<?xml version="1.0" encoding="UTF-8"?>
<!-- $Id: scheduler.xml 17299 2012-10-10 23:47:33Z joewiz $ --><book><bookinfo><productname>eXist-db – Open Source Native XML Database</productname><title>Scheduler Module</title><date>September 2009</date><author><firstname>Loren</firstname><surname>Cahlander</surname><affiliation><address format="linespecific"><email>loren at syntactica.com</email></address></affiliation></author></bookinfo><chapter><title>Scheduler Module</title><section><title>Introduction</title><para>Quartz is a full-featured, open source job scheduling system that has been
                integrated with eXist. Quartz can be used to create simple or complex schedules for
                executing tens, hundreds, or even tens-of-thousands of jobs. The Quartz Scheduler
                includes many enterprise-class features, such as JTA transactions and
                clustering.</para><section><title>Activating</title><para> There are two type of uses of the Quartz Scheduler within eXist-db. The first
                    is always active and is invoked at system startup. The second is the XQuery
                    function module for initiating and managing scheduled jobs. This second use is
                    not activated <emphasis role="italic">out-of-the-box</emphasis>. It has to be
                    activated through the conf.xml file. </para><section><title>System Startup</title><para>The jobs that are initiated at system startup are invoked by the settings
                        within the &lt;scheduler&gt; tag in the <emphasis role="bold">conf.xml</emphasis> file. There is a full set of instructions with
                        example jobs (that are commented out) in the file.</para></section><section><title>XQuery Function Module</title><para>The scheduler XQuery function module is activated by uncommenting the
                        following in conf.xml:</para><example><title>Scheduler XQuery Module in conf.xml</title><programlisting language="xml">&lt;module class="org.exist.xquery.modules.scheduler.SchedulerModule" 
           uri="http://exist-db.org/xquery/scheduler" /&gt;</programlisting></example><para>Once the scheduler XQuery function module is active, then XQuery code can
                        be written to invoke and manage <emphasis role="bold">user</emphasis> type
                        jobs.</para></section></section><section><title>Type</title><para>The type of the job to schedule. Must be either "startup", "system" or
                    "user".</para><variablelist><varlistentry><term>startup</term><listitem><para>Startup jobs are executed once during the database startup but
                                before the database becomes available, these jobs are
                                synchronous.</para></listitem></varlistentry><varlistentry><term>system</term><listitem><para>System jobs require the database to be in a consistent state. All
                                database operations will be stopped until the method returns or
                                throws an exception. Any exception will be caught and a warning
                                written to the log.</para></listitem></varlistentry><varlistentry><term>user</term><listitem><para>User jobs may be scheduled at any time and may be mutually
                                exclusive or non-exclusive</para></listitem></varlistentry></variablelist></section></section><section><title>Java vs. XQuery Jobs</title><section><title>Introduction</title><para>There are two types of jobs that can be scheduled. They are Java and XQuery.
                    Java jobs can be startup, system or user. XQuery jobs can only be user
                    jobs.</para></section><section><title>XQuery Jobs</title><para> If the job is written in XQuery (not suitable for startup or system jobs)
                    then this should be a path to an XQuery stored in the database. e.g. <emphasis role="bold">/db/myCollection/myJob.xql</emphasis></para><para>XQuery job's will be launched under the guest account initially, although the
                    running XQuery may switch permissions through calls to <emphasis role="bold">xmldb:login()</emphasis>. </para></section><section><title>Java Jobs</title><para>A Java job that is to be invoked from the XQuery function module has to be
                    extended from the <emphasis role="bold">org.exist.scheduler.UserJavaJob</emphasis> class. A startup or system Java
                    job that is invoked from the conf.xml file implements <emphasis role="bold">org.exist.storage.SystemTask</emphasis>.</para><example><title>Sample Java Source File</title><programlisting format="linespecific" language="java">
package org.exist.scheduler;

import java.util.Map;

import org.exist.storage.BrokerPool;

public class TestJob extends UserJavaJob {

    private String jobName = this.getClass().getName();
    
	public void execute(BrokerPool brokerpool, Map params) throws JobException {
		
		System.out.println("****** TEST JOB EXECUTED ******");

	}

	public String getName() {
		return jobName;
	}

    public void setName(String name) {
        this.jobName = name;
    }
}</programlisting></example></section></section><section><title>Periodic</title><section><title>Introduction</title><para>A scheduled job can be run on a periodic basis. When the job is scheduled, it
                    can be specified to run every <emphasis role="italic">n</emphasis> milliseconds.
                    There is the additional option to start after <emphasis role="italic">x</emphasis> milliseconds and to only be repeated <emphasis role="italic">y</emphasis> times after the initial execution.</para></section></section><section><title>Cron</title><note><para>This section was copied from <ulink url="http://www.opensymphony.com/quartz/wikidocs/CronTriggers%20Tutorial.html" condition="_blank">OpenSymphony CronTriggers Tutorial</ulink>.</para></note><section><title>Introduction</title><para>cron is a UNIX tool that has been around for a long time, so its scheduling
                    capabilities are powerful and proven. The CronTrigger class is based on the
                    scheduling capabilities of cron. </para><para>CronTrigger uses "cron expressions", which are able to create firing schedules
                    such as: "At 8:00am every Monday through Friday" or "At 1:30am every last Friday
                    of the month". </para><para>Cron expressions are powerful, but can be pretty confusing. This tutorial aims
                    to take some of the mystery out of creating a cron expression, giving users a
                    resource which they can visit before having to ask in a forum or mailing list.
                </para></section><section><title>Format</title><para>A cron expression is a string comprised of 6 or 7 fields separated by white
                    space. Fields can contain any of the allowed values, along with various
                    combinations of the allowed special characters for that field. The fields are as
                    follows: </para><table border="1"><caption>Fields</caption><colgroup><col width="25%"/><col width="25%"/><col width="30%"/><col width="20%"/></colgroup><tbody><tr><th>Field Name</th><th>Mandatory?</th><th>Allowed Values</th><th>Allowed Special Characters</th></tr><tr><td>Seconds</td><td>YES</td><td>0-59</td><td>, - * /</td></tr><tr><td>Minutes</td><td>YES</td><td>0-59</td><td>, - * /</td></tr><tr><td>Hours</td><td>YES</td><td>0-23</td><td>, - * /</td></tr><tr><td>Day of month</td><td>YES</td><td>1-31</td><td>, - * ? / L W</td></tr><tr><td>Month</td><td>YES</td><td>1-12 or JAN-DEC</td><td>, - * /</td></tr><tr><td>Day of week</td><td>YES</td><td>1-7 or SUN-SAT</td><td>, - * ? / L #</td></tr><tr><td>Year</td><td>NO</td><td>empty, 1970-2099</td><td>, - * /</td></tr></tbody></table><para>So cron expressions can be as simple as this: * * * * ? * </para><para>or more complex, like this: 0 0/5 14,18,3-39,52 ? JAN,MAR,SEP MON-FRI
                    2002-2010 </para></section><section><title>Special characters</title><itemizedlist><listitem><para> * ("all values") - used to select all values within a field. For
                            example, "*" in the minute field means "every minute". </para></listitem><listitem><para> ? ("no specific value") - useful when you need to specify something
                            in one of the two fields in which the character is allowed, but not the
                            other. For example, if I want my trigger to fire on a particular day of
                            the month (say, the 10th), but don't care what day of the week that
                            happens to be, I would put "10" in the day-of-month field, and "?" in
                            the day-of-week field. See the examples below for clarification. </para></listitem><listitem><para> - - used to specify ranges. For example, "10-12" in the hour field
                            means "the hours 10, 11 and 12". </para></listitem><listitem><para> , - used to specify additional values. For example, "MON,WED,FRI" in
                            the day-of-week field means "the days Monday, Wednesday, and Friday".
                        </para></listitem><listitem><para> / - used to specify increments. For example, "0/15" in the seconds
                            field means "the seconds 0, 15, 30, and 45". And "5/15" in the seconds
                            field means "the seconds 5, 20, 35, and 50". You can also specify '/'
                            after the '' character - in this case '' is equivalent to having '0'
                            before the '/'. '1/3' in the day-of-month field means "fire every 3 days
                            starting on the first day of the month". </para></listitem><listitem><para> L ("last") - has different meaning in each of the two fields in which
                            it is allowed. For example, the value "L" in the day-of-month field
                            means "the last day of the month" - day 31 for January, day 28 for
                            February on non-leap years. If used in the day-of-week field by itself,
                            it simply means "7" or "SAT". But if used in the day-of-week field after
                            another value, it means "the last xxx day of the month" - for example
                            "6L" means "the last friday of the month". When using the 'L' option, it
                            is important not to specify lists, or ranges of values, as you'll get
                            confusing results. </para></listitem><listitem><para> W ("weekday") - used to specify the weekday (Monday-Friday) nearest
                            the given day. As an example, if you were to specify "15W" as the value
                            for the day-of-month field, the meaning is: "the nearest weekday to the
                            15th of the month". So if the 15th is a Saturday, the trigger will fire
                            on Friday the 14th. If the 15th is a Sunday, the trigger will fire on
                            Monday the 16th. If the 15th is a Tuesday, then it will fire on Tuesday
                            the 15th. However if you specify "1W" as the value for day-of-month, and
                            the 1st is a Saturday, the trigger will fire on Monday the 3rd, as it
                            will not 'jump' over the boundary of a month's days. The 'W' character
                            can only be specified when the day-of-month is a single day, not a range
                            or list of days. The 'L' and 'W' characters can also be combined in the
                            day-of-month field to yield 'LW', which translates to "last weekday of
                            the month". </para></listitem><listitem><para> # - used to specify "the nth" XXX day of the month. For example, the
                            value of "6#3" in the day-of-week field means "the third Friday of the
                            month" (day 6 = Friday and "#3" = the 3rd one in the month). Other
                            examples: "2#1" = the first Monday of the month and "4#5" = the fifth
                            Wednesday of the month. Note that if you specify "#5" and there is not 5
                            of the given day-of-week in the month, then no firing will occur that
                            month. The legal characters and the names of months and days of the week
                            are not case sensitive. MON is the same as mon. </para></listitem></itemizedlist></section><section><title>Examples</title><para>Here are some full examples:</para><table border="1"><caption>Examples</caption><colgroup><col width="30%"/><col width="70%"/></colgroup><tbody><tr><th>Expression</th><th>Meaning</th></tr><tr><td>0 0 12 * * ? </td><td> Fire at 12pm (noon) every day </td></tr><tr><td>0 15 10 * * ?</td><td>Fire at 10:15am every day</td></tr><tr><td>0 15 10 * * ? *</td><td>Fire at 10:15am every day</td></tr><tr><td>0 15 10 * * ? 2005</td><td>Fire at 10:15am every day during the year 2005</td></tr><tr><td>0 * 14 * * ?</td><td>Fire every minute starting at 2pm and ending at 2:59pm, every
                                day</td></tr><tr><td>0 0/5 14 * * ?</td><td>Fire every 5 minutes starting at 2pm and ending at 2:55pm, every
                                day</td></tr><tr><td>0 0/5 14,18 * * ?</td><td>Fire every 5 minutes starting at 2pm and ending at 2:55pm, AND fire
                                every 5 minutes starting at 6pm and ending at 6:55pm, every day</td></tr><tr><td>0 0-5 14 * * ?</td><td>Fire every minute starting at 2pm and ending at 2:05pm, every
                                day</td></tr><tr><td>0 10,44 14 ? 3 WED</td><td>Fire at 2:10pm and at 2:44pm every Wednesday in the month of
                                March.</td></tr><tr><td>0 15 10 ? * MON-FRI</td><td>Fire at 10:15am every Monday, Tuesday, Wednesday, Thursday and
                                Friday</td></tr><tr><td>0 15 10 15 * ?</td><td>Fire at 10:15am on the 15th day of every month</td></tr><tr><td>0 15 10 L * ?</td><td>Fire at 10:15am on the last day of every month</td></tr><tr><td>0 15 10 ? * 6L</td><td>Fire at 10:15am on the last Friday of every month</td></tr><tr><td>0 15 10 ? * 6L</td><td>Fire at 10:15am on the last Friday of every month</td></tr><tr><td>0 15 10 ? * 6L 2002-2005</td><td>Fire at 10:15am on every last friday of every month during the years
                                2002, 2003, 2004 and 2005</td></tr><tr><td>0 15 10 ? * 6#3</td><td>Fire at 10:15am on the third Friday of every month</td></tr><tr><td>0 0 12 1/5 * ?</td><td>Fire at 12pm (noon) every 5 days every month, starting on the first
                                day of the month.</td></tr><tr><td>0 11 11 11 11 ?</td><td>Fire every November 11th at 11:11am.</td></tr></tbody></table><para>Pay attention to the effects of '?' and '*' in the day-of-week and
                    day-of-month fields!</para></section><section><title>Notes</title><itemizedlist><listitem><para> Support for specifying both a day-of-week and a day-of-month value is
                            not complete (you must currently use the '?' character in one of these
                            fields). </para></listitem><listitem><para> Be careful when setting fire times between mid-night and 1:00 AM -
                            "daylight savings" can cause a skip or a repeat depending on whether the
                            time moves back or jumps forward. </para></listitem></itemizedlist></section></section></chapter></book>