yadage: starting times of jobs are missing in the database

[mdonadoni]

The starting times of jobs are not saved in the database. Note that, instead, finishing times are correctly persisted.

How to reproduce:

1. Execute one of the demo yadage workflows
2. Connect to the database kubectl exec -it deployment/reana-db -- psql -U reana reana
3. Check that started_at is not set to any value

reana=# select id_, started_at, finished_at, status from __reana.job;
                 id_                  |         started_at         |        finished_at         |  status  
--------------------------------------+----------------------------+----------------------------+----------
 bb50a2cc-0496-4d7d-9a70-e016e1bba386 |                            | 2022-10-07 08:20:17.793953 | finished
 14dc7493-91be-4eba-9e70-4f82ba34ad4d |                            | 2022-10-07 08:20:02.482219 | finished

[mdonadoni]

This is due to the rate at which the workflow engine polls the status of the job:

reana-workflow-engine-yadage/reana_workflow_engine_yadage/config.py

Lines 19 to 21 in f51a301

	WORKFLOW_TRACKING_UPDATE_INTERVAL_SECONDS = 15
	LOG_INTERVAL_SECONDS = 15

If a job is fast enough, it can happen that its status goes from created to finished, without ever being running. The started_at time is thus never set (source):

@event.listens_for(Job.status, "set")
def job_status_change_listener(job, new_status, old_status, initiator):
    """Job status change listener."""
    if new_status != old_status:
        from .database import Session

        if new_status in [
            JobStatus.finished,
            JobStatus.failed,
        ]:
            job.finished_at = datetime.now()
        elif new_status in [JobStatus.running]:
            job.started_at = datetime.now()

        Session.commit()