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From Alan Deikman <Alan.Deik...@znyx.com>
Subject Re: Document insertion causing memory stress
Date Mon, 20 Apr 2009 18:38:46 GMT
Helder Magalhães wrote:
> Well, for the heap space issue, you should really consider increasing
> the memory limit allocated to the JVM (the default is not even enough
> for medium complexity graphics, "medium" being naturally a very
> subjective measurement). ;-)  Lots of threads on this subject on the
> mailing list (and even a few in the bug tracker) -- guess a FAQ [1]
> item for this would made sense, even if this is not related with
> Batik, as it's a common Java misconception...
Well I did end up increasing the memory available to the JVM -- probably 
later than I should have.   That's where the "subjective" you mentioned 
comes in -- I wasn't prepared to accept the amount of memory my 
application would take.  The fully assembled graphic to me is not really 
complex (one parent graphic, and about 16 grafted-in graphics) but the 
Batik-related objects (as far as I can tell from the Netbeans profiler) 
are taking up about 120MB to render it -- and that's after GC.

If I were doing this all with Swing natively it would be much harder to 
program to get the same feature set but it would take about 1/10th the 
memory.  At least the result with Batik looks great and performs well.  
That's a win.

At least I know now that my program logic is correct -- and that I am 
not up against some sort of Batik "bug" that I am ill-prepared to figure 

> The good news is that all of this should be expected. :-)  As you said
> to be merging a document into another one, then the main document's
> DOM will be updated: that explains the high number of
> "DOMMutationEvent" objects. As we're at it, you may consider taking a
> look at this rather interesting and powerful mechanism [2] [3]. ;-)
> I'd say that the "HashMap$KeyIterator" objects correspond to pointers
> to elements and element attributes of the document being merged. The
> high number of both of these objects are likely coherent with the
> almost 7000 nodes you said the document being merged contained
> (probably is the sum of element attributes and maybe of elements
> also).
This does seem to be the case.  However I suspect that many of the 
HashMaps floating around also have something to do with the GC process 
-- a byproduct of instantiating and throwing away a lot of objects.  I 
just don't know enough about it to be sure.

> The less good news is that I'm not sure how to workaround this. I'm
> fairly convinced that you can (temporarily) disable the DOM Mutation
> events from being triggered (crawling through the examples and
> documentation might help) or, if you don't need them, maybe completely
> disable this functionality (note that I'm also not sure if this would
> break Batik internally!). Disabling the DOM Mutation events should
> lead to a temporary performance improvement and memory decrease while
> doing the merge. As for the "HashMap$KeyIterator", I don't think you
> can do much about it, but that's also far beyond my knowledge of
> Batik... ;-)
This solution did occur to me -- what would be called for is an 
optimized importNode method that avoids this problem.  What might also 
work better is to just build an SVGDocument from scratch each time and 
invoking a Builder (I don't think DOM mutations occur in that process).

 From this experience what I would ask the Batik developers for is some 
way of monitoring and controlling memory usage.  It is easy enough to 
get an object count given a Node parameter, but what is really needed is 
a way to get the concrete implementation to fess up on what objects it 
has instantiated and what memory they use.

When I have some time I am going to look deeper into this.   For now 
since I am up and running (memory is cheap, right?) I have to set this 
aside and focus on my business logic. 

> Hope this helps,
>  Helder
You always seem to have a useful link or two.   Thanks for the pointers.

> [1] http://xmlgraphics.apache.org/batik/faq.html
> [2] http://www.xml.com/pub/a/2002/10/09/mutate.html
> [3] http://www.w3.org/TR/DOM-Level-2-Events/events.html#Events-eventgroupings-mutationevents
Alan Deikman

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