Fixes#23017
When deleting segments while our footprint is over the limit, mainly when recycling/deleting segments after replay (recover boot) we can cause two deletion passes to be running at the same time. This is because delete is triggered by either
a.) replay release
b.) timer check (explicit)
c.) timer initiated flush callback
where the last one is in fact not even waited for. If we are considering many files for delete/recycle, we can, due to task switch, end up considering segments ok to keep, in parallel, even though one of them should be deleted. The end result will be us keeping one more segment than should be allowed.
Now, eventually, this should be released, once we do deletion again, but this can take a while.
Solution is to simply ensure we serialize deletion. This might cause some delay in processing cycles for recycle, but in practice, this should never happen when we are in fact under pressure.
As noted in the issue above, when replaying a large commitlog from an unclean node, we can cause shard 0
db commitlog to reach footprint limit, and then remain there (because we never release segments lower than limit). This is wasteful with diskspace. But deleting segments early here is also wasteful; A better solution is
to simply give the segments to all CL shards, thus distributing the available space.
Closesscylladb/scylladb#23150
* github.com:scylladb/scylladb:
main/commitlog: wait for file deletion and distribute recycled segments to shards
commitlog: Serialize file deletion
2795d83b32