[wildfly-dev] Pooling EJB Session Beans per default

[Bill Burke]

On 8/5/2014 10:51 AM, Jason Greene wrote:
>
> On Aug 5, 2014, at 9:32 AM, Bill Burke <bburke at redhat.com> wrote:
>
>>
>>
>> On 8/5/2014 10:15 AM, Jason Greene wrote:
>>>> Those silly benchmarks, are indeed silly.  Any workload that doesn't actually do anything with the requests is not very helpful.  You can be really fast on them, and be really slow on a workload that actually does something.  We have already seen this in one case recently.
>>>
>>> It’s all about precision, and limiting variables. I know its fun to criticize micro benchmarks (obviously micro is indeed relative because a great deal of processing goes on even when you have EJB and HTTP requests that don’t do much), however micro benchmarks, provided they are measured correctly, are quick to run and make it easy to tell what you have to fix. Large gigantic apps on the other hand are difficult to analyze, and do not necessarily represent activity that a differently architected app would show. To use an example, if you have pattern matching code, and you want it to be fast, it’s much easier (and accurate) to benchmark the pattern matching code then it is to benchmaark a full EE app that happens to use pattern matching in a few places.
>>>
>>> Arguing against targeted benchmarks is like arguing that you should never write a test case, because only real production load will show problems…. To some extent thats true, but that doesn’t mean that the problems you catch in simulations won’t affect production users.
>>>
>>
>> I'm more worried about focus rather than the actual benchmarks considering how resource strapped every project seems to be.  I'd like to see a discussion started on what are the most important and *ripe* areas for optimization and then have the performance team validate and make recommendations on any priority list that this discussion generates.
>
> The pooling concerns (aside from the occasional expensive post constructs) actually came from a large app/benchmark that the perf team was testing, and they were seeing an optimized strict max pool outperform no pooling at all, and it wasn’t post construct. Their theory is/was GC pressure, because this benchmark/app spends a lot of time in GC, and they see higher GC activity with no pooling. It’s possible it could be an indirect difference though, like the fact that strict max pool acts as a throttle might prevent the system from degrading as a result of no longer being able to keep up with the benchmark load.
>

Its a horrible theory. :)  How many EJB instances of a give type are 
created per request?  Generally only 1.  1 instance of one object of one 
type!  My $5 bet is that if you went into EJB code and started counting 
how many object allocations were made per request, you'd lose count very 
quickly.   Better yet, run a single remote EJB request through a perf 
tool and let it count the number of allocations for you.  It will be 
greater than 1.  :)

Maybe the StrictMaxPool has an effect on performance because it creates 
a global synchronization bottleneck.  Throughput is less and you end up 
having less concurrent per-request objects being allocated and GC'd.


> Another possibility to look into is that I see we do:
>     interceptorContext.setContextData(new HashMap<String, Object>());
>
> *AND*
>
>      private Map<Object, Object> instanceData = new HashMap<Object, Object>();
>
>
> Aside from the unnecessary overhead, since JDK7, HashMap construction uses the murmur algorithm which requires using a random number generation under global locking. There were plans to optimize this, but it might not be in JDK7 yet. In a few places we use alternative map implementations to work around the issue.
>



IMO, it is more likely that most projects haven't gone through the level 
of refactorings that performance-focused projects like Undertow have 
gone through.  I'll put another $5 bet down that only the Wildfly family 
of projects under you and DML have gone through any real performance 
analysis and optimizations.  Just think of all the crappiness that is 
happening in the security layer alone!

Also, any optimizations projects have done are probably focused on speed 
and throughput which generally is at the expense of memory.

-- 
Bill Burke
JBoss, a division of Red Hat
http://bill.burkecentral.com