As it happens the limit on the number of namespace prefixes has gone in the 9.4 development branch, though there's still a limit of 32K namespace URIs and a limit of 1K prefixes per URI.

It would be nice to have limits that are sufficiently high that no-one will ever reach them, but I'm afraid I've decided several times over the years that redesigning the name pool for the benefit of this one rogue application really can't be justified.

I vaguely recall writing an XMLFilter on one occasion to normalize the namespace prefixes, but I can't lay my hands on it now.

Using a static TransformerFactory itself seems a poor design choice.

Sorry for the inconvenience!

Michael Kay

On 09/08/2011 05:11, Scott Robey wrote:
Thanks for the quick response, Michael.

From what I can tell looking at the NamePool source, there is a minor logic error that prevents it from failing nicely. Specifically, because the prefixes array is set to double the prefixesUsed number, each time it's exceeded, the following conditional may not be met:

 if (prefixesUsed >= prefixes.length) {
            if (prefixesUsed > 32000) {
                throw new NamePoolLimitException("Too many namespace prefixes");

The array will be doubled to something like 393216, and the prefixesUsed will exceed the max size for short before the above test fails...I think. Anyway, that's not really a big deal.

You are correct about the pathological Apache application, our clients are using an old version of Axis2 (1.2) and it appears to be creating a new namespace prefix for every web service request, so eventually I get prefixes that look like: axis2ns32001, hence the exception once the client has sent requests with more than 32767 different namespaces. Until the clients upgrade to a newer version of Axis2, however,  I'm kind of stuck and need to find a workaround.

I understand your reasoning that the application should not be using such a vast number of namepsace prefixes, but you can't always control what your clients are sending, right? There could be thousands of different clients using different data-binding tools and thus possibly using many different prefixes, seems like sooner or later your application will exceed the limitations imposed by the NamePool design. I'm not speaking from actual practical experience though, more theoretical, so maybe in the real world this isn't really an issue and the tools tend to reuse namespace prefixes (ns1, ns2, etc.).

In any case, in my situation, I don't have control over the lifecycle of the TransformerFactory, so I can't create multiple Saxon instances to handle the workload. This is because the JAXB RI is using a static TransformerFactory, see com.sun.xml.bind.v2.runtime.JAXBContextImpl. It's out of my control.

I'm going to pursue a workaround on the client side, such that the web service requests don't contain an infinite number of different prefixes, I think I can do this using a different Axis2 API.

Thanks for your time.

-Scott Robey

From: Michael Kay <>
Sent: Monday, August 8, 2011 3:52 AM
Subject: Re: [saxon] Saxon HE ArrayIndexOutOfBoundsException: -32768 in NamePool.allocateCodeForPrefix(

Yes, this is a known limit. I thought that these days it would fail cleanly saying the limit had been exceeded, but it seems that's not the case on this path.

There's a pathological Apache application - I've forgotten which - that generates XML in which a new namespace prefix is allocated (for the same namespace URI) on every element instance. The Saxon NamePool can't handle that. I don't know if that's the situation here. (In fact, I think that example would hit a different limit, namely a maximum of 1024 prefixes per namespace URI).

Devising a workaround involves understanding why the application is using such a vast number of different namespace prefixes. Is it generating prefixes at random for a small and stable set of namespace URIs? If that's the case, then one could insert a SAX filter to normalize the prefixes (assuming they don't also appear in content). On the other hand, if the number of namespace URIs is also very large, then one might have to look at ways of using multiple Saxon instances to handle the workload.

Michael Kay

On 07/08/2011 21:55, Scott Robey wrote:
I have an application using Saxon HE ( and JAX-WS/JAXB. During stress testing, after the application has processed several thousand XML messages, the following exception gets thrown repeatedly, and the application becomes unable to process XML until the JVM is cycled.

java.lang.ArrayIndexOutOfBoundsException: -32768
    at net.sf.saxon.event.ReceivingContentHandler.getNameCode(
    at net.sf.saxon.event.ReceivingContentHandler.startElement(

I've looked at the NamePool source, and it appears that the NamePool object referenced by the Configuration object has a limitation of only being able to handle ~32000 different namespace prefixes throughout the life of the application. My question is: is this a known and accepted limitation of the Saxon XSLT processor? Is there any way I can work around the issue given that JAXB is creating the TransformerFactory, and I have no control over its lifecycle?

The following JUnit test demonstrates the problem. The test case fails consistently when using the Saxon processor, and the test case passes reliably when using the standard JDK's TransformerFactory.

  public void testArrayIndexOutOfBoundsException() throws Exception {
    final long MAX = 33000;
    final String XML_TEMPLATE = "<ns%1$s:element xmlns:ns%1$s=\"urn:ns1\">test</ns%1$s:element>";
    TransformerFactory factory = TransformerFactory.newInstance();
    System.out.println("TransformerFactory: " + factory);
    for ( long i = 0; i < MAX; i++ ) {
      String xml = String.format(XML_TEMPLATE,  i);
      DOMResult result = new DOMResult();
      try {
          new StreamSource(new ByteArrayInputStream(xml.getBytes())), result);
      catch ( Exception e ) {
        e.printStackTrace();"After: " + i + " iterations. " + e);

Any insight is appreciated.


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