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From "ant elder (JIRA)" <j...@apache.org>
Subject [jira] Commented: (ABDERA-267) Major performance issue with Abdera (underlying Axiom) object model while writing Atom DOM to XmlStreamWriter
Date Sat, 02 Oct 2010 08:10:32 GMT

    [ https://issues.apache.org/jira/browse/ABDERA-267?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12917169#action_12917169

ant elder commented on ABDERA-267:

Thanks for the detailed problem report Abhishek, this does sound like a useful update to do.

I had a try at updating Abdera to use axiom 1.2.9 and found there are a couple of non-backward
compatible API changes so we get three compile errors in the Abdera FOMDocument class all
related to constructor changes in axiom OMDocumentImpl. I don't suppose you would care to
have a go at tracking down the necessary code changes to getting Abdera to compile cleanly
with axiom 1.2.9 would you, and submitting a patch?

> Major performance issue with Abdera (underlying Axiom) object model while writing Atom
DOM to XmlStreamWriter
> -------------------------------------------------------------------------------------------------------------
>                 Key: ABDERA-267
>                 URL: https://issues.apache.org/jira/browse/ABDERA-267
>             Project: Abdera
>          Issue Type: Improvement
>    Affects Versions: 1.1
>         Environment: N/A
>            Reporter: Abhishek Shadangi
> *Background:*
> Abdera object model (OM) is based off of Axiom OM. In FOMDocument class (which extends
Axiom's OMDocumentImpl), method {{toWrite(java.io.Writer)}} makes a call to {{this.internalSerialize(javax.xml.stream.XmlStreamWriter)}}.
After this point Abdera delegate the XML stream writing to Axiom. 
> *Issue:*
> Axiom 1.2.7, has a serious performance issue if one is using likes of woodstox's implementation
(com.ctc.wstx.sw.SimpleNsStreamWriter - http://woodstox.codehaus.org/3.2.9/javadoc/index.html
), which I believe is the default writer used by Axiom.
> The {{internalSerialize}} call eventually makes it to {{org.apache.axiom.om.impl.util.OMSerializerUtil.serializeStartpart(OMElement
element, String localName, XMLStreamWriter writer)}}. Now, here starts the major performance
hog. This makes a call to {{isSetPrefixBeforeStartElement(XmlStreamWriter)}}, which handles
one of the MOST controversial part of the XmlStreamWriter spec - http://download.oracle.com/javase/6/docs/api/javax/xml/stream/XMLStreamWriter.html.
> They fairly recognized this in the javadocs for {{OMSerializerUtil.isSetPrefixBeforeStartElement}}
in Axiom version *1.2.7*. But they got the implementation all wrong. The implementation looks
for the property {{javax.xml.stream.XMLStreamWriter.isSetPrefixBeforeStartElement}} in the
writer, which throws an IllegalArgumentException if this property is not found, which IS NOT
FOUND. The implementation then catches this exception and returns false. This happens for
EVERY single element written to output stream. This exception handling is way too much expensive
and when it happens per element in XML per request, it takes MOST part of the processing time
every request. More on this specific property - http://publib.boulder.ibm.com/infocenter/realtime/v2r0/index.jsp?topic=/com.ibm.rt.doc.20/user/xml/xlxpj_reference.html.
> Since Abdera is meant for Atom feed, when there are concurrent requests the overall latency
per request increases more than linearly and after a while it becomes unusable for high load.
> Axiom realized this flaw in their logic and fixed it in *1.2.9*. Hence, Abdera SHOULD
consider upgrading it's code to use Axiom 1.2.9 instead of 1.2.7, and this performance issue
will be gone. For our use, I explicitly made this change to use the new Axiom library but
there are other dependencies which is preventing me to make the upgrade that easily.
> Most importantly, after upgrading the JAR, I get the following exception.:
>     Caused by: java.lang.IllegalStateException: This factory is immutable
> 	    at org.apache.axiom.util.stax.wrapper.ImmutableXMLOutputFactory.setProperty(ImmutableXMLOutputFactory.java:39)
> 	    at org.apache.abdera.parser.stax.StaxStreamWriter.createXMLStreamWriter(StaxStreamWriter.java:106)
> 	    at org.apache.abdera.parser.stax.StaxStreamWriter.setOutputStream(StaxStreamWriter.java:113)
> This is because javax.xml.stream.XmlOutputFactory and javax.xml.stream.XmlInputFactory,
that Axiom 1.2.9 creates, are now immutable and Abdera code is trying to set some {{javax.xml.stream.*}}
properties in them. To fix this, I updated StaxStreamWriter.createXMLStreamWriter and FOMParser.getXMLInputFactory
to NOT set any property. For our purposes this seems to work fine so far, but perhaps needs
a bit more research to make the real fix.
> *Action items:*
>  1. Upgrade to Axiom 1.2.9
>  2. Fix places where Abdera (esp. parser module) is trying to modify the immutable XmlInputFactory
and XmlOutputFactory as returned by Axiom.

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