advanced-configuration.xml

<?xml version="1.0" encoding="UTF-8"?>
<chapter version="5.0" xml:id="advanced-configuration" xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xmlns:xi="http://www.w3.org/2001/XInclude"
         xmlns:svg="http://www.w3.org/2000/svg"
         xmlns:ns="http://docbook.org/ns/docbook"
         xmlns:mml="http://www.w3.org/1998/Math/MathML"
         xmlns:html="http://www.w3.org/1999/xhtml">
    <title>Advanced Configuration</title>
    <section id='controlling-synchronization'>
        <title>Controlling Synchronization</title>
        <para>
        The frequency of data synchronization is controlled by the coordination of a series of asynchronous events.   
        </para>    
        <para>
        After data is captured, the first event that occurs is the routing of the 
        captured <xref linkend="data" xrefstyle="select: title page"/>.  Data is routed by the <emphasis>Route Job</emphasis>.  It is a single background task that inserts into
        <xref linkend="data_event" xrefstyle="select: title page"/> and <xref linkend="outgoing_batch" xrefstyle="select: title page"/>.  The Route Job determines which nodes
        data will be sent to, as well as how much data will be batched together for transport.  When the <literal>start.route.job</literal> SymmetricDS property is set to 
        <literal>true</literal>, the frequency that routing occurs is controlled by the <literal>job.routing.period.time.ms</literal>.  Each time data is routed, the 
        <xref linkend="data_ref" xrefstyle="select: title page"/> table is updated with the id of the last contiguous data row to have been processed.  This is done so the query to find
        unrouted data is optimal. 
        </para>
        <para>
        After data is routed, it awaits transport to the target nodes.  Transport can occur when a client node is configured to pull data or when the host node is configured to push data.  These
        events are controlled by the <emphasis>Push</emphasis> and the <emphasis>Pull Jobs</emphasis>.  When the <literal>start.pull.job</literal> SymmetricDS property is set to 
        <literal>true</literal>, the frequency that data is pulled is controlled by the <literal>job.pull.period.time.ms</literal>.  When the <literal>start.push.job</literal> SymmetricDS property is set to 
        <literal>true</literal>, the frequency that data is pushed is controlled by the <literal>job.push.period.time.ms</literal>.  Data is extracted by channel from the source database's 
        <xref linkend="data" xrefstyle="select: title page"/> table at an interval controlled by the <literal>extract_period_millis</literal> column on the 
        <xref linkend="channel" xrefstyle="select: title page"/> table.  The <literal>last_extract_time</literal> is 
        always recorded, by channel, on the <xref linkend="node_channel_control" xrefstyle="select: title page"/> table for the host node's id.  When the Pull and Push Job run, if the extract period
        has not passed according to the last extract time, then the channel will be skipped for this run.  If the <literal>extract_period_millis</literal> is set to zero, data extraction will happen every time the jobs run.
        </para>
        <para>
        SymmetricDS also provides the ability to configure windows of time when synchronization is allowed.  This is done using the
        <xref linkend="node_group_channel_window" xrefstyle="select: title page"/> 
        table.  A list of allowed time windows can be specified for a node group and a channel.  If one or more windows exist, then data will only be extracted and transported if the time
        of day falls within the window of time specified.  The configured times are always for the target node's local time.  If the <literal>start_time</literal> is greater than the <literal>end_time</literal>, then the window crosses
        over to the next day.
        </para>
        <para>
        All data loading may be disabled by setting the <literal>dataloader.enable</literal> property to false.  This has the effect of not allowing incoming synchronizations, while allowing outgoing
        synchronizations.  All data extractions may be disabled by setting the <literal>dataextractor.enable</literal> property to false.  These properties can be controlled by inserting into the 
        root server's <xref linkend="parameter" xrefstyle="select: title page"/> table.  These properties affect every channel with the exception of the 'config' channel.  
        </para>
    </section>           
    <section id="multi-tier">
        <title>Multi-Tiered Synchronization</title>
        <para>
            As shown <link linkend="terminology-node-organization">previously</link>, at times there may be
            scenarios where data needs to flow through multiple tiers of nodes that
            are organized in a tree-like network with each tier requiring a different subset of data.  For example,
            you may have a system where the lowest tier may by a computer or device located in a store.  Those devices 
            may connect to a server located physically at that store.  Then the store server may communicate with 
            a corporate server for example.  In this case, the three tiers would be device, store, and corporate.
            Each tier is typically represented by a node group.  Each node in 
            the tier would belong to the node group representing that tier.   
        </para>
        <para>
            A node will always push and pull data to other node groups according to the node group link configuration.
            A node can only pull and push data to other nodes that are represented <literal>node</literal> table in its database and 
            having <literal>sync_enabled = 1</literal>.
            Because of this, a tree-like 
            hierarchy of nodes can be created by having only a subset of nodes belonging to the same node group represented at the different branches of the tree.  
        </para>
        <para>
            If auto registration is turned <emphasis>off</emphasis>, then this setup must occur manually by opening registration 
            for the desired nodes at the desired parent node and by configuring each node's <literal>registration.url</literal>
             to be the parent node's URL.  
            The parent node is always tracked by the setting of the parent's <literal>node_id</literal> in the <literal>created_at_node_id</literal> column of the new node.  
            When a node registers and downloads its configuration it is always provided the configuration for nodes 
            that might register with the node itself based on the Node Group Links defined in the parent node.
        </para>
               
    </section>
    <section id='registration-redirect'>
        <title>Registration Redirect</title>    
        <para>
            When deploying a multi-tiered system it may be advantageous to have only one registration server, even though the parent node of a registering node
            could be any of a number of nodes in the system.  In SymmetricDS the parent node is always the node that a child registers with.  The 
            <xref linkend="registration_redirect" xrefstyle="select: title page"/> table allows a single node, usually the root server in the network, to
            redirect registering nodes to their true parents.  It does so based on a mapping found in the table of the external id (<literal>registrant_external_id</literal>) to the parent's node 
            id (<literal>registration_node_id</literal>).
        </para>
        <para>
            For example, if it is desired to have a series of regional servers that workstations at retail stores get assigned to based on their <literal>external_id</literal>, the store number, then
            you might insert into <xref linkend="registration_redirect" xrefstyle="select: title page"/> the store number as the <literal>registrant_external_id</literal> and the <literal>node_id</literal> of
            the assigned region as the <literal>registration_node_id</literal>.  When a workstation at the store registers, the root server send an HTTP redirect to the <literal>sync_url</literal> of the node 
            that matches the <literal>registration_node_id</literal>. 
        </para>
    </section>
    <section id="bi-direction-sync">
        <title>Bi-Directional Synchronization</title>
        <para>
            SymmetricDS allows tables to be synchronized bi-directionally.  Note that an outgoing 
            synchronization does not process changes during an incoming synchronization on the same node unless the trigger 
            was created with the <literal>sync_on_incoming_batch</literal> flag set.  If the <literal>sync_on_incoming_batch</literal> flag
            is set, then update loops are prevented by a feature that is available in most database dialects.  
            More specifically, during an incoming synchronization the source <literal>node_id</literal> is put into a database session variable that is 
            available to the database trigger.  Data events are not generated if the target <literal>node_id</literal> 
            on an outgoing synchronization is equal to the source <literal>node_id</literal>.  
        </para>     
        <para>
            By default, only the columns that changed will be updated in the target system.
        </para>  
        <para>
            More complex conflict resolution strategies can be accomplished by using the 
            <literal>IDataLoaderFilter</literal> extension point which has access to both 
            old and new data.
        </para>         
    </section>         
    <section id="dead-triggers">
        <title>Dead Triggers</title>
        <para>
            Normally a Trigger is specified to capture data changes to a table and send them to
            a target Node Group.  A "dead" Trigger is one that does not capture data changes.
            In other words, the <literal>sync_on_insert</literal>, <literal>sync_on_update</literal>, and <literal>sync_on_delete</literal> properties
            for the Trigger are all set to false.  However, because the Trigger is specified,
             it <emphasis>will</emphasis>
            be included in the initial load of data for target Nodes.
        </para>
        <para>
            A dead Trigger might be used to load a read-only lookup table, for example.  It could also 
            be used
            to load a table that needs populated with example or default data.
            Another use is a recovery load of data for tables that have a single direction
            of synchronization.  For example, a retail store records sales transaction that
            synchronize in one direction by trickling back to the central office.
            If the retail store needs to recover all the sales transactions from the central office,
            they can be sent
            are part of an initial load from the central office by setting up dead Triggers
            that "sync" in that direction.
        </para>
        <para>
            The following SQL statement sets up a non-syncing dead Trigger that sends
            the <literal>sale_transaction</literal> table to the "store" Node Group from the "corp" Node Group during
            an initial load.
            <programlisting>
<![CDATA[
insert into sym_trigger (TRIGGER_ID,SOURCE_CATALOG_NAME,
  SOURCE_SCHEMA_NAME,SOURCE_TABLE_NAME,CHANNEL_ID,
  SYNC_ON_UPDATE,SYNC_ON_INSERT,SYNC_ON_DELETE,
  SYNC_ON_INCOMING_BATCH,NAME_FOR_UPDATE_TRIGGER,
  NAME_FOR_INSERT_TRIGGER,NAME_FOR_DELETE_TRIGGER,
  SYNC_ON_UPDATE_CONDITION,SYNC_ON_INSERT_CONDITION,
  SYNC_ON_DELETE_CONDITION,EXTERNAL_SELECT,
  TX_ID_EXPRESSION,EXCLUDED_COLUMN_NAMES,
  CREATE_TIME,LAST_UPDATE_BY,LAST_UPDATE_TIME) 
  values ('SALE_TRANSACTION_DEAD',null,null,
  'SALE_TRANSACTION','transaction',
  0,0,0,0,null,null,null,null,null,null,null,null,null,
  current_timestamp,'demo',current_timestamp);

insert into sym_router (ROUTER_ID,TARGET_CATALOG_NAME,TARGET_SCHEMA_NAME,
  TARGET_TABLE_NAME,SOURCE_NODE_GROUP_ID,TARGET_NODE_GROUP_ID,ROUTER_TYPE,
  ROUTER_EXPRESSION,SYNC_ON_UPDATE,SYNC_ON_INSERT,SYNC_ON_DELETE,
  CREATE_TIME,LAST_UPDATE_BY,LAST_UPDATE_TIME) 
  values ('CORP_2_STORE',null,null,null,
  'corp','store',null,null,1,1,1,
  current_timestamp,'demo',current_timestamp);
   
insert into sym_trigger_router (TRIGGER_ID,ROUTER_ID,INITIAL_LOAD_ORDER,
  INITIAL_LOAD_SELECT,CREATE_TIME,LAST_UPDATE_BY,LAST_UPDATE_TIME) 
  values ('SALE_TRANSACTION_DEAD','CORP_2_REGION',100,null,
   current_timestamp,'demo',current_timestamp);
   ]]></programlisting>
        </para>
    </section>
    <section id='jms-publishing'>
        <title>JMS Publishing</title>    
        <para>
            With the proper configuration SymmetricDS can publish XML messages of captured data changes to 
            JMS during routing or transactionally while data loading synchronized data into a target database.
            The following explains how to publish to JMS during synchronization to the target database. 
       </para>
       <para>     
            The XmlPublisherDataLoaderFilter is a
            <link linkend="extensions-data-loader-filter">IDataLoaderFilter</link> that may be configured to 
            publish specific tables as an XML message to a JMS provider.
            See <link linkend="extensions">extension points</link> for information on how 
            to configure an extension point.  If the publish to JMS fails, the batch will be marked in error, 
            the loaded data for the batch will be rolled back
            and the batch will be retried during the next synchronization run.            
        </para>
        <para>
        The following is an example extension point configuration that will publish four tables in XML with a root 
        tag of <emphasis>'sale'</emphasis>.  Each XML message will be grouped by the batch and the column names identified by
        the groupByColumnNames property which have the same values.
                <programlisting><![CDATA[<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans 
           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
           http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-3.0.xsd">
 
    <bean id="publishingFilter" 
      class="org.jumpmind.symmetric.integrate.XmlPublisherDataLoaderFilter">
        <property name="xmlTagNameToUseForGroup" value="sale"/>
        <property name="tableNamesToPublishAsGroup">
            <list>
               <value>SALE_TX</value>
               <value>SALE_LINE_ITEM</value>
               <value>SALE_TAX</value>
               <value>SALE_TOTAL</value>
            </list>            
        </property>
        <property name="groupByColumnNames">
            <list>
               <value>STORE_ID</value>
               <value>BUSINESS_DAY</value>
               <value>WORKSTATION_ID</value>
               <value>TRANSACTION_ID</value>
            </list>                      
        </property>
        <property name="publisher">
           <bean class="org.jumpmind.symmetric.integrate.SimpleJmsPublisher">
               <property name="jmsTemplate" ref="definedSpringJmsTemplate"/>
           </bean>
        </property>        
    </bean>     
</beans>]]></programlisting>        
        </para>
        <para>
          The publisher property on the XmlPublisherDataLoaderFilter takes an interface of type IPublisher.  The implementation
          demonstrated here is an implementation that publishes to JMS using Spring's 
          <ulink url="http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/jms.html#jms-jmstemplate">JMS template</ulink>.
          Other implementations of IPublisher could easily publish the XML to other targets like an HTTP server, the file system or secure copy it to another server.
        </para>
        <para>
          The above configuration will publish XML similiar to the following:
            <programlisting><![CDATA[<?xml version="1.0" encoding="UTF-8"?>
<sale xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  id="0012010-01-220031234" nodeid="00001" time="1264187704155">
  <row entity="SALE_TX" dml="I">
    <data key="STORE_ID">001</data>
    <data key="BUSINESS_DAY">2010-01-22</data>
    <data key="WORKSTATION_ID">003</data>
    <data key="TRANSACTION_ID">1234</data>
    <data key="CASHIER_ID">010110</data>
  </row>        
  <row entity="SALE_LINE_ITEM" dml="I">
    <data key="STORE_ID">001</data>
    <data key="BUSINESS_DAY">2010-01-22</data>
    <data key="WORKSTATION_ID">003</data>
    <data key="TRANSACTION_ID">1234</data>
    <data key="SKU">9999999</data>  
    <data key="PRICE">10.00</data>
    <data key="DESC" xsi:nil="true"/>
  </row>        
  <row entity="SALE_LINE_ITEM" dml="I">
    <data key="STORE_ID">001</data>
    <data key="BUSINESS_DAY">2010-01-22</data>
    <data key="WORKSTATION_ID">003</data>
    <data key="TRANSACTION_ID">1234</data>
    <data key="SKU">9999999</data>  
    <data key="PRICE">10.00</data>
    <data key="DESC" xsi:nil="true"/>
  </row>
  <row entity="SALE_TAX" dml="I">
    <data key="STORE_ID">001</data>
    <data key="BUSINESS_DAY">2010-01-22</data>
    <data key="WORKSTATION_ID">003</data>
    <data key="TRANSACTION_ID">1234</data>
    <data key="AMOUNT">1.33</data>  
  </row>
  <row entity="SALE_TOTAL" dml="I">
    <data key="STORE_ID">001</data>
    <data key="BUSINESS_DAY">2010-01-22</data>
    <data key="WORKSTATION_ID">003</data>
    <data key="TRANSACTION_ID">1234</data>
    <data key="AMOUNT">21.33</data>  
  </row>
</sale>
            ]]></programlisting>     
            To publish JMS messages during routing
            the same pattern is valid, with the exception that the extension point would be the XmlPublisherDataRouter and the router 
            would be configured by setting the <literal>router_type</literal> of a <xref linkend="router" xrefstyle="select: title page"/> to the Spring bean
            name of the registered extension point.  Of course, the router would need to be linked through <xref linkend="trigger_router" xrefstyle="select: title page"/>s
            to each <xref linkend="trigger" xrefstyle="select: title page"/>  table that needs published.                  
        </para>
    </section>     
    <section id="purge">
        <title>Database Purging</title>
        <para>
            Purging is the act of cleaning up captured data that is no longer needed in SymmetricDS's runtime tables.  
            Data is purged through
            delete statements by the <emphasis>Purge Job</emphasis>.  Only data that has been successfully synchronized will be purged.  Purged tables include:
            <itemizedlist>
                <listitem>
                   <xref linkend="data" xrefstyle="select: title page"/>
                </listitem>
                <listitem>
                    <xref linkend="data_event" xrefstyle="select: title page"/>
                </listitem>
                <listitem>
                  <xref linkend="outgoing_batch" xrefstyle="select: title page"/>
                </listitem>
                <listitem>
                    <xref linkend="incoming_batch" xrefstyle="select: title page"/>
                </listitem>
                <listitem>
                   <xref linkend="statistic" xrefstyle="select: title page"/>
                </listitem>                
            </itemizedlist>
            The purge job is enabled by the <literal>start.purge.job</literal> SymmetricDS property.  The job runs periodically according to the 
            <literal>job.purge.period.time.ms</literal> property.  The default period is to run every ten minutes.  
        </para>      
        <para>
            Two retention period properties
            indicate how much history SymmetricDS will retain before purging.  The <literal>purge.retention.minutes</literal> property indicates the period
            of history to keep for synchronization tables.  The default value is 5 days.
            The <literal>statistic.retention.minutes</literal> property
            indicates the period of history to keep for statistics.  The default value is also 5 days.            
        </para>
        <para>
            The purge properties should be adjusted according to how much data is flowing through the system and the amount of storage space the database has.
            For an initial deployment it is recommended that the purge properties be kept at the defaults, since it is often helpful to be able to look at 
            the captured data in order to triage problems and profile the synchronization patterns.  When scaling up to more nodes, it is recomended that the 
            purge parameters be scaled back to 24 hours or less.  
        </para>
        
    </section>
    <section id="temporary-files">
        <title>Temporary Files</title>
        <para>
        SymmetricDS creates temporary extraction and data load files with the CSV payload of a synchronization when
        the value of the <literal>stream.to.file.threshold.bytes</literal> SymmetricDS property has been reached.  Before reaching the threshold, files 
        are streamed to/from memory.  The default threshold value is 32,767 bytes. This feature may be turned off by setting the <literal>stream.to.file.enabled</literal> 
        property to false.
        </para>
        <para>
        SymmetricDS creates these temporary files in the directory specified by the <literal>java.io.tmpdir</literal> Java System property.  When  
        SymmmetricDS starts up, stranded temporary files are aways cleaned up.  Files will only be stranded if the SymmetricDS engine is force killed.
        </para>
        <para>
        The location of the temporary directory may be changed by setting the Java System property passed into the Java program at startup.  For example,
        <programlisting>
  -Djava.io.tmpdir=/home/.symmetricds/tmp
        </programlisting>   
        </para>
    </section>    
    <section id="clustering">
        <title>Clustering</title>
        <para>
        A single SymmetricDS node may be clustered across a series of instances, creating a web farm.  A node might be clustered to provide load balancing and failover, for example.
        </para>
        <para>
        When clustered, a hardware load balancer is typically used
        to round robin client requests to the cluster.  The load balancer should be configured for stateless connections.  
        Also, the <link linkend='basic-properties'>sync.url</link>
        SymmetricDS property should be set to the URL of the load balancer.  
        </para>
        <para>
        If the cluster will be running any of the SymmetricDS jobs, then the <literal>cluster.lock.enabled</literal> property should be set to <literal>true</literal>. 
        By setting this property to true, SymmetricDS will use a row in the <link linkend="lock">lock</link> table as a semaphore to make sure that only one instance at a time
        runs a job.  When a lock is acquired, a row is updated in the lock table with the time of the lock and the server id of the locking job.  The lock time is set back to null
        when the job is finished running.  Another instance of SymmetricDS cannot aquire a lock until the locking instance (according to the server id) releases the lock.  If an 
        instance is terminated while the lock is still held, an instance with the same server id is allowed to reaquire the lock.  If the locking instance remains down, the lock can be 
        broken after a period of time, specified by the <literal>cluster.lock.timeout.ms</literal> property, has expired.  Note that if the job is still running and the lock
        expires, two jobs could be running at the same time which could cause database deadlocks. 
        </para>
        <para>
        By default, the locking server id is the hostname of the server.  If two clustered instances are running on the same server, then the <literal>cluster.server.id</literal> property 
        may be set to indicate the name that the instance should use for its server id.
        </para>
        <para>
        When deploying SymmetricDS to an application server like Tomcat or JBoss, no special session clustering needs to be configured for the application server.  
        </para>
    </section>   
    <section id='logging'>
        <title>Logging Configuration</title>    
        <para>
        The standalone SymmetricDS installation uses <ulink url="http://logging.apache.org/log4j/1.2/index.html">Log4J</ulink> for logging.  The configuration file is  <literal>conf/log4j.xml</literal>.
        The <literal>log4j.xml</literal> file has hints as to what logging can be enabled for useful, finer-grained logging.
        </para>
        <para>
        SymmetricDS proxies all of its logging through <ulink url="http://commons.apache.org/logging/">Commons Logging</ulink>.  When deploying to an application server, if Log4J is not 
        being leveraged, then the general rules for for Commons Logging apply.
        </para>
    </section> 
    <section id="extensions">
        <title>Extension Points</title>
        <para>
             SymmetricDS may be extended via a plug-in like architecture where extension point interfaces 
             may be implemented by a custom class and registered with the synchronization engine.  All supported extension 
             points extend the IExtensionPoint interface.  The currently available extension points are documented in the following sections.  
        </para>
        <para>
             When the synchronization engine starts up, a Spring 
             post processor searches the Spring ApplicationContext for any registered classes which implement 
             IExtensionPoint.  An IExtensionPoint designates whether it should be auto registered or not.  If the extension point 
             is to be auto registered then the post processor registers the known interface with the appropriate service.
        </para>
        <para>
             The INodeGroupExtensionPoint interface may be optionally implemented to designate that auto registered 
             extension points should only be auto registered with specific node groups.
             <programlisting><![CDATA[/**
 * Only apply this extension point to the 'root' node group.
 */
 public String[] getNodeGroupIdsToApplyTo() {
     return new String[] { "root" };
 }
]]></programlisting>             
        </para>
        <para>
             SymmetricDS will look for Spring configured extensions in the application Classpath by importing any Spring 
             XML configuration files found matching the following pattern: <literal>META-INF/services/symmetric-*-ext.xml</literal>.  When packaged in
             a jar file the <literal>META-INF</literal> directory should be at the root of the jar file.  When packaged in a war file, the <literal>META-INF</literal> directory
             should be in the <literal>WEB-INF/classes</literal> directory.
        </para>
        <section id="parameter-filter">
            <title>IParameterFilter</title>
            <para>
                Parameter values can be specified in code using a parameter filter.  Note that there can be only one parameter
                filter per engine instance.  The IParameterFilter replaces the deprecated IRuntimeConfig from prior releases.
                <programlisting><![CDATA[public class MyParameterFilter 
    implements IParameterFilter, INodeGroupExtensionPoint {

    /**
     * Only apply this filter to stores
     */
    public String[] getNodeGroupIdsToApplyTo() {
        return new String[] { "store" };
    }

    public String filterParameter(String key, String value) {
        // look up a store number from an already existing properties file.
        if (key.equals(ParameterConstants.EXTERNAL_ID)) {
            return StoreProperties.getStoreProperties().
              getProperty(StoreProperties.STORE_NUMBER);
        } 
        return value;
    }

    public boolean isAutoRegister() {
        return true;
    }

}]]></programlisting> 
            </para>
        </section>        
        <section id="extensions-data-loader-filter">
            <title>IDataLoaderFilter</title>         
            <para>
                Data can be filtered as it is loaded into the target database.  It can also be
                filtered when
                it is extracted from the source database.
            
                As data is loaded into the target database, a filter can change the
                data in a column or save it somewhere else.  It can also specify by the
                return value of the function call that the data loader should continue on 
                and load the data (by returning true) or ignore it (by returning false). One 
                possible use of the filter might be to
                route credit card data to a secure database and blank it out as it loads 
                into a less-restricted reporting database.
            </para>
            <para>
                An IDataLoaderContext is passed to each of the callback methods.  A new 
                context is created for each synchronization.  The context provides methods to 
                lookup column indexes by column name, get table meta data, and access to 
                old data if the <literal>sync_column_level</literal> flag is enabled.  The context also provides a means 
                to share data during a synchronization between different rows of data that are 
                committed in a  database transaction and are in the same channel.  It does so by 
                providing a context cache which can be populated by the extension point.
            </para>  
            <para>
                Many times the IDataLoaderFilter will be combined with the IBatchListener.  The 
                XmlPublisherFilter (in the <literal>org.jumpmind.symmetric.ext</literal> package) is a good example 
                of using the combination of the two extension points in order to create XML messages 
                to be published to JMS.
            </para>          
            <para>
                A class implementing the IDataLoaderFilter interface is injected onto the
                DataLoaderService in order to receive callbacks when data is inserted,
                updated, or deleted.
                
                <programlisting><![CDATA[public MyFilter implements IDataLoaderFilter {
                
    public boolean isAutoRegister() {
        return true;
    }
 
    public boolean filterInsert(IDataLoaderContext context,
        String[] columnValues) {
        return true;
    }
    
    public boolean filterUpdate(IDataLoaderContext context, 
        String[] columnValues, String[] keyValues) {
        return true;
    }
    
    public void filterDelete(IDataLoaderContext context, 
        String[] keyValues) {
        return true;
    }

}]]></programlisting>
            </para>
            <para>
                The filter class is specified as a Spring-managed bean.  A custom Spring XML file
                is specified as follows in a jar at <literal>META-INF/services/symmetric-myfilter-ext.xml</literal>.
                
                <programlisting><![CDATA[<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans 
           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
           http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-3.0.xsd">
 
    <bean id="myFilter" class="com.mydomain.MyFilter"/>
     
</beans>]]></programlisting>
            </para>
        </section>
        <section id="extensions-table-column-filter">
            <title>ITableColumnFilter</title>
            <para>
            Implement this extension point to filter out specific columns from
            use by the dataloader. Only one column filter may be added per target table.
            </para>
        </section>
        <section id="extensions-batch-listener">
            <title>IBatchListener</title>
            <para>
            This extension point is called whenever a batch has completed loading but before
            the transaction has committed.
            </para>
        </section>
        <section id="extensions-acknowledge-event-listener">
            <title>IAcknowledgeEventListener</title>
            <para>
            Implement this extension point to receive callback events when a batch is acknowledged.  
            The callback for this listener happens at the point of extraction.
            </para>
        </section>                
        <section id="extensions-reload-listener">
            <title>IReloadListener</title>
            <para>
            Implement this extension point to listen in and take
            action before or after a reload is requested for a Node.  The callback for this listener
            happens at the point of extraction.
            </para>
        </section>                
        <section id="extensions-extractor-filter">
            <title>IExtractorFilter</title>
            <para>
            This extension point is called after data has been extracted, but before it has been streamed.  It
            has the ability to inspect each row of data to take some action and indicate, if necessary, that the
            row should not be streamed.
            </para>
        </section>
        <section id="extensions-sync-url-extension">
            <title>ISyncUrlExtension</title>
            <para>
             This extension point is used to select an appropriate URL based on
             the URI provided in the <literal>sync_url</literal> column of <literal>sym_node</literal>.
            </para>
            <para>
             To use this extension point configure the sync_url for a node with the
             protocol of ext://beanName. The beanName is the name you give the extension
             point in the extension xml file.
            </para>
        </section>        
        <section id="extensions-node-id-generator">
            <title>INodeIdGenerator</title>
            <para>
             This extension point allows SymmetricDS users to implement their own algorithms for how 
             node ids and passwords are generated or selected during the registration process.  There may be 
             only one node generator per SymmetricDS instance.
            </para>
        </section>
        <section id="extensions-trigger-creation-listener">
            <title>ITriggerCreationListener</title>
            <para>
            Implement this extension point to get status callbacks during trigger creation.
            </para>
        </section>       
        <section id="extensions-batch-algorithm">
            <title>IBatchAlgorithm</title>
            <para>
            Implement this extension point and set the name of the Spring bean on the batch_algorithm column of the Channel table to use.
            This extension point gives fine grained control over how a channel is batched.
            </para>
        </section>                   
        <section id="extensions-data-router">
            <title>IDataRouter</title>
            <para>
            Implement this extension point and set the name of the Spring bean on the router_type column
            of the Router table to use.  This extension point gives the ability to programatically decide
            which nodes data should be routed to.
            </para>
        </section>  
        <section id="extensions-heartbeat-listener">
            <title>IHeartbeatListener</title>
            <para>
            Implement this extension point to get callbacks during the heartbeat job.
            </para>
        </section>
        <section id="extensions-offline-client-listener">
            <title>IOfflineClientListener</title>
            <para>
            Implement this extension point to get callbacks for offline events on client nodes.
            </para>
        </section>
        <section id="extensions-offline-server-listener">
            <title>IOfflineServerListener</title>
            <para>
            Implement this extension point to get callbacks for offline events detected on a server node during monitoring of client nodes.
            </para>
        </section>
        <section id="extensions-node-password">
            <title>INodePasswordFilter</title>
            <para>
            Implement this extension point to intercept the saving and rendering of the node password.
            </para>
        </section>        
        <section id="extensions-servlets">
            <title>IServletExtension</title>
            <para>
            Implement this extension point to allow additional Servlets to be registered with SymmetricDS.  This is probably only 
            useful if SymmetricDS is running in standalone or embedded mode.
            </para>
        </section>                      
    </section>
    <section id="encrypted-passwords">
        <title>Encrypted Passwords</title>
        <para>
            The <literal>db.user</literal> and <literal>db.password properties</literal> will accept encrypted text, which protects
            against casual observation.  The text is prefixed with <literal>enc:</literal> to indicate
            that it is encrypted.  To encrypt text, use the following command:
        </para>
        <para>
            <command>sym -e secret</command>
        </para>
        <para>
            The text is encrypted by the cipher defined as alias "sym.secret" in the 
            Java keystore.  The keystore is specified by the "sym.keystore.file" system property, which
            defaults to <filename class="filename">security/keystore</filename>.
            If a cipher is not found, a default cipher using Triple DES with a random password
            is generated.
        </para>
    </section>
    <section id="secure-transport">
        <title>Secure Transport</title>
        <para>
            By specifying the "https" protocol for a URL, SymmetricDS will communicate over
            Secure Sockets Layer (SSL) for an encrypted transport.  The following properties
            need to be set with "https" in the URL:
            <variablelist>
                <varlistentry>
                    <term>
                        <command>sync.url</command>
                    </term>
                    <listitem>
                        <para>
                            This is the URL of the current node, so if you want to force other
                            nodes to communicate over SSL with this node, you specify "https" in the URL.
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>
                        <command>registration.url</command>
                    </term>
                    <listitem>
                        <para>
                            This is the URL where the node will connect for registration when it 
                            first starts up.  To protect the registration with SSL, you specify
                            "https" in the URL.
                        </para>
                    </listitem>
                </varlistentry>
            </variablelist>
            For incoming HTTPS connections, SymmetricDS depends on the webserver where
            it is deployed, so the webserver must be configured for HTTPS.
            As a standalone deployment, the "sym" launcher command provides options for 
            enabling HTTPS support.
        </para>
        <section id="secure-transport-sym">
            <title>Sym Launcher</title>
            <para>
                The "sym" launch command uses Jetty as an embedded web server.
                Using command line options, the web server can be told to listen for 
                HTTP, HTTPS, or both.
            </para>
            <para>
                <command>sym --port 8080 --server</command>
            </para>
            <para>
                <command>sym --secure-port 8443 --secure-server</command>
            </para>
            <para>
                <command>sym --port 8080 --secure-port 8443 --mixed-server</command>
            </para>
        </section>
        <section id="secure-transport-tomcat">
            <title>Tomcat</title>
            <para>
                If you deploy SymmetricDS to Apache Tomcat, it can be secured by editing the
                <filename class="filename">TOMCAT_HOME/conf/server.xml</filename>
                configuration file.  There is already a line that can be uncommented
                and changed to the following:
                
                <programlisting>
<![CDATA[<Connector port="8443" protocol="HTTP/1.1" SSLEnabled="true" 
  maxThreads="150" scheme="https" secure="true" 
  clientAuth="false" sslProtocol="TLS"
  keystoreFile="/symmetric-ds-1.x.x/security/keystore" />]]></programlisting>
            </para>
        </section>
        <section id="secure-transport-keystore">
            <title>Keystores</title>
            <para>
                When SymmetricDS connects to a URL with HTTPS, Java checks the validity of the
                certificate using the built-in trusted keystore located at
                <filename class="filename">JRE_HOME/lib/security/cacerts</filename>.
                The "sym" launcher command overrides the trusted keystore to use its own
                trusted keystore instead, which is located at
                <filename class="filename">security/cacerts</filename>.
                This keystore contains the certificate aliased as "sym" for use in testing
                and easing deployments.                
                The trusted keystore can be overridden
                by specifying the <literal>javax.net.ssl.trustStore</literal> system property.
            </para>
            <para>
                When SymmetricDS is run as a secure server with the "sym" launcher,
                it accepts incoming requests using the key installed in the keystore
                located at
                <filename class="filename">security/keystore</filename>.
                The default key is provided for convenience of testing, but should be
                re-generated for security.
            </para>
        </section>
        <section id="secure-transport-keys">
            <title>Generating Keys</title>
            <para>
                To generate new keys and install a server certificate, use the
                following steps:
            </para>
            <procedure>
                <step>
                    <para>
                        Open a command prompt and navigate to the
                        <filename class="directory">security</filename>
                        subdirectory of your SymmetricDS installation.
                    </para>
                </step>
                <step>
                    <para>Delete the old key pair and certificate.</para>
                    <para>
                        <command>keytool -keystore keystore -delete -alias sym</command>
                    </para>
                    <para>
                        <command>keytool -keystore cacerts -delete -alias sym</command>
                    </para>
                    <programlisting><![CDATA[Enter keystore password:  changeit]]></programlisting>
                </step>
                <step>
                    <para>Generate a new key pair.</para>
                    <para>
                        <command>keytool -keystore keystore -alias sym -genkey -keyalg RSA -validity 10950</command>
                    </para>
                    <programlisting>
<![CDATA[Enter keystore password:  changeit
What is your first and last name?
  [Unknown]:  localhost
What is the name of your organizational unit?
  [Unknown]:  SymmetricDS
What is the name of your organization?
  [Unknown]:  JumpMind
What is the name of your City or Locality?
  [Unknown]:
What is the name of your State or Province?
  [Unknown]:
What is the two-letter country code for this unit?
  [Unknown]:
Is CN=localhost, OU=SymmetricDS, O=JumpMind, L=Unknown, ST=Unknown, C=Unknown
correct?
  [no]:  yes

Enter key password for <sym>
        (RETURN if same as keystore password):]]></programlisting>
                </step>
                <step>
                    <para>Export the certificate from the private keystore.</para>
                    <para>
                        <command>keytool -keystore keystore -export -alias sym -rfc -file sym.cer</command>
                    </para>
                </step>
                <step>
                    <para>Install the certificate in the trusted keystore.</para>
                    <para>
                        <command>keytool -keystore cacerts -import -alias sym -file sym.cer</command>
                    </para>
                </step>
            </procedure>
        </section>
    </section>
    <section id="basic-auth">
        <title>Basic Authentication</title>
        <para>
            SymmetricDS supports basic authentication for client and server nodes. 
            To configure a client node to use basic authentication when communicating with a server node, 
            specify the following startup parameters:
        </para>
            <variablelist>
                <varlistentry>
                    <term>
                        <command>http.basic.auth.username</command>
                    </term>
                    <listitem>
                        <para>
                            username for client node basic authentication.
                            [&#xA0;Default:&#xA0;]
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>
                        <command>http.basic.auth.password</command>
                    </term>
                    <listitem>
                        <para>
                            password for client node basic authentication.
                            [&#xA0;Default:&#xA0;]
                        </para>
                    </listitem>
                </varlistentry>
            </variablelist>
        <para>
            The SymmetricDS Standalone and Embedded Server also support basic authentication.
            This feature is enabled by specifying the basic authentication username and
            password using the following startup parameters:
        </para>
            <variablelist>
                <varlistentry>
                    <term>
                        <command>embedded.webserver.basic.auth.username</command>
                    </term>
                    <listitem>
                        <para>
                            username for basic authentication for an embedded server
                            or standalone server node.
                            [&#xA0;Default:&#xA0;]
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>
                        <command>embedded.webserver.basic.auth.password</command>
                    </term>
                    <listitem>
                        <para>
                            password for basic authentication for an embedded server
                            or standalone server node.
                            [&#xA0;Default:&#xA0;]
                        </para>
                    </listitem>
                </varlistentry>
            </variablelist>
        <para>
            If the server node is deployed to Tomcat or another application server as a WAR or EAR file, then 
            basic authentication is setup with the standard configuration in the WEB.xml file. 
        </para>
    </section>
</chapter>