Why is Intel XSLT accelerator so slow ?

[killy971]

I have been testing different libraries to process XSL transformations
on large XML files.

The fact is that I read a document from Intel, stating their library
(XSLT accelerator) was more twice faster than Apache Xalan, and was
designed to perform well on large XML files.
- http://isdlibrary.intel-dispatch.com/isd/10/wp_XSLT.PDF
- http://www.intel.com/cd/software/products/asmo-na/eng/366637.htm
Please note that their benchmark was only performed with small XML
files, under 200 ko.

I downloaded their evaluation version, configured it to work with 2
threads.
My computer specs are "dual core Intel processor (2.40GHZ), with 2GB
of ram".

I made tests on XML files that consists of a simple header and footer,
and the content is a sequence of the following piece of XML :

<log>
<timestamp>2008-01-02 00:00:08</timestamp>
<host name="mail-server">122.122.122.122</host>
<pid/>
<facility>mail</facility>
<priority>notice</priority>
<message> The key values: Key1=A, Key2=C, Key3=E and Key4=G.
000008351</message>
<application name="Benchmark">
<action name="misc" color="FFFFFF">
<param tag="key1" name="Key1">A</param>
<param tag="key2" name="Key2">C</param>
<param tag="key3" name="Key3">E</param>
<param tag="key4" name="Key4">G</param>
</action>
</application>
</log>

By repeating this pattern, I made test files with different file
sizes, from 1MB to 200MB, and tested the XSL transformation process
(with an XSL file transforming the XML file to an HTML file) with the
two libraries.

For little XML files (under 4MB), Intel XSLT accelerator performances
were better than Xalan performances, but for bigger files, XSLT
accelerator starts to be _very_ slow (exponential growth of the
processing time).

An extract of the result of my benchmark :

10MB XML file
- Xalan : 4.5 seconds (processing time)
- XSLT accelerator : 19.4 seconds

30MB XML file
- Xalan : 11.4 seconds
- XSLT accelerator : 191.2 seconds

50MB XML file
- Xalan : 18.4 seconds
- XSLT accelerator : 548.4 seconds (~30 times slower !)

Concerning Intel library, the only configurations options were the
working thread number, and the memory allocated to the process. I
tried different settings, but always obtained the same results (and
the best results were for 2 working threads).

I contacted Intel support, but didn't get any explanation on this
problem.

I would like to know if anyone has already experienced the same
problem, and if there is a way to get Intel XSLT accelerator to
outperform Xalan performances on large XML file processing (or at
least to get the same performances).

Has anyone ever used Intel XSLT accelerator for large XML file
processing ?

In the end, does anyone know a library that really outperform Xalan
performances on XSL transformations, especially concerning the
OutOfMemoryError ?
(with my XML format and XSL sheet, this error occurs when the memory
allocated to the JVM is less than about 3.4 times the size of the XML
file I try to process)

(The reason I am interested in Intel library is that it doesn't seem
to crash even when processing large xml files. Xalan does, when the
memory allocated to the JVM is not enough)

 

[Juergen Kahrs]

By repeating this pattern, I made test files with different file
sizes, from 1MB to 200MB, and tested the XSL transformation process
(with an XSL file transforming the XML file to an HTML file) with the
two libraries.

Interesting, be aware that file sizes of 200 MB are
usually too large to be processes with XSLT. It will
work in principle, but should be done offline because
it simply takes too long for interactive use.

For little XML files (under 4MB), Intel XSLT accelerator performances
were better than Xalan performances, but for bigger files, XSLT
accelerator starts to be _very_ slow (exponential growth of the
processing time).

An extract of the result of my benchmark :

10MB XML file
- Xalan : 4.5 seconds (processing time)
- XSLT accelerator : 19.4 seconds

30MB XML file
- Xalan : 11.4 seconds
- XSLT accelerator : 191.2 seconds

50MB XML file
- Xalan : 18.4 seconds
- XSLT accelerator : 548.4 seconds (~30 times slower !)

Congratulations for your systematic analysis.
You have already found the problem:

Xalan run-time increases as O(n), this means roughly 5-fold run-time for 5-fold size.
XSLT accelerator run-time increases as O(n^2), this means roughly 25-fold run-time for 5-fold size.


This problem wont be solved by "optimization" in the usual sense.
The algorithm has to be changed.

 

[Joseph J. Kesselman]

For little XML files (under 4MB), Intel XSLT accelerator performances
Very different codebases. Probably different tradeoffs taken at all
levels from data structures to algorithms. I'm not surprised that the
performance curves cross each other.

Reminder; XSLT, in general, requires that the whole input document be
loaded into an in-memory data model since the stylesheet has full random
access to it. Efficiency of that model becomes a serious issue on large
docs, since swapping can be a performance-killer.

See much discussion on Xylem's mailing list archives of what we've done
over the years (including some "cheats" for some specific usecases), and
what we've considered as possible future directions if cycles ever
become available to invest in that work.