[wildfly-dev] Pooling EJB Session Beans per default

[Bill Burke]

On 8/6/2014 10:50 AM, Andrig Miller wrote:
>
>
> ----- Original Message -----
>> From: "Radoslaw Rodak" <rodakr at gmx.ch>
>> To: wildfly-dev at lists.jboss.org
>> Sent: Tuesday, August 5, 2014 6:51:03 PM
>> Subject: Re: [wildfly-dev] Pooling EJB Session Beans per default
>>
>>
>> Am 06.08.2014 um 00:36 schrieb Bill Burke <bburke at redhat.com>:
>>
>>>
>>>
>>> On 8/5/2014 3:54 PM, Andrig Miller wrote:
>>>>> 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.
>>>>>
>>>>
>>>> The number per request, while relevant is only part of the story.
>>>>   The number of concurrent requests happening in the server
>>>> dictates the object allocation rate.  Given enough concurrency,
>>>> even a very small number of object allocations per request can
>>>> create an object allocation rate that can no longer be sustained.
>>>>
>>>
>>> I'm saying that the number of concurrent requests might not dictate
>>> object allocation rate.  There are probably a number of allocations
>>> that
>>> happen after the EJB instance is obtained.  i.e. interception
>>> chains,
>>> contexts, etc.   If StrictMaxPool blocks until a new instance is
>>> available, then there would be less allocations per request as
>>> blocking
>>> threads would be serialized.
>>>
>>
>> Scenarion 1 )
>> ------------------
>> Let say we have a pool of 100 Stateless EJBs and a constant Load of
>>   50 Requests per second  proceeded by 50 EJBs from the pool in one
>> second.
>> After 1000 seconds how many new EJB Instances will be created having
>> a pool? answer 0 new EJBs  worst case 100 EJB’s in pool… of course
>> object allocation is much higher as of course 1 EJB call leads to
>> many Object from one EJB  but…let see situation without pool.
>>
>> 50 Request/s * 1000 seconds = worst case 50’ 000 EJB Instances on
>> Java heap where 1 EJB might have many objects…   as long as Garbage
>> Collection was not triggered… which sounds to me like faster filling
>> JVM heap and having ofter GC probable depending on GC Strategy.
>>
>> Scenarion 2)
>> ------------------
>> Same as before,  Load is still 50 Requests  per second BUT EJB Method
>> call takes 10s.
>> after 10s we have 500 EJB Instances without pool, after 11s  550 - 10
>> = 540EJB Instances , after 12s  580 EJBs … after some time very bad
>> perf…full GC …and mabe OutOfMemory..
>>
>> So… performance advantage could also turn in to disadvantage :-)
>>
>>
>>> Whoever is investigating StrictMaxPool, or EJB pooling in general
>>> should
>>> stop.  Its pointless.
>>
>> Agree, pools are outdated…. but something like WorkManager for min,
>> max Threads or even better always not less the X idle Threads would
>> be useful :-)
>>
>> Radek
>>
>
> The scenarios above are what is outddated.  Fifty requests per second isn't any load at all!  We have 100's of thousands of clients that we have to scale to, and lots more than 50 requests per second.
>
What you mean to say is that you need to scale to 100's of thousands of 
clients on meaningless no-op benchmarks. :)  I do know that that old 
SpecJ Java EE benchmarks artifically made EJB pooling important as 
process intensive calculation results were cached in these instances. 
But real-world apps don't use this feature/anti-pattern.

Also however crappy it was, I did implement an EJB container at one time 
in my career.  :)  I know for a fact that there are a number of 
per-request internal support objects that need to be allocated.  Let's 
count:

* The argument array (for reflection)
* Each argument of the method call
* The response object
* Interceptor context object
* The interceptor context attribute map
* EJBContext
* Subject, Principal, role mappings
* Transaction context
* The message object(s) specific to the remote EJB protocol

Starts to add up huh?   I'm probably missing a bunch more.  Throw in 
interaction with JPA and you end up with even more per-request objects 
being allocated.  You still believe pooling one EJB instance matters?

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