One way to get the best of both worlds (scalability of a streaming parser, but convenience of DOM) is to use DOM4J's ElementHandler interface[1].  You parse the XML file using a SAXReader, and register a class to handle callbacks, based on an XPath expression.  I used this approach to break up giant MARCXML files with hundreds of thousands of records.

Though this approach does require the XML to be well-formed.  I had some problems with that, and wound up pre-processing the MARCXML to strip out illegal characters so they wouldn't cause parsing errors.


1. http://dom4j.sourceforge.net/dom4j-1.6.1/apidocs/org/dom4j/ElementHandler.html


-Esme
--
Esme Cowles <[log in to unmask]>

"The wages of sin is death but so is the salary of virtue, and at least the
 evil get to go home early on Fridays." -- Terry Pratchett, Witches Abroad

On 06/8/2012, at 2:36 PM, Kyle Banerjee wrote:

> I'm working on a script that needs to be able to crosswalk at least a
> couple hundred XML files regularly, some of which are quite large.
> 
> I've thought of a number of ways to go about this, but I wanted to bounce
> this off the list since I'm sure people here deal with this problem all the
> time. My goal is to make something that's easy to read/maintain without
> pegging the CPU and consuming too much memory.
> 
> The performance and load I'm seeing from running the files through LibXML
> and SimpleXML on the large files is completely unacceptable. SAX is not out
> of the question, but I'm trying to avoid it if possible to keep the code
> more compact and easier to read.
> 
> I'm tempted to streamedit out all line breaks since they occur in
> unpredictable places and put new ones at the end of each record into a temp
> file. Then I can read the temp file one line at a time and process using
> SimpleXML. That way, there's no need to load giant files into memory,
> create huge arrays, etc and the code would be easy enough for a 6th grader
> to follow. My proposed method doesn't sound very efficient to me, but it
> should consume predictable resources which don't increase with file size.
> 
> How do you guys deal with large XML files? Thanks,
> 
> kyle
> 
> <rant>Why the heck does the XML spec require a root element,
> particularly since large files usually consist of a large number of
> records/documents? This makes it absolutely impossible to process a file of
> any size without resorting to SAX or string parsing -- which takes away
> many of the advantages you'd normally have with an XML structure. </rant>
> 
> -- 
> ----------------------------------------------------------
> Kyle Banerjee
> Digital Services Program Manager
> Orbis Cascade Alliance
> <[log in to unmask]>[log in to unmask] / 503.999.9787