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From Michael Gentry <>
Subject Re: Cayenne object storage / memory usage
Date Sat, 10 Jun 2017 11:49:39 GMT
Hi John,

I'm a little surprised that map-based storage is over 2x worse in memory
consumption.  I'm wondering if there is more going on here than storage of
the property values.  Would it be simple enough to adapt your test case to
compare a list of POJOs vs a list of maps and see what the memory footprint
and difference is that way?

I personally was thinking the big improvement for using fields directly is
the speed improvement.  I didn't think the memory consumption difference
would be that dramatic.



On Fri, Jun 9, 2017 at 10:55 AM, John Huss <> wrote:

> I did some experimenting recently to see if changes to the way data in
> stored in Cayenne objects could reduce the amount of memory they consume.
> I chose to use separate fields for each property instead of a HashMap
> (which is what CayenneDataObject uses).  The results were very affirming.
> For my test of loading 10,000 objects from every table in my database I got
> it to use about about *half the memory* of the default class (from 921 MB
> down to 431 MB).
> I know there has been some discussion already about addressing this topic
> for the next major release, so I thought I'd throw in some observations /
> questions here.
> For my implementation I subclassed CayenneDataObject because in previous
> experience I found implementing a replacement to be much more difficult and
> subject to more bugs due to the less frequently used code path that
> PersistentObject and it's descriptors take you down.  My apps rely on
> things that are sort of specific to CayenneDataObject like Validating.
> So one question is how we should be addressing the need that people may
> have to create their own data classes. Right now I believe the recommended
> path is to subclass PersistentObject, but I'm not convinced that that is a
> viable solution without wholesale copying most of CayenneDataObject into
> your subclass.  I'd rather see a fuller base class (in addition to keeping
> PersistentObject around) that includes all of CayenneDataObject except the
> property storage (HashMap).
> For my implementation I had to modify CayenneDataObject, but only slightly
> to avoid creating the HashMap which I wasn't using. However, because class
> isn't really intended for customization this map is referenced in multiple
> methods that can't easily be overridden to change the way things are
> stored.
> Another approach might be to ask why anyone should need to customize the
> way data is stored in the objects if we can just use the best solution
> possible in the first place?  I can't imagine a more efficient
> representation that fields.  However, fields present difficulties for the
> use case where you aren't generating unique classes for your model but just
> rely on the generic class.  In theory this could be addressed via runtime
> code generation or something else, but that would be quite a change.
> So I'm looking forward to discussing this and toward the future.
> John

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