[jboss-as7-dev] Limiting Server Thread Usage

[Carlo de Wolf]

I'll illustrate how inverting the pool complements the big thread pool.

On 09/16/2011 08:35 AM, Stuart Douglas wrote:
> What about if we had 1 underlying thread pool that provides all the threads, and then subsystems use a custom executor that provides a 'view' of this underlying thread pool.

+1. We need this to guard the total number of threads.
> So for instance we have the main thread pool that has a max of 25 threads, we could then give the EJB remote invocation pool is then given an executor that can use a maximum of 10 threads from the pool.

If we just stick to EJB, this means that those 10 (or more) threads 
become an extremely precious resource. Any time one of these threads 
blocks we're wasting precious cycles. So instead of blocking for 
resources to become available we should only pick up a request that can 
proceed without blocking. Further more we should prioritize jobs that 
require lesser work, this is called 'maximum throughput scheduling'. 
Note that there are more criteria (like max wait time, queue size etc) 
that need to be worked in, but that should be expressible in a formula 
the drives a 'priority queue'.
> This would also allow you to give these executors a priority, so for example you could give the web subsystem thread pool a higher priority to make sure that web requests always get handled first.

We should not put a maximum on a 'subsystem' pool, because that would 
not allow it to fully utilize the total pool if the others are idle. 
Better to leave a minimum on hot standby.

Carlo
> I'm not really sure how well this would work, but I just thought I would put it out there.
>
> Stuart
>
> On 15/09/2011, at 3:53 AM, Jason T. Greene wrote:
>
>> Moving to a new thread.
>>
>> The big problem we run into with this is that almost every application
>> of a thread pool that we have needs to be highly tailored to its usage
>> to get the most optimal performance. So we end up with quite a few
>> different pools and it becomes difficult to impose a server wide limit.
>>
>> There however some potential strategies we could take. Although I am
>> unsure as to how the overall effectiveness would be:
>>
>> 1. Sharing idle threads between pools
>> 2. Force everything to go through a special blocking thread factory via
>> instrumentation of java.lang.Thread. Any attempt to allocate over the
>> max would lead to thread reclamation attempts and finally blocking until
>> a timeout is reached.
>> 3. Some kind of auto-tuning weighting model. If the max total threads is
>> N, force all thread pools to use a percentage of N, potentially based on
>> establishing current config value divided by combined total.
>>
>> One thing I wonder though is if cloud providers are "barking up the
>> wrong tree"? It seems a better limitation of an application is raw CPU
>> clock time and max memory usage. How they split that time into threads
>> doesn't really affect the scalability of the physical server, it's all
>> virtual process performance (who cares if someone wastes time context
>> switching?).
>>
>> On 9/14/11 10:39 AM, Scott Stark wrote:
>>> The other big cross cutting concern is controlling the total number of
>>> threads in use by the application server. When running under a
>>> constrained environment that uses something like pam_limits module to
>>> control how many process(==java threads) a user can have, it is
>>> difficult to know what the server max thread usage is right now.
>>>
>> -- 
>> Jason T. Greene
>> JBoss AS Lead / EAP Platform Architect
>> JBoss, a division of Red Hat
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