Guys,
Comments below.
Markus Kohler wrote:
Hi Michael,
Thanks for the info.
Yes, there a ways to minimize the overhead and IMHO in practice a
naive implementation of this pattern has just too much overhead.
Yes, hash maps are just about the worst case of memory footprint you can
imagine, especially given that most implementations use instances of
Map.Entry to cause bloat in addition to the large index.
I know at least one real world example, where the memory usage of a
software component using this pattern could be reduced by a factor of
10.
The only potential upside of the naive pattern might be huge sparsely
populated instances. I.e., you have 1000 feature but only two or three
tend to be set on average.
People sometimes claim that memory is so cheap that this kind of
optimizations don't really matter.
Sometimes I make the silly claim that Java doesn't scale because
although my hardware has 4G I can't have a heap anywhere close to 2G in
size. The cheap memory claim is just silly.
I don't believe in this, just because if you use 10x more memory per
user, your scalability will most likely be limited by the memory usage.
Which basically means you will need more machines to serve the same
number of users, just because you didn't care that much about memory
usage.
It's just a stupid claim.
We had a discussion here about "bloat" lately and my understanding is,
that this topic is becoming more important because e4 will support a
multi user environment (please correct me if I'm wrong).
A lot of that talk was about bloat in the byte code and also about
static data that can never be garbage collected, but instance size is
quite important too.
I've been prototyping techniques for significantly reducing the size of
EObjectImpl. Perhaps by as much as 50% or more... In my opinion, ever
byte saved is a byte earned. :-P
In such a multi user environment the main concern is the amount of
memory you need per user, because as you increase the number of users
at some point in time the memory usage will be dominated by the
objects that are needed per user.
Therefore, if we talk about bloat I think that duplicated code might
not be the biggest problem, but rather duplicated data, especially
data duplicated per user.
I think they all add up. Often people are surprised by the byte code as
an issue because it's not an issue that scales, but rather is a
constant. I recall a case where folks changed their EMF generation
feature delegation pattern from the normal one to the less time
efficient Reflection delegation pattern. They also changed the
GenPackage's to use Initialize by Loading. They had *huge *models that
generally were used only during initialization. The reduction in byte
code resulted in a huge improvement in startup time and a huge reduction
in "retained memory", which the the performance loss for data access and
the increased memory footprint of the instances had no negative impact.
This was an excellent example of the opposite of what you might expect
and a great reminder that measurements speak louder than mental
exercises and abstract thinking..
IMHO the only approach that can avoid bloat is therefore to carefully
design which data can be shared between users and which data needs to
be there per user.
I think it would make sense to constantly monitor the memory usage
using automatic tests.
The Eclipse Memory Analyzer could be used for this kind of memory
usage tests.
I so totally agree. Measure, measure, measure again. Measure
everything. And when it comes to performance measurement, remember that
the observer often affects the observed and that unfortunately that
different JREs and different JIT implementations have a huge impact on
performance; often more than the optimizations you might be trying to
achieve with the changes you make.
Regards,
Markus
On Wed, Oct 22, 2008 at 8:34 AM, Michael Scharf
<[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>>
wrote:
Hi Markus,
> I once did some calculations for a simple Hashmap implementation
versus
> just using instance variables. See my old blog
> at http://www.sdn.sap.com/irj/sdn/weblogs?blog=/pub/wlg/5163
interesting post.
Yes, I thought both posts were interesting.
EMF is something in between.
Almost like a panacea. :-P
If you use
generated classes (fixed properties), the overhead is 4
additional object attributes.
A little worse than that, but I'm working on it in my copious spare time.
In case of dynamic EMF you
are much better than using HashMaps,
It's always much better than HashHaps, even for dynamic. And the
performance is better as well.
because the attributes
are stored in an array and the key (IStructuralFeature) has
an index into that array (I am sure Ed can give some
numbers here).
I think Eric confirmed that a EObject.eGet(feature) is twice as fast as
HashMap.get(key), and we even have InternalEObject.eGet(featureID) which
is faster yet...
So, with EMF you have the choice
between dynamic and fixed properties and you can
mix both approaches.....
In the sense you're using here, the set of properties is fixed; it's
just a case of are individual fields allocated per feature, or is an
array of slots allocated to hold all the features.
Unfortunately EMF is not good at delegating non existing
properties to another instance.
That's not quite true either. :-P
EMF supports the same type of thing as XML Schema's wildcards. So you
can have a property just like <xsd:any>. Other models (<schema>s) can
then declare global elements and those global elements (properties of
the document root of the corresponding EPackage) can be used as
properties on the object with the wildcard property.
Just two weeks ago I
worked with a colleague on an extension of EMF that
allows this (in fact it adds a kind of aspects (AOP) to
EMF that allows interception of the set/get methods).
>
http://steve-yegge.blogspot.com/2008/10/universal-design-pattern.html
Pretty interesting article but quite long -- I started reading
but after 30 min I decided to "fast read" the rest...
Yes, I'm not sure I agree with the overall outlook. Often people see
difference where I'll see commonalities. For example, I see little
significant difference between UML and XML Schema for the purpose of
this article. They're both modeling languages, each with a few features
the other doesn't have, but modeling languages nevertheless.
Michael
Hi all,
I agree that's an interesting post. But Steve IMHO doesn't
point out that the main problem with this approach is that it
can have a high memory overhead.
I once did some calculations for a simple Hashmap
implementation versus just using instance variables. See my
old blog at
http://www.sdn.sap.com/irj/sdn/weblogs?blog=/pub/wlg/5163
Regards,
Markus
On Mon, Oct 20, 2008 at 5:44 PM, Simon Kaegi
<[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
<mailto:[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>>> wrote:
http://steve-yegge.blogspot.com/2008/10/universal-design-pattern.html
_______________________________________________
eclipse-incubator-e4-dev mailing list
[email protected]
<mailto:[email protected]>
<mailto:[email protected]
<mailto:[email protected]>>
https://dev.eclipse.org/mailman/listinfo/eclipse-incubator-e4-dev
------------------------------------------------------------------------
_______________________________________________
eclipse-incubator-e4-dev mailing list
[email protected]
<mailto:[email protected]>
https://dev.eclipse.org/mailman/listinfo/eclipse-incubator-e4-dev
_______________________________________________
eclipse-incubator-e4-dev mailing list
[email protected]
<mailto:[email protected]>
https://dev.eclipse.org/mailman/listinfo/eclipse-incubator-e4-dev
------------------------------------------------------------------------
_______________________________________________
eclipse-incubator-e4-dev mailing list
[email protected]
https://dev.eclipse.org/mailman/listinfo/eclipse-incubator-e4-dev
_______________________________________________
eclipse-incubator-e4-dev mailing list
[email protected]
https://dev.eclipse.org/mailman/listinfo/eclipse-incubator-e4-dev
