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fdf61d2f7c
before this change, there are chances that the temporary sstables created for collecting the GC-able data create by a certain compaction can be picked up by another compaction job. this wastes the CPU cycles, adds write amplification, and causes inefficiency. in general, these GC-only SSTables are created with the same run id as those non-GC SSTables, but when a new sstable exhausts input sstable(s), we proactively replace the old main set with a new one so that we can free up the space as soon as possible. so the GC-only SSTables are added to the new main set along with the non-GC SSTables, but since the former have good chance to overlap the latter. these GC-only SSTables are assigned with different run ids. but we fail to register them to the `compaction_manager` when replacing the main sstable set. that's why future compactions pick them up when performing compaction, when the compaction which created them is not yet completed. so, in this change, * to prevent sstables in the transient stage from being picked up by regular compactions, a new interface class is introduced so that the sstable is always added to registration before it is added to sstable set, and removed from registration after it is removed from sstable set. the struct helps to consolidate the regitration related logic in a single place, and helps to make it more obvious that the timespan of an sstable in the registration should cover that in the sstable set. * use a different run_id for the gc sstable run, as it can overlap with the output sstable run. the run_id for the gc sstable run is created only when the gc sstable writer is created. because the gc sstables is not always created for all compactions. please note, all (indirect) callers of `compaction_task_executor::compact_sstables()` passes a non-empty `std::function` to this function, so there is no need to check for empty before calling it. so in this change, the check is dropped. Fixes #14560 Signed-off-by: Kefu Chai <kefu.chai@scylladb.com> Closes #14725