How to improve xerces parser performance when large comments are present in xml file?

Question

I'm using the following code to parse an xml file using xerces 2.11:

@Test
public void testXercesPerformance() throws IOException, SAXException, ParserConfigurationException
{
    final SAXParserFactory spf = SAXParserFactory.newInstance();
    final SAXParser parser = spf.newSAXParser();
    final XMLReader xmlReader = parser.getXMLReader();
    final InputSource inputSource = new InputSource(new BufferedInputStream(new FileInputStream(new File("./some.xml")), 8192));
    xmlReader.parse(inputSource);
}

However the performance is very poor when the xml file just contains a few xml elements at the beginning and a large comment at the end (total file size about 10MB). In the course of parsing the parser successively allocates new Strings ending up at a total of 1.3TB of allocated strings (not all allocated at the same time). The parsing itself took 4 minutes to complete.

The file I used for testing started with:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.example</groupId>
    <version>1.0-SNAPSHOT</version>
    <artifactId>helloworld-secure</artifactId>
    <dependencies>
        <dependency>
            <groupId>org.eclipse.jetty</groupId>
            <artifactId>jetty-servlet</artifactId>
            <version>7.4.5.v20110725</version>
        </dependency>
        <dependency>
            <groupId>org.eclipse.jetty</groupId>
            <artifactId>jetty-security</artifactId>
            <version>7.4.5.v20110725</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>appassembler-maven-plugin</artifactId>
                <version>1.1.1</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals><goal>assemble</goal></goals>
                        <configuration>
                            <assembleDirectory>target</assembleDirectory>
                            <programs>
                                <program>
                                    <mainClass>HelloWorld</mainClass>
                                    <name>webapp</name>
                                </program>
                            </programs>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.3.2</version>
                <configuration>
            <source>1.6</source>
                    <target>1.6</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>
<!-- 
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.example</groupId>
    <version>1.0-SNAPSHOT</version>
    <artifactId>helloworld-secure</artifactId>
    <dependencies>

It then repeats the dependencies from the uncommented part hundreds of times until it reaches a size of nearly 10MB and ends with:

    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>appassembler-maven-plugin</artifactId>
                <version>1.1.1</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals><goal>assemble</goal></goals>
                        <configuration>
                            <assembleDirectory>target</assembleDirectory>
                            <programs>
                                <program>
                                    <mainClass>HelloWorld</mainClass>
                                    <name>webapp</name>
                                </program>
                            </programs>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.3.2</version>
                <configuration>
            <source>1.6</source>
                    <target>1.6</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>
-->

What's the cause of this poor performance and how should I configure the parser to improve performance?

Answer 1

The problem has been previously (well, more than 10 years ago) reported as XERCESJ-970. It has been fixed in revision 1507079 of xerces-j trunk since mid 2013.

The problem is a linearly growing buffer within XMLStringBuffer that too often needs to be reallocated.

The fix in my case was to rebuild xerces 2.11 with the patch from r1507079 applied.