Hi folks,

Just jotting down some issues with the JobManager over noticed over the
last few days:
1. min-threads in serviceengine.xml is never exceeded unless the job count
in the queue exceeds 5000 (or whatever is configured).  Is this not obvious
to anyone else?  I don't think this was the behavior prior to a refactoring
a few years ago.
2. The advice on the number of threads to use doesn't seem good to me, it
assumes your jobs are CPU bound when in my experience they are more likely
to be I/O bound while making db or external API calls, sending emails etc.
With the default setup, it only takes two long running jobs to effectively
block the processing of any others until the queue hits 5000 and the other
threads are finally opened up.  If you're not quickly maxing out the queue
then any other jobs are stuck until the slow jobs finally complete.
3. Purging old jobs doesn't seem to be well implemented to me, from what
I've seen the system is only capable of clearing a few hundred per minute
and if you've filled the queue with them then regular jobs have to queue
behind them and can take many minutes to finally be executed.

I'm wondering if anyone has experimented with reducing the queue the size?
I'm considering reducing it to say 100 jobs per thread (along with
increasing the thread count).  In theory it would reduce the time real jobs
have to sit behind PurgeJobs and would also open up additional threads for
use earlier.

Alternatively I've pondered trying a PriorityBlockingQueue for the job
queue (unfortunately the implementation is unbounded though so it isn't a
drop-in replacement) so that PurgeJobs always sit at the back of the
queue.  It might also allow prioritizing certain "user facing" jobs (such
as asynchronous data imports) over lower priority less time critical jobs.
Maybe another option (or in conjunction) is some sort of "swim-lane"
queue/executor that allocates jobs to threads based on prior execution
speed so that slow running jobs can never use up all threads and block
faster jobs.

Any thoughts/experiences you have to share would be appreciated.


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