[MESOS-1199] Subprocess is "slow" -> gated by process::reap poll interval

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.18.0
• Sprint: Mesos Q3 Sprint 6
• Story Points: 1
• Assignee: Ian Downes
• Reporter: Ian Downes
• Shepherd: Ian Downes
• Created: 08/Apr/14 18:20
• Updated: 31/Jul/15 00:58
• Resolved: 26/Sep/14 17:22

Description

Subprocess uses process::reap to wait on the subprocess pid and set the exit status. However, process::reap polls with a one second interval resulting in a delay up to the interval duration before the status future is set.

This means if you need to wait for the subprocess to complete you get hit with E(delay) = 0.5 seconds, independent of the execution time. For example, the MesosContainerizer uses mesos-fetcher in a Subprocess to fetch the executor during launch. At Twitter we fetch a local file, i.e., a very fast operation, but the launch is blocked until the mesos-fetcher pid is reaped -> adding 0 to 1 seconds for every launch!

The problem is even worse with a chain of short Subprocesses because after the first Subprocess completes you'll be synchronized with the reap interval and you'll see nearly the full interval before notification, i.e., 10 Subprocesses each of << 1 second duration with take ~10 seconds!

This has become particularly apparent in some new tests I'm working on where test durations are now greatly extended with each taking several seconds.

Issue Links

• is related to: MESOS-1757 Speed up the tests