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From Helder Magalhães <helder.magalh...@gmail.com>
Subject Re: Document insertion causing memory stress
Date Mon, 20 Apr 2009 10:55:12 GMT
Hi Alan,


> In an earlier thread I documented how my application merges one SVGElement
> into a main document.   It works, but when I do it multiple times my
> application slows down and crashes, most often with an "out of heap space"
> exception.  The SVG documents are not that complex (edited with inkscape).
>  The inserted document has about 6800 Nodes and no text elements.

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...


> In trying to figure out what is going on, I ran the Netbeans profiler to
> discover what objects are being created and by whom.  What I found was an
> astounding number of DOMMutationEvent objects (over 64,000) and also a huge
> number of HashMap$KeyIterator objects (over 27,000 using 890KB of memory),
> mostly created by
> SVGTextElementBridge$AttributedStringBuffer.toAttributedString();

Well, from a quick look it seems like there are good news and less
good (~=bad?) news. :-D

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).

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... ;-)


> I realize this is probably not enough detail to diagnose anything, but does
> this suggest anything to anyone about what I should be looking for or what I
> might be doing wrong?

Yeah, not much information to work with... :-|  Note that the source
of all this can be in the approach you have chosen to perform the
document merge itself -- there may be more than one way to accomplish
it...


Hope this helps,
 Helder


[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

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