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 :-)
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.
It’s not about size of load unit, it’s about behavior with and without pool with load over period of time with side effects :-) Just Number of Clients doesn’t matter so much… but number concurrent requests from the clients per time unit...
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