Hi there, Our enterprise app is comprised of two major tiers -- a business layer and a service layer. The SL entities represent our core systems, and the BL entities represent business concepts such as customers and items, and there's a controller for each layer. When objects are needed they are instantiated by the controller and cached into persistent memory (ie, lazy load). To keep RAM utilization to a minimum, we load data into the objects only as needed, too. Every get() method has a corresponding load() method which is in charge of requesting data from the service layer. So, the objects get "heavier" as they stick around, but it means less overhead in terms of instantiation. BL entities are destroyed by the BL controller upon completion of any add(), edit(), or remove() transaction. We also have a scheduled task which runs on the side -- it manages a TTL value for the entities based on a datetime value embedded in each entity upon instantiation as well as % available RAM on the server. The less RAM available, the shorter the TTL. This way no one slips through the cracks and we don't max out the memory. On average we have about 6000 object instances in RAM at any given time representing customers, items, categories, etc. If we didn't run a model like this we'd probably have a dozen machines in production in order to support all of our sites, instead of just one. I also recommend if you are thinking about exposing your model as a web service, that you create a lightweight "listener" CFC to function as a middle man between clients and the model. Give it one method called something like "processRequest" and have it collect/pass the actual method name and data container(s) to a persistent controller object for processing. Matt Matthew Drayer Development Manager HCPro, Inc. Marblehead MA [EMAIL PROTECTED] -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Nando Sent: Sunday, February 04, 2007 10:07 AM To: [email protected] Subject: Re: [CFCDEV] How many objects is too many?
Jaime,
My line of thinking here is pretty simple, but i think it's in
line with best practice in CF.
If you simply need to display the data to the user (probably as
a list), use cfquery, a ColdFusion query object. If your users need to
work with the data, then go with business objects, DAO's, etc.
The simple fact of the matter is that a user will not be able to
edit 1000's of entities at the same time. I see the usefulness of an
object most clearly when you need to both maintain state and manipulate
the data, during an editing operation for instance. And i don't see the
possibility of needing to instantiate hundreds of objects in one go
unless you're working with data, specifically a list of records.
As far as your service layer goes, well, you're probably going
to instantiate that and cache it in application scope, using lazy
loading wherever possible. Practically, if you've got 100's of objects
in your service layer, i'm pretty sure they won't all be needed on the
first page load.
Another possible way of minimizing the overhead of object
creation is to represent the data packets only as an array of structs if
you're more comfortable with that rather than a query object, and
populating a full blown business object as necessary from the array of
structs.
Translating that to the world of transfer, at it's current
level, means to me that transfer isn't well suited to display lists, for
instance. Better to use your own gateway for that and return a query
object, possibly caching it with your own mechanism if needed. Or use
the new "Transfer Query Language" feature Mark is working on instead of
your own gateway.
I'm sure your use cases are more complex than i've represented
them here talking about lists and edit operations, but as far as i know,
this is the general approach to use in CF for performance reasons.
Jaime Metcher wrote:
Hi,
When you're modelling your application, how much
attention do you pay to minimizing the number of objects instantiated?
Obviously CF has a higher object creation overhead than some other
languages. OTOH, the gist of much OO practice (and many patterns) is to
create lots of fine grained objects. I often read that a typical noob
error is creating too few objects with too many responsibilities.
So, how often do you find yourself thinking "well, in
Java or Smalltalk I'd do xyz, but in CF I'd better not because I'd end
up with too many objects"? Which is another way of asking to what
extent we need to modify existing OO practices to allow for CF's
limitations.
A couple of points of reference:
1. This post was prompted by a discussion with Mark
Mandel on the transferdev list. I'd spotted an issue purely because of
the massive slowdown that occurred when 700 objects were inadvertently
created. That issue has been resolved, but it left me wondering, if I
can't instantiate 700 objects how many can I create? 10? 50? This has
huge implications for how we architect our apps.
2. I have a Dolphin Smalltalk image that, from a fresh
install, reports instantiating 160,000 objects. Obviously with an
object system this slick you don't worry much about throwing in a few
hundred more. Given that CF's comfort zone is probably a couple of
orders of magnitude lower, maybe a lot of the standard advice on OO
design just doesn't apply to CF?
Any thoughts appreciated.
Jaime Metcher
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