[wildfly-dev] Pooling EJB Session Beans per default

[Radoslaw Rodak]

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