The motivation behind this change to free up disk space as early as possible.
The reason is that snapshot locks the space of all SSTables in the snapshot,
and deleting form the table, for example, by compaction, or tablet migration,
won't free-up their capacity until they are uploaded to object storage and deleted from the snapshot.
This series adds prioritization of deleted sstables in two cases:
First, after the snapshot dir is processed, the list of SSTable generation is cross-referenced with the
list of SSTables presently in the table and any generation that is not in the table is prioritized to
be uploaded earlier.
In addition, a subscription mechanism was added to sstables_manager
and it is used in backup to prioritize SSTables that get deleted from the table directory
during backup.
This is particularly important when backup happens during high disk utilization (e.g. 90%).
Without it, even if the cluster is scaled up and tablets are migrated away from the full nodes
to new nodes, tablet cleanup might not free any space if all the tablet sstables are hardlinked to the
snapshot taken for backup.
* Enhancement, no backport needed
Closesscylladb/scylladb#23241
* github.com:scylladb/scylladb:
db: snapshot: backup_task: prioritize sstables deleted during upload
sstables_manager: add subscriptions
db: snapshot: backup_task: limit concurrency
sstables: directory_semaphore: expose get_units
db: snapshot: backup_task: add sharded sstables_manager
database: expose get_sstables_manager(schema)
db: snapshot: backup_task: do_backup: prioritize sstables that are already deleted from the table
db: snapshot-ctl: pass table_id to backup_task
db: snapshot-ctl: expose sharded db() getter
db: snapshot: backup_task: do_backup: organize components by sstable generation
db: snapshot: coroutinize backup_task
db: snapshot: backup_task: refactor backup_file out of uploads_worker
db: snapshot: backup_task: refactor uploads_worker out of do_backup
db: snapshot: backup_task: process_snapshot_dir: initialize total progress
utils/s3: upload_progress: init members to 0
db: snapshot: backup_task: do_backup: refactor process_snapshot_dir
db: snapshot: backup_task: keep expection as member
d9853efa7c