On May 8, 2008, at 11:38, Jean-François El Fouly wrote:
Andreas Delmelle a écrit :
Which Java VM are you using? Practically every time someone tells
us about memory/GC issues, it appears they are using an
implementation other than Sun (IBM, GNU...)
Up to now, we still have to find out why precisely non-Sun VMs
have difficulties with FOP...
Nope. I'll double check but I'm pretty sure it's a genuine Sun JVM
1.5.0_11, or maybe the very minor build after.
OK. Just curious: Any chance you could test it on another build or
maybe even Java 6?
How large would the resulting FO-files be if you dump them to the
filesystem? The XML by itself says very little. From a 1.5MB XML,
you could get a FO of a few KB or one of 26MB, depending on the
stylesheet.
5.08 Mb.
That's not what I would call a large FO, so this should be no problem.
Does the stylesheet adhere to XSLT best practices? Does it
generate a lot of redundant fo:blocks, fo:inlines?
I hope not. It has been a complicated thing generated by
StyleVision in the very beginning but it has been simplified and
tweaked a lot.
In my personal experience, optimizing the stylesheet code usually
does not offer much improvement in terms of global memory usage, but
it could have a noticeable impact on the processing time. One of the
things I've learned about generated XSL-FO stylesheets by Altova is
that they add a lot of fo:inlines to specify, for example, font-
properties on the lowest levels in the generated FO while, when
comparing to the font-properties of the fo:inlines' parents nothing
really changes, except for the size, style or weight. From FOP's
point of view, that's somewhat of a waste. Much better to specify a
global font-size on the page-sequence, and override on the lower
levels only what is really necessary. After adapting the stylesheet
manually, and removing the redundant fo:inlines, the stylesheet and
the generated FO were reduced to not even half the original size.
Something else that bothered me, but I don't know if that was also
generated by Altova, is that in one of the stylesheets I saw, the
entire transformation was contained in one giant template... AFAIU,
this gives little opportunity for the XSLT processor to clean up
anything. Java 1.5 uses Xalan XSLTC by default, which converts
templates into Java objects. One giant template would then mean one
very long-living object that may reference numerous others for the
whole duration of the processing run. If you look at the chain, when
using XML+XSLT input, FOP is always the first one to finish, then the
XSLT processor, then the XML parser.
If the XSLT processor cannot reclaim anything, this will give FOP
less room to work with, so it ultimately runs slower. As the heap
increases to reach the maximum, the points where the JVM will launch
the GC by itself, will also increase. Since it cannot expand the heap
anymore, it will try to clean up more frequently.
Cheers
Andreas
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