Steven,
yes we have not done a great job of documenting nor auto-tuning the reserved thread pool. The reserved thread pool was something forced onto us be the more difficult scheduling demands of HTTP2 and we didn't fully understand all the implication when it was introduced, thus we could not well document it. However, with the next release (9.4.8) we are reaching a happier point where lazy allocation of reserved threads means a natural level is reached, plus we have a ThreadPoolBudget mechanism now to warn if a pool is over allocated. So we do need to spend more time writing these solutions. With regards to sharing threadpools and schedulers. Yes there can be benefits of sharing these between multiple clients. There can even be benefits of using the server pools/schedulers. But there also can be contention issues if you have large machines with many CPUs. So there is no silver bullet solution that will work for all applications. I strongly advise trying some alternate configurations and benchmarking them. cheers On 1 November 2017 at 04:34, Steven Schlansker <[email protected]> wrote: > I'm nearing delivery of my new awesome Jetty Based Proxy Thing 2.0 and > deployed it to one of our test environments. > > Due to braindead vendor load balancers and some internal testing needs, > the Jetty when deployed to this environment needs to have 6 (!) connectors. > > At first, it ran fine -- but after serving (light) load for a few minutes > the > server would start to hang more and more connections indefinitely, until > eventually > idle timeout. Eventually the entire thing wedges and only the most > trivial of requests > finish. > > After quite a bit of debugging, I realized that each connector seems to be > starting up a ManagedSelector and ReservedThreadExecutor. These each > "reserve" > threads from the pool in that they block waiting for work that needs to > get handled > immediately. > > I'd started with 20 threads, figuring that would be enough for a test > environment with > only a couple of requests per second. > > Thus, very few (or no) pool threads are ever available to do the actual > normal priority work. > However the EWYK scheduler still seems to make partial progress (as long > as tasks do > not hit the queue, they keep going) -- but anything that gets queued hangs > forever. > The server ends up in a very confusing partially working state. > > Reading through the docs, all I could find is this one liner: > "Configure with goal of limiting memory usage maximum available. Typically > this is >50 and <500" > > No mention of this pretty big pitfall. If the tunable was strictly > performance, that might be just > fine -- but the fact that there's liveness concerns makes me think that we > could do better. > > At least a documentation tip -- "each connector reserves 1 ManagedSelector > + 1/8 * #CPU reserved threads by default" > would be welcome, but even better would be if the QueuedThreadPool could > somehow assert that the configuration > is not writing reserved thread checks that it can't cash. > > WDYT? > > > Relatedly, my proxy reaches out to many backends. Each backend may have > its own configuration for some > high level tuneables like timeouts and maximum number of connections. So, > each one gets its own HttpClient. > > This ends up creating a fair number of often "global" resources -- threads > mostly. > > Is it recommended practice to share these? i.e. create one Executor and > Scheduler to share among > HttpClient instances, or go even further and just take them from the > Server itself? > > Seems like it might have some benefits -- why incur a handoff from the > server thread to the client thread > when you're just ferrying data back and forth -- however given my > adventures with sizing just the server > thread pool I worry I might get myself in trouble. But if it's just a > matter of sizing it appropriately... > > > Thanks for any guidance! > Steven > > _______________________________________________ > jetty-users mailing list > [email protected] > To change your delivery options, retrieve your password, or unsubscribe > from this list, visit > https://dev.eclipse.org/mailman/listinfo/jetty-users > -- Greg Wilkins <[email protected]> CTO http://webtide.com
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