XML schema creation takes long time

Question

I have the following code:

public XsdValidator(Resource... xsds) {
    Preconditions.checkArgument(xsds != null);
    try {
      this.xsds = ImmutableList.copyOf(xsds);
      SchemaFactory schemaFactory = SchemaFactory.newInstance(W3C_XML_SCHEMA_NS_URI);
      LOGGER.debug("Schema factory created: {}",schemaFactory);
      StreamSource[] streamSources = streamSourcesOf(xsds);
      LOGGER.debug("StreamSource[] created: {}",streamSources);
      Schema schema = schemaFactory.newSchema(streamSources);
      LOGGER.debug("Schema created: {}",schema);
      validator = schema.newValidator();
      LOGGER.debug("Validator created: {}",validator);
    } catch ( Exception e ) {
      throw new IllegalArgumentException("Can't build XsdValidator",e);
    }
  }

It seems the line schemaFactory.newSchema(streamSources); takes a very long time (30 seconds) to execute against my XSD file.

After many tests on this XSD, it seems it's because I have:

  <xs:complexType name="entriesType">
    <xs:sequence>
      <xs:element type="prov:entryType" name="entry" minOccurs="0" maxOccurs="10000" />
    </xs:sequence>
  </xs:complexType>

The problem is maxOccurs="10000"

With maxOccurs="1" or maxOccurs="unbounded" , it is very fast.

Can someone tell me what's the problem of using maxOccurs="10000" ?

Answer 1

Based on my personal experience, having particles bounded by what some may consider "unreasonably" high values is cause for performance problems ( this link is from my browser's favourites).

The underlying cause seems to be memory allocation (to the effect indicated by the maxOccurs value).

Also, I recall a documentation item which was stating a threshold value beyond which, for all intents and purposes, the parser would actually treat the maxOccurs as unbounded, regardless of what the XSD says (I'll revisit this post if I find it).