Tim Armstrong created IMPALA-9457:
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Summary: Lazy start of disk threads in I/O manager
Key: IMPALA-9457
URL: https://issues.apache.org/jira/browse/IMPALA-9457
Project: IMPALA
Issue Type: Improvement
Components: Backend
Reporter: Tim Armstrong
Currently DiskIoMgr starts all the I/O threads upfront for all supported
filesystems. This means there are 100s of idle threads in most impalads that
never do anything. It would be sensible to start the threads for a disk only
when the first range is submitted. It's not immediately obvious where the best
place to do this is. A couple of ideas:
* Try to do it in ScheduleContext in a lightweight way, e.g. check an atomic to
see if it's been initialised, then acquire a lock and create the threads if
needed. Propagating the status if thread creation fails may be the tricky part
* Start up one thread per disk, so I/O can always make progress, and start an
extra thread per disk each time a range is pulled off the queue in
DiskQueue::GetNextRequestRange() so that the number of threads ramps up as scan
ranges are submitted. It could potentially be clever and try to track how many
threads are parked and only create new threads if 0 threads are parked.
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