presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/metadata/ShardCleaner.java/ShardCleaner/startJobs
class ShardCleaner:    private void startJobs()
    {
        if (coordinator) {
            startTransactionCleanup();
            if (backupStore.isPresent()) {
                scheduleBackupCleanup();
            }
        }

        // We can only delete local shards if the backup store is present,
        // since there is a race condition between shards getting created
        // on a worker and being committed (referenced) in the database.
        if (backupStore.isPresent()) {
            scheduleLocalCleanup();
        }
    }