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From Joe Baldwin <>
Subject Re: Visibility & Monitoring
Date Thu, 08 Apr 2010 21:49:51 GMT
Hi Michael,

Thank you for your methodical answers.

I suspected that this might be one of my problems, and I am trying to redesign so that I only
filter & order small result lists.

Oops!   OK, this one totally threw me.  Given my understanding of the behavior and usage of
the DataContext is somewhere between "wow" to "hmmm, I didn't know that",   Perhaps I need
to review a primer. :)

But seriously:
Since I am deploying a web-app, my understanding is that in that type of scenario the container
(via the Tomcat CayenneFilter) is instantiating and controlling the DataContext (and I am,
presumably now accessing it via BaseContext.getThreadObjectContext();)  However, beyond that
piece of understanding, I am not sure what to do with it in order to manage objects.

I read your docs once more and it says that the DataContext uses "weak references to store
registered objects".  I *thought* this meant that (assuming I use the default configuration),
that the DataContext would allow the DataObjects to be garbage collected, if there is no reference
(Java Reference) and if I did not implement query caching.

I am confused by reading you Q4 comment and then the "Memory Management Strategy" documentation.

(Note: I am attempting to learn more about Cayenne so that I can optimize (and re-factor)
my code.  I am still uncertain whether I should be implementing caching, not implementing
caching, initiating garbage collection (after freeing objects), or just sitting back and letting
Cayenne DataContext handle it.)


On Apr 8, 2010, at 5:18 PM, Michael Gentry wrote:

> Hi Joe,
> Assuming 2000 products fetched with a paginated query and a page size
> of 50, I believe the answers are ...
> Q1: 2000 hollow objects are created.   Cayenne fetches the primary
> keys of the objects first in a paginated query.
> Q2: Whichever page (or pages) you access in the paginated list will
> fault those objects for that page (grouped by 50 at a time) into
> memory.
> Q3: If you try to filter or sort in-memory, then it will have to fetch
> all of the objects.  Might be better to re-issue a query to the DB.
> Q4: If your list pointers go out-of-scope, but the DataContext is
> still in-scope, then the objects will still be in the DataContext
> until you evict them.
> mrg
> On Thu, Apr 8, 2010 at 4:24 PM, Joe Baldwin <> wrote:
>> Andrus,
>> In this same context, I have a question about what behavior I should expect to see.
>> Let us assume for this scenario:
>> 1. a web deployment with Tomcat, typical webstore pattern
>> 2. 2000-5000 products with an attribute "name"
>> 3. custom search engine built on top of cayenne
>>        a. mostly standard configuration
>>        b. set PageSize to 50
>>        c. using (presumably) default caching
>>        d. custom factory class method used to create a select query
>> 4. a user searches for "guitar" substring in the name field
>> Questions:
>> 1. Based on my tests, it appears that "hollow" objects are created but no faults
are fired. (true?)
>> 2. If I display any product data for a subset less than PageSize, then only <PageSize>
number of objects are faulted (true ?)
>> 3. If I execute "filterObjects" or "orderList" on the resulting list, I assume the
fault is fired for all objects in the list. (true ?)
>> 4. What normally happens to these objects if my list pointers go out of scope?  (Are
they GarbageCollected per Java rules?)
>> (Note: I have not been able to get much visibility in understanding (3) & (4),
but I think my tests show that 1 & 2 are correct.)
>> Joe
>> On Apr 8, 2010, at 12:42 PM, Andrus Adamchik wrote:
>>> BTW, we started on some monitoring hooks inside Cayenne runtime in 3.0 per
, however then it was decided that it'll work much better with the 3.1 DI-based stack. So
this is waiting for its time.
>>> Andrus
>>> On Apr 7, 2010, at 6:16 PM, Joe Baldwin wrote:
>>>> I am attempting to do more performance monitoring (with an eye towards optimizing
my design & use of DataObject lists and lifetime).
>>>> The first thing I would like to do is monitor how many DataObjects are created
and which JSP session they belong.
>>>> My idea was to simply create a constructor for the DataObject of interest
and place monitoring hooks inside. I would assume that I could also create a finalize method
to do similar things.
>>>> Is this the best way to create custom monitoring using Cayenne DataObjects
or is there a better way?
>>>> (BTW, even after reading the docs, I am still somewhat mystified by how my
configuration specifications control the life cycle and performance.  So I am hoping these
custom hooks will make my design decisions more visible, especially with multiple users.)
>>>> Thanks,
>>>> Joe

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