to proceed correctly without the risk of resurrecting
data, the sstable set must be present.
Regular compaction and derivatives provide the sstable set, so they're able
to expire tombstones with no resurrection risk.
Resharding, on the other hand, can run on any shard, not necessarily on the
same shard that one of the input sstables belongs to, so it currently cannot
provide a sstable set for tombstone expiration to proceed safely.
That being said, let's only do expiration based on the presence of the set.
This makes room for the sstable set to be feeded to compaction via descriptor,
allowing even resharding to do expiration. Currently, compaction thinks that
sstable set can only come from the table, and that also needs to be changed
for further flexibility.
It's theoretically possible that a given resharding job will resurrect data if
a fully expired SSTable is resharded at a shard which it doesn't belong to.
Resharding will have no way to tell that expiring all that data will lead to
resurrection because the relevant SSTables are at different shards.
This is fixed by checking for fully expired sstables only on presence of
the sstable set.
Fixes#6600.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20200605200954.24696-1-raphaelsc@scylladb.com>
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