You are absolutely right in that the round trip to the database is going to consume more time for the life of the user request than is a sequence of reflection-based calls. That will always be the bottleneck in systems that don't have any kind of intelligent middle-tier cache - but wait, there's more!
Entity EJBS are just that (a cache) aren't they? Through intelligent caching and good design of our applications, we're able to avoid the extra knocks on the database if the entity of our type with our PK has already been loaded. This, in my mind, is one of the chief advantages of using Entity Beans; throughput. This throughput will definitely be impacted negatively if there are several reflection calls for each user request as the system comes under (and maintains) load. Furthermore, although the bottleneck is clearly the round trip to the database for the hydration/storage of data, the time it takes to get to the point of JDBC query invocation will be effected negatively if reflection is used - this effect becomes more pronounced as the system comes under heavy load. The sooner the JDBC query starts, the sooner it will finish.
I would also note that 'optimizing away' performance issues due to reflection (assuming that the core of the system is based on reflection) is MUCH easier to type than it is to implement. If we see the train coming now, why don't we get out of the way...now?
Best,
John C. Dale
Professional Services
Compuware
Aaron Mulder wrote:
First of all, can we agree that microbenchmarks are dangerous? But all that aside, try 1 million HTTP requests, or 1 million iterations of a JDBC query, and then provide a ratio between JDBC/HTTP time and reflection time. If you can perform a million requests of either type in 30 seconds I'd be shocked, and that's two orders of magnitude.IMHO, reflection is something that can be optimized away later, once it becomes the bottleneck on performance. I don't think we need to avoid it from the outset, because I don't think it will be the bottleneck at the outset. Aaron On Sat, 9 Aug 2003, John C. Dale wrote:I'm concerned about your mention of reflection. I really like reflection, and think it has many useful applications in the application development space, but should be kept out of any runtime application that has stringent scalability and performance requirements. Although reflection allows an incredibly generic way to solve many difficult problems, and really opens the door to completely grandios perfectly idealistic genericititousness ;) , a straight-forward OO approach to solving the problems would 1) be faster and 2) be easier to read and maintain. I've seen reflection based approaches work, and I've seen them bomb. One might argue that in a container based system that will eventually support clustering and scalability doesn't have to worry about savoring individual CPU cycles that might be expended needlessly with a reflection-based design. Just add more hardware and the user experience will be perpetually preserved. I would argue, however, that the development community will be able to make better use of the product if the rate at which additional hardware purchases becomes necessary decreases. The philosophy, IMHO, should be to solve the problems at hand with straight-forward OO solutions, and not to focus so much on being generic and supporting n * infinity solutions up-front. Using things like the Policy/Strategy pattern at well-selected locations will afford the opportunity for pluggability without compromising maintainability and performance. Here are some dramatic results: *Direct:* public void init() { customer = new Customer(); } public void run() { customer.work(); } *Interface (Polymorphism):* public void init() { customer = new Customer(); } public void run() { Person person = (Person) customer; person.work(); } *Reflection:* public void init() { customer = new Customer(); try { method = customer.getClass().getMethod("work", new Class[0]); } catch (Exception e) { } params = new Object[0]; } public void run() { try { method.invoke(customer, params); } catch (Exception e) { } } With 1000000 of the above code, here were the results: JDK DirectTest InterfaceTest ReflectionTest *Sun 1.4* 52 ms 54 ms 543 ms *Sun 1.4 -server* 26 ms 56 ms 279 ms *Sun 1.3* 124 ms 128 ms 2168 ms *Sun 1.3 -server* 41 ms 58 ms 2012 ms *IBM 1.3* 75 ms 78 ms 2134 ms Reflection will significantly effect the performance of the system and should be avoided for any runtime operations. Where it should and could definitely be applied is with the dynamic generation and compilation of code, or generation of metadata. Otherwise, even at the recommendation of Sun, it should be avoided for runtime operations. Best, John C. Dale Leo Simons wrote:Jason Dillon wrote:PS. Can someone write up something about the current state of the major component containers out there with a feature blurb... no soap boxes, just the facts jack.What, no soap boxes? How on earth can anyone comply with that? ;) No wait, you weren't asking me anyway, were you. Ah, e-mail already typed. Bummer. = My Opinion = You should *not* be evaluating component containers. You should save this discussion for a later date and just code your way to 1.0. The basic design idea overview below should show that most of the architectural concepts behind all these containers are very similar. I've been experimenting (no, I will not plug it, you will just get confused) with some reflection that will allow any component written for any of the below to run in any of the other containers, and that is feasible, straightforward and performant. So write your components to plug in whatever you have, do a nice IoC, SoC, SAI, AOP setup, and you will be able to defer refactoring around an external container until much later. But that's my opinion, and I have now said it three times, and your a responsible adult (yep, its a guess, you could also be 11 years old :D). Switching soapbox mode off. = Disclaimer = Comparing component containers is comparing apples with pears. Avalon is by far the biggest 'generic' project at the moment, for example, but recent developments utilize AOP and interceptor architecture to support a much 'lighter' container-component api and contract. Indeed, picocontainer was started by an avalon elder from the firm belief that things should be simpler and smaller. So to actually evaluate all this stuff, you really should spend a day or so delving into the websites and the code of all these projects, and backing tech like nanning (nanning.codehaus.org) and aspectj (www.aspectj.org). I would start by looking at pico/nano and xwork, then take a look at the tutorials for avalon-merlin. The other projects have a smaller community atm, and I tend to value community size and vibe. Furthermore, I have strong opinions about stuff, and allegations to various projects, hence this is not an objective overview, even though I tried to make it somewhat objective. = Features/ design idea shorthands = IoC = Inversion of Control, the idea that an application is controlled from the top down SoC = Seperation of Coccerns, the idea that a class (aspect) should do one job and do it well SAI = Seperation of API from Implementation, the idea that you define and code to work interfaces AOP = Aspect Oriented Programming, mostly lightweight nowadays where you add a chain of interceptors around a method call that can handle orthogonal concerns DecP = Declarative Programming, where you use a declarative-style language (usually xml) to determine things like component wiring (ie your average tomcat config file, generalized) EBP = Event Based Programming, basically making the inter-object method call asynchronous and encapsulating such a call into some kind of event object that can be queued, modfied, etc = No particular order, incomplete list = http://wiki.opensymphony.com/space/XWork - IoC, SoC, SAI, AOP, DecP, EBP. Nearing 1.0 release. Used in webwork2 (a competitor to struts). EBP very basic only. Lean and mean, but not mature and some client-server web-layer specific assumptions. Don't like the XXXAware interfaces. Very vibrant and active community and many famous peeps with J2EE experience around at opensymphony. http://www.picocontainer.org/ and http://www.nanocontainer.org/ - IoC, SoC, SAI, AOP, DecP. 1.0 beta releases. Lean and mean and very extensible and embeddable, developed by smart XP peeps, some stuff already in use in some apps, but otherwise pretty much alpha. I love picocontainer and the way they're doing the project. The dev community is intentionally kept small atm, but many peeps are watching this one. http://plexus.codehaus.org/ - IoC, SoC, SAI, DecP. Container supporting avalon-framework components. Used to be yet-another-novel-avalon-container, but I think they're growing to be container-component-contract-agnostic. Corporate backed development. Smart guys, not so much focussed on releases as on getting all the functionality they need (which is a lot) in place. Very much a pragmatic project. http://www.jcontainer.org/ - Not yet public container development (dubbed 'loom' IIRC) by a smart ex-avaloner 'n others. Haven't seen any code yet but my guess is it'll be good. The website says "move along" so you prolly should. http://www.springframework.org/ - haven't looked at in too much depth. Seems similar to nanocontainer and xwork. Think it has one active developer and a beta release. Some smart points made, but too much xml for my taste. Hoping to see some of this rolled into Xwork and/or pico. http://avalon.apache.org/ - IoC, SoC, SAI, DecP, EBP (EBP for fortress only). By far the oldest 'generic container' project. Big committer base, mature codebase, mature ASF project (which can be a good thing and a bad thing ;) rather extensive 'avalon-framework' (comparatively heavy compared to more recent developments) that defines the contracts between a component and a container. Has 3 container projects to consider: avalon-phoenix, a mature microkernel design, avalon-fortress, similar in weight and featureset to something like nanocontainer with a 1.0 release (successor to avalon-ecm, the container used in (among other projects) apache-cocoon), and avalon-merlin, a more recent development which we _seem_ to be converging on as the successor to all other previously produced containers. Merlin is further described in the email by Stephen Mcconnell. Arguably the biggest, most extensive and most dynamic IoC container implementation around (and hence also the most complex). Re: my earlier blurb on 'geronimo and avalon' for more yadayada. http://jakarta.apache.org/commons/sandbox/hivemind - haven't looked at in much detail, but seems very similar in scope and setup to avalon at first glance. Framework being refactored out of hibernate, one developer, still in alpha with no releases I think. No offense to Howard intended, but I think he's cut himself a rather big piece of the puzzle to recode from scratch at once. But I am an uninformed whiner, so I'm not going to comment further in the hope that Howard will just eventually see the light and direct his energy towards collaboration with the avalon peeps :P I am spending too much time on writing messages to this mailing list (it is nearly 3am over here). I promise this is the last message from me for two weeks :D g'night, - Leo
