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Subject [Cocoon Wiki] New: ProfilingPipelinesWithBigSaxEventStreams
Date Fri, 25 Feb 2005 15:17:41 GMT
   Date: 2005-02-25T07:17:41
   Editor: NicoVerwer
   Wiki: Cocoon Wiki
   Page: ProfilingPipelinesWithBigSaxEventStreams

   no comment

New Page:

= Profiling pipelines with big SAX-event streams =

The profiliing pipelines, `ProfilingCachingProcessingPipeline` and `ProfilingNonCachingProcessingPipeline`
are useful to measure the performance of your Cocoon application.
However, when the XML that you process is really big (millions of SAX events), these pipelines
crash sometimes with an error like:

org.apache.cocoon.ProcessingException: Failed to execute pipeline.: org.xml.sax.SAXException:
Index too large

This error is caused by the `XMLByteStreamCompiler`, which is used to store a compiled format
of the SAX-event stream in a byte-array (I am not sure why that is needed).
Especially when you are dealing with large documents, measuring performance can be very important,
but if the profiling pipelines give up, some other method must be used.

'''Warning: In the rest of this page, some ugly coding techniques are used.
Do not use the code given here as an example of how to program Cocoon components.'''

Instead of one of the profiling pipelines, a normal (non-profiling, and probably non-caching)
pipeline must be used. The performance measuring is done by a new transformer, the `LOWProfilerTransformer`
(see the attachment).
'LOWProfiler' means 'Log-file Output Writing Profiler', and also indicates that the standard
profiler is preferable.
The `LOWProfilerTransformer` must be inserted in the pipeline, just before the serializer,

      <map:match pattern="test">
        <map:generate src="bigfile.xml"/> some transformations etc...
        <map:transform type="lowprofiler"/>
        <map:serialize type="xml"/>

You will need to declare the transformer:

    <map:transformers default="xslt">
      <map:transformer name="lowprofiler"

As you can see, a new log-file is needed where the profiling results are written. This is
declared in `logkit.xconf`:

    <cocoon id="lowprofiler">
      <format type="cocoon">
        %7.7{priority} %{time}   [%{category}] (%{uri}) %{thread}/%{class:short}: %{message}\n
    <category log-level="INFO" name="lowprofiler">
        <log-target id-ref="lowprofiler"/>

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