Chris, Chris: Very valid advice. The importance of good architectural practice cannot be overstressed.
Another link that Daniel and others may find interesting is http://www.ConvergentArchitecture.com - "Convergent Architecture" is a recent book from OMG (Object Management Group) Press and covers MDA (Model Driven Architecture) as the methodology for building model-driven J2EE systems with UML. There are also some useful links under this URL including tutorials, supporting product links and extracts from the book. Happy reading! Robert Thompson, Chris wrote: >Hi Daniel, > >I have read through your recent posts about entity beans, cpu and java >virtual machine capacities, performance etc as we have a tool call Bean-test >that measures EJB performance so I was curious. I sense that you are >learning about what a J2EE application server does, how that works with the >Java Virtual Machine, and how Enterprise JavaBeans work, etc. > >Basically the J2EE application server runs the EJB for you, takes care of >managing all the calls for an EJB, and for container managed persistence >(CMP) also takes care of all the connections from the EJB to the database >where the actual persistent data is stored. The J2EE application server >typically runs within a single Java Virtual Machine process, but it is >really the application server program that handles all the requests to the >EJBs. Each application server vendor will implement things differently but >typically calls to an EJB are managed via queues of the requests, pooling of >available EJB instances to handle those requests, and pooling of connections >to the database. Concurrency then is a notion that multiple instances of an >EJB (i.e. different entity bean instances of the same type) can be executing >a method at the same time. I am not sure what your intended use is where >you would like to eliminate concurrency, but my suggestion is that you look >further into the deployment descriptor settings for entity beans for your >application server to learn more about what you can specify to the >application server how the concurrency should be handled in terms of >limiting the number of concurrent instances and, to add another level of >complexity, how database access is handled in the case of multiple EJB >clients trying to access the same entity bean at the same time. Your >application server vendor should also be able to tell you the hardware and >operating system requirements for running your EJBs at the particular load >you are considering. The Mastering EJB book described on TheServerSide.com >is also a good reference for learning more about how things work >(http://www.theserverside.com/books/masteringEJB/index.jsp). > >Remember that even though the application server can do many good things for >you in terms of providing good performance, you are still responsible for >creating a well architected and implemented implementation that will perform >well. For example your application architecture could have artificial >bottlenecks in it that you could never overcome by changing application >server settings or adding more memory or CPUs. There are prior posts about >EJB access patterns as well as many books and articles available for you to >read about good J2EE architecture design patterns. One place to start might >be the J2EE Blueprints site at http://java.sun.com/blueprints/. > >I hope this helps, > >-Chris Thompson >Bean-test Developer >http://www.empirix.com > >-----Original Message----- >From: daniel legziel [mailto:[EMAIL PROTECTED]] >Sent: Sunday, February 24, 2002 8:48 AM >Subject: entity concurrency problematics > > >Hi all, > >I have a question about concurrency with entity beans. Is concurrency a >notion that depicts (using JMS) simultaneous messages to an entity object or >to the entity's container? In other words is eliminating concurrency at the >object level (by using a message driven beans hub) sufficient or will the >messages jam at the container level? If so what can be used to avoid this? > >Thank's in advance > >Daniel > >_________________________________________________________________ >Chat with friends online, try MSN Messenger: http://messenger.msn.com > >=========================================================================== >To unsubscribe, send email to [EMAIL PROTECTED] and include in the body >of the message "signoff EJB-INTEREST". For general help, send email to >[EMAIL PROTECTED] and include in the body of the message "help". > > =========================================================================== To unsubscribe, send email to [EMAIL PROTECTED] and include in the body of the message "signoff EJB-INTEREST". For general help, send email to [EMAIL PROTECTED] and include in the body of the message "help".
