[BUG] Adding a large number of days to a date takes a very long time

[adamretter]

Initially, I believed that the following query appears to run forever, I also noticed that it pegs the CPU core running that thread at ~100% utilisation:

fn:current-date() + xs:dayTimeDuration("P1712073600000D")

In comparison:

• BaseX - returns an answer almost instantly.
• Saxon - returns an error instantly: E value is too large to be expressed in microseconds.

The root of the problem is not within eXist-db itself. eXist-db is simply relying on a 3rd-party implementation of the Java interface javax.xml.datatype.XMLGregorianCalendar. Various implementations are available, but eXist-db is using Xerces 2.12 for this.

---

As the JRE embeds a version of Xerces, we can actually just reproduce the problem in pure Java:

import javax.xml.datatype.DatatypeConfigurationException;
import javax.xml.datatype.DatatypeFactory;
import javax.xml.datatype.Duration;
import javax.xml.datatype.XMLGregorianCalendar;
import java.util.GregorianCalendar;

public class Main {

    public static void main(final String args[]) throws DatatypeConfigurationException {

        final DatatypeFactory factory = DatatypeFactory.newInstance();
        System.out.println("Using implementation from: " + factory.getClass().getPackageName());

        // get an XML calendar for `now`
        final GregorianCalendar nowCalendar = new GregorianCalendar();
        final XMLGregorianCalendar xmlCalendar = factory.newXMLGregorianCalendar(nowCalendar);

        // create a very large duration
        final Duration duration = factory.newDuration("P1712073600000D");

        // add the duration to the XML calendar
        xmlCalendar.add(duration);

        // print the new date from the XML calendar... do we ever get to this point?
        System.out.print(xmlCalendar);
    }
}

Tested on:

• Java 8 (1.8.0_382)
• Intel Xeon E5-1650 v3 @ 3.50GHz

Test command:

$ javac Main.java
$ java -cp . Main

Using implementation from: com.sun.org.apache.xerces.internal.jaxp.datatype
4687500329-08-10T18:24:56.192Z

6317.29s user 20.19s system 100% cpu 1:45:34.02 total

The above computation takes in excess of 1 Hour and 45 Minutes!

I believe that there must be room for optimising this, as BaseX is able to provide the result almost instantly...