A possible improvement to the `metrics_writes` and `log_pack`

Right now we select from the `metrics_writes` into a temporary table.

Does "select for update" make a difference?

Should we mark the rows for deletion instead of deleting them, then drop them with a separated job?

Would it be interesting to use a table that is partitioned by time so that we can work only on the last set of rows, and drop entire partitions altogether when cleaning up?