SymmetricDS Pro 3.14 User Guide

SymmetricDS is written in Java and requires a Java Runtime Environment (JRE) Standard Edition (SE) or Java Development Kit (JDK) Standard Edition (SE) version 8.0 or above. Most major operating systems and databases are supported. See the list of supported databases in the Database Compatibility section. The minimum operating system requirements are:

The memory, disk, and CPU requirements increase with the number of connected clients and the amount of data being synchronized. The best way to size a server is to simulate synchronization in a lower environment and benchmark data loading. However, a rule of thumb for servers is one server-class CPU with 2 GB of memory for every 500 MB/hour of data transfer and 350 clients. Multiple servers can be used as a cluster behind a load balancer to achieve better performance and availability.

SymmetricDS Pro is accessed from a web console, which requires one of the following supported web browsers:

A node is responsible for synchronizing the data from a database or file system with other nodes in the network using HTTP. Nodes are assigned to one of the node Groups that are configured together as a unit. The node groups are linked together with Group Links to define either a push or pull communication. A pull causes one node to connect with other nodes and request changes that are waiting, while a push causes one node to connect with other nodes when it has changes to send.

Each node is connected to a database with a Java Database Connectivity (JDBC) driver using a connection URL, username, and password. While nodes can be separated across wide area networks, the database a node is connected to should be located nearby on a local area network for the best performance. Using its database connection, a node creates tables as a Data Model for configuration settings and runtime operations. The user populates configuration tables to define the synchronization and the runtime tables capture changes and track activity. The tables to sync can be located in any Catalog and Schema that are accessible from the connection, while the files to sync can be located in any directory that is accessible on the local server.

At startup, SymmetricDS looks for Node Properties Files and starts a node for each file it finds, which allows multiple nodes to run in the same instance and share resources. The property file for a node contains its external ID, node group, registration server URL, and database connection information. The external ID is the name for a node used to identify it from other nodes. One node is configured as the registration server where the master configuration is stored. When a node is started for the first time, it contacts the registration server using a registration process that sends its external ID and node group. In response, the node receives its configuration and a node password that must be sent as authentication during synchronization with other nodes.

Each subsystem in the node is responsible for part of the data movement and is controlled through configuration. Data flows through the system in the following steps:

SymmetricDS offers a rich set of features with flexible configuration for large scale deployment in a mixed environment with multiple systems.

SymmetricDS is a feature-rich data synchronization solution that focuses on ease of use, openness, and flexibility. The software encourages interoperability and accessibility for users and developers with the availability of source code, an application programming interface (API), and a data model supported by documentation. Configuration includes a powerful set of options to define node topology, communication direction, transformation of data, and integration with external systems. Through scripts and Java code, the user can also extend functionality with custom behavior. With a central database for setup and runtime information, the user has one place to configure, manage, and troubleshoot synchronization, with changes taking immediate effect across the network.

The trigger-based data capture system is easy to understand and widely supported by database systems. Table synchronization can be setup by users and application developers without requiring a database administrator to modify the server. Triggers are database objects written in a procedural language, so they are open for examination, and include flexible configuration options for conditions and customization. Some overhead is associated with triggers, but they perform well for applications of online transaction processing, and their benefits of flexibility and maintenance outweigh the cost for most scenarios.

Using an architecture based on web server technology, many simultaneous requests can be handled at a central server, with proven deployments in production supporting more than ten thousand client nodes. Large networks of nodes can be grouped into tiers for more control and efficiency, with each group synchronizing data to the next tier. Data loading is durable and reliable by tracking batches in transactions and retrying of faults for automatic recovery, making it a low maintenance system.

SymmetricDS Pro is commercial software that is licensed, not sold. It is subject to the terms of the End User License Agreement (EULA) and any accompanying JumpMind Support Contract. See the standard SymmetricDS Pro license for reference, but your agreement with JumpMind may be different.

The SymmetricDS Pro setup program is an executable JAR file that can run on any system with a Java Runtime Environment (JRE). See System Requirements for prerequisites. Download the setup program from SymmetricDS Pro Downloads.

Run the setup program:

To continue setup and configuration of SymmetricDS, refer to the Setup section.

SymmetricDS can be configured to start automatically when the system boots, running as a Windows service or Linux/Unix daemon. A wrapper process starts SymmetricDS and monitors it, so it can be restarted if it runs out of memory or exits unexpectedly. The wrapper writes standard output and standard error to the logs/wrapper.log file.

For SymmetricDS Pro, you may have already installed as a service, so this section will show you how to manually install the service from command line.

A single SymmetricDS node can be deployed across a series of servers to cooperate as a cluster. A node can be clustered to provide load balancing and high availability.

Each node in the cluster shares the same database. A separate hardware or software load balancer is required to receive incoming requests and direct them to one of the backend nodes. Use the following steps to setup a cluster:

With the cluster.lock.enabled property set to true, jobs will acquire an entry in the LOCK table to ensure that only one instance of the job runs across the cluster. 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 locking server ID defaults to the host name, but it can specified with the cluster.server.id property if nodes are running on the same server. Another instance of the job cannot acquire a lock until the locking instance releases the lock and sets the lock time back to null. If an instance is terminated while the lock is still held, an instance with the same server ID is allowed to re-acquire the lock. If the locking instance remains down, the lock can be broken after it expires, specified by the cluster.lock.timeout.ms property. Jobs refresh their lock periodically as they run, which prevents a lock from expiring due to a long run time.

The load balancer should be configured to use sticky sessions if the cluster will receive push synchronization. Push connections first request a reservation from the target node and then connect again using the reservation to push changes. Sticky sessions ensures that the push request is sent to the same server where the reservation is held.

Staging is writing batches to disk before sending over the network, which can use local disk or a shared network drive. Staging can improve performance by reducing the time that resources are held open in the database and by extracting batches before they are served. To use local staging in a cluster, disable the initial.load.use.extract.job.enabled property so the initial load will extract batches on the node serving the request, rather than extracting in the background on a different node. To use shared staging in a cluster, set the staging.dir property to the directory path of the network drive and enable the cluster.staging.enabled property so files are locked during use. With shared staging, the initial load extracts in the background on one node, but batches can be served from any of the nodes in the cluster, which can improve performance.

When deploying nodes in a cluster to an application server like Tomcat or JBoss, the application server does NOT need any clustering of sessions configured.

It is recommended that SymmetricDS is installed as a standalone service, however there are two other deployment options.

When opening the web console, if there are no nodes defined within the running instance, the Connect Database Wizard will be displayed to guide you through the process of creating one. There are two types of nodes:

A third option will perform the Setup Demo installation, which does the following:

Once the SymmetricDS software is installed, an instance of it is running, and a master node is setup, the synchronization scenario must be configured (i.e. what tables and/or files do I want to synchronize from which source node groups to which target node groups). The Add Table(s) Wizard simplifies this process by walking you through several simple configuration steps.

The Add Table(s) Wizard can be found under the Configure→Overview screen.

Once configuration is complete SymmetricDS will automatically pop up a Connect Database Wizard if there is only one node currently setup in your network.

See Add Node for more information.

The connect database wizard generates a properties file that contains all the information a node needs to bootstrap itself.

Each node that is deployed to a server is represented by a properties file that allows it to connect to a database and register with a parent node. Properties are configured in a file named xxxxx.properties. It is placed in the engines directory of the SymmetricDS install. The file is usually named according to the engine.name, but it is not a requirement.

To give a node its identity, the following properties are required. Any other properties found in conf/symmetric.properties can be overridden for a specific engine in an engine’s properties file. If the properties are changed in conf/symmetric.properties they will take effect across all engines deployed to the server.

See Startup Parameters, for additional parameters that can be specified in the engine properties file.

Load only nodes can be configured for nodes that are only designed to load data into the database. This prevents any triggers or runtime tables from being installed on this database but still allow data to be replicated to it.

There are two ways a SymmetricDS configuration can be imported. Both ways support importing an export that is in CSV format. In order to import in SQL format you would run the SQL script via database specific tools or import through the web console in Configure → Overview.

Export your configuration at any time through the web console. Use the drop down to select the format you would like to use for the export.

Exporting your configuration might be useful in order to save a configuration in source control or to be used as an import into another environment. Export and Import are frequently used to migrate configuration between test and production environments.

In SymmetricDS, configuration rules are applied to groups of nodes versus individual nodes. A group is a categorization of nodes with similar synchronization needs. For example, in a synchronization scenario where a corporate office database is synchronized with field office databases, two node groups would be created, one for the corporate office database (Corporate), and one for the field office databases (Field_office). In the corporate group, there would be a single node and database. In the field_office group, there would be many nodes and databases, one for each field office. Configuration rules/elements are applied to the node group versus the individual nodes in order to simplify the configuration setup (no need to configure each individual field office node, just how the field office nodes sync with the corporate office node).

Group links define at a high level how data moves throughout your synchronization scenario. The group link defines which node groups will synchronize data to other node groups and within that exchange, which node group will initiate the conversation for that exchange.

Routers ride on top of group links. While a group link specifies that data should be moved from nodes in a source node group to nodes in a target node group, routers define more specifically which captured data from a source node should be sent to which specific nodes in a target node group, all within the context of the node group link.

Once group links and routers are defined, configuration must be completed to specify which data (tables, file systems, etc.) should be synchronized over those links and routers. The next step in defining which specific data in the database is moved is to define logical groupings for that data. Channels define those logical groupings. As an example, a set of tables that hold customer data might be logically grouped together in a Customer channel. Sales, returns, tenders, etc. (transaction data) might be logically grouped into a transaction channel. A default channel is automatically created that all tables will fall into unless other channels are created and specified. The default channel is called 'default'.

Channels can be disabled, suspended, or scheduled as needed.

The next step in defining the synchronization scenario is to define which tables should be synchronized. The simplest way to do this is by using the Auto Create…​ button on the Configure → Table Triggers screen. The Auto Create functionality introspects the master node’s database and looks for available tables to synchronize.

Note that you will be configuring tables to synchronize for specific Routers. You will get a chance to select tables for each configured Router. Select the channel you desire from the dropdown, select the tables that should be synchronized using that channel, and then click the Next button. A summary will be presented at the end of the configuration. Click Finish to create the triggers.

The Auto Create functionality can be used repeatedly to select different table, router and channel combinations. If you are configuring a new set of tables triggers that should use an independent Trigger definition be sure to enter values for either the Trigger Prefix or the Trigger Suffix fields. These will be used to create a unique Trigger Id.

For each table selected in the Auto Create wizard, a corresponding Table Trigger configuration element will be added that can be maintained within the Table Triggers list screen. New Table Trigger configuration elements can also be created manually from this screen.

As discussed previously, Routers define more specifically which captured data from a source node should be sent to which specific nodes in a target node group. Table Triggers define which tables should be synchronized. Table Routing defines how the Routers and Table Triggers work together, specifying what tables are associated with each router (and thus the direction the table data flows).

The simplest way to set up Table Routing is to use the Auto Create…​ button.

You can also select routers on the first screen of the auto create if you would like to select routers first then triggers. Both approaches will result in the same table routing.

The table routing elements created by the wizard can be maintained from the Table Routing List Screen. New table routing entries can also be created manually from this screen if desired.

Table groups are used to define collections of tables that will synchronize their data at the same time. When one row from a table in a table group is changed on the source, all corresponding rows from other tables in the same group will also be synchronized to the target.

Table group hierarchies define the tables that belong to a table group and their relationships to each other, with each hierarchy representing a single table. Each table group hierarchy can have a parent, but it is not necessary for every hierarchy to have a parent. It is possible to configure multiple table group hierarchies for a single table if the table has multiple parents.

In addition to supporting database synchronization, SymmetricDS also supports File Synchronization. Similar to database synchronization which allows configuring Table Triggers, SymmetricDS also supports setting up File Triggers. A file trigger is equivalent to specifying a directory structure or path that should be "watched" for files that need to be synchronized.

The file routing concept is identical to the Table Routing concept except that it is for files versus database tables. The File Triggers specify which directory structures on the source node to watch, and the Routers define where the data is sent based on the configured router. Similar to Table Routing the simplest way to set up file routing is via the use of the Auto Create button.

You can also select routers on the first screen of the auto create if you would like to select routers first then file triggers. Both approaches will result in the same file routing.

The file routing elements created by the wizard can be maintained from the File Routing List Screen. New file routing entries can also be created manually from this screen if desired.

Conflict detection is the act of determining if an insert, update or delete is in "conflict" due to the target data row not being consistent with the data at the source prior to the insert/update/delete. Without any overriding configuration, the system uses a detection of USE_CHANGED_DATA and a resolution of NEWER_WINS by default.

Transforms allow you to manipulate data on a source node or target node, as the data is being loaded or extracted.

The source trigger captures data changes that are passed through transformations during extraction from the source and during loading at the target. If any enhancement with additional data is needed, an extract transform can access the source database, while a load transform can access the target database. A single row change may be processed by multiple transforms on the same group link, which transforms it into multiple target rows. Rows for the same target table do not merge, which means multiple transforms with the same target table results in multiple rows for that target table.

Load Filters are a way to take a specific action when a row of data is loaded by SymmetricDS at a destination database node.

Extensions are custom code written to a plug-in interface, which allows them to run inside the engine and change its default behavior. Saving extension code in the configuration has the advantage of dynamically running without deployment or restarting. Configured extensions are available to other nodes and move between environments when configuration is exported and imported.

In SymmetricDS, jobs are tasks that are scheduled to run by a job manager. These jobs do the majority of synchronization work for SymmetricDS. In addition to the built in jobs, you can create custom jobs in Configuration to run for specified node groups.

Note that parameter values will be created for the schedule, in the form of job.<name>.cron OR job.<name>.period.time.ms, depending on if a cron of period of time was entered. If both the cron and period parameters are present, the cron will take precedence.

This is an example BSH job:

This is the same job as a Java job. This might perform a little better, but you’ll need to have a JDK (not just JRE) available on your nodes for this to compile.

This is an example of a SQL job that updates the heartbeat_time of the current node. Available tokens are: :NODE_ID and :NODE_GROUP_ID.

To add your job expression/script navigate to the Configure Jobs page, select your job and click the button "Edit Script". The following editor will appear.

Parameters can be used to help tune and configure your SymmetricDS configuration. Parameters can be set for an individual node or for all nodes in your network.

See Parameter List for a complete list of parameters.

Additional users may be set up to access the SymmetricDS web console.

Configuring a Users authentication on SymmetricDS using LDAP is as simple as setting up the following three Parameters.

A list of base DNs can be specified by separating each entry by a pipe ("|") symbol.
For example:
ou=Users,o=IT,c=US,dc=corp,dc=local|ou=Users,o=Tech,c=US,dc=corp,dc=local

These parameters can be set on the Configure LDAP page by filling out the form and clicking Save.

These parameters can also be set by manually by entering the desired values in Configure→Parameters.

You may test the values that have been input into the form to test the connection to your LDAP directory. To do this, click the Test button, enter the user credentials and click Test to test the authentication. If the authentication succeeded, save the form.

The web console requires a valid license key before it will allow access to screens. The user is prompted automatically to enter a valid license key if one is missing. The license key can also be updated from the Configure License screen.

The license key is a block of encoded text that is sent to the user over email, or it can be retrieved from the Support Center. When an installed license key expires, the web console will require a new valid key before allowing access, but data synchronization and command line access will continue to function normally.

A mail server can be configured for sending email notifications.

The "Test" button will use the current settings on the screen to connect to the mail server with the configured transport and report any errors.

A monitor watches some part of the system for a problem, checking to see if the monitored value exceeds a threshold. (To be notified immediately of new monitor events, configure a notification.)

A notification sends a message to the user when a monitor event records a system problem. First configure a monitor to watch the system and record events with a specific severity level. Then, configure a notification to match the severity level and write to the log or send an email.

Nodes can be added and managed in the Nodes screen under the Manage tab.

Most work done by SymmetricDS is initiated by jobs. Jobs are tasks that are started and scheduled by a job manager. Jobs are enabled by the start.<name>.job parameter.

Most jobs are enabled by default. The frequency at which a job runs is controlled by one of two parameters:

If a valid cron property exists in the configuration, then it will be used to schedule the job. Otherwise, the job manager will attempt to use the period.time.ms property.

From the manage jobs screen the frequency that a job will run for the current node in the cluster can be managed. If you want to change the frequency a job runs across a group or for everyone, you modify the parameter in the Parameters screen.

A job can also be stopped and restarted. If a job is scheduled to run infrequently and the job is needed to run immediately you can select job and click Run Now.

SymmetricDS utilizes Spring’s CRON support, which includes seconds as the first parameter. This differs from the typical Unix-based implementation, where the first parameter is usually minutes. For example, */15 * * * * * means every 15 seconds, not every 15 minutes. See Spring’s documentation for more details.

SymmetricDS installs database triggers to capture changes in the DATA table. A record of the triggers that were installed and what columns are being captured is stored in the TRIGGER_HIST table. When data is captured in DATA it references the TRIGGER_HIST record that represented the trigger at the time data was captured.

This is necessary because if a trigger is rebuilt after columns are added or removed and data that was captured by the old trigger has not yet been delivered, we need a record of what columns were in play at the time the data had been captured.

The Installed Triggers Screen is used to view tables that have successfully been installed with triggers.

This screen allows you to Rebuild an individual database trigger or Rebuild All database triggers. It also allows you to Drop triggers. Only reason you might need to drop triggers to alter a table or perform a batch job where you don’t want data to be captured.

The TRIGGER_HIST table records the reason a trigger was rebuilt. The following reasons are possible:

A configuration entry in Trigger without any history in Trigger Hist results in a new trigger being created (N). The Trigger Hist stores a hash of the underlying table, so any alteration to the table causes the trigger to be rebuilt (S). When the last_update_time is changed on the Trigger entry, the configuration change causes the trigger to be rebuilt ©. If an entry in Trigger Hist is missing the corresponding database trigger, the trigger is created (T).

The Outgoing Loads screen shows the number of outgoing loads that have been queued. It also lists loads that have had Outgoing Batches created. The screen shows loads that are sourced from the current node.

You can cancel a load that is in progress by selecting the load and pressing the Cancel button.

The Incoming Loads screen shows the number of incoming loads that have been queued. It also lists loads that have had Incoming Batches created. The screen shows loads that are targeted at the current node.

You can cancel a load that is in progress by selecting the load and pressing the Cancel button.

The Outgoing Batches screens allows you to monitor data that has been routed.

Outgoing batches are delivered to the target node when the source node pushes or when the target node pulls.

A single push or pull connection is called a synchronization.

For one synchronization, each enabled channel will be processed. Channels are processed in the order defined by the Processing Order setting on the channel with two exceptions:

When outgoing batches are selected for a node and a channel, the maximum number of batches that are extracted per synchronization is controlled by the Max Batch To Send setting on the channel.

There is also a setting that controls the max number of bytes to send in one synchronization. If SymmetricDS has extracted more than the number of bytes configured by the transport.max.bytes.to.sync parameter, then it will finish extracting the current batch and then finish synchronization so the client has a chance to process and acknowledge the "big" batch. This may happen before the configured Max Batch To Send has been reached.

When extracting a batch, data is first extracted to the Staging Area and then sent across the network from the Staging Area. The staging area is used to minimize the amount of time a database connection is being used when streaming over slower networks. The use of the staging area can be turned off by setting the stream.to.file.enabled parameter.

The Incoming Batches screens allows you to monitor batches that have been delivered to the target node.

Incoming batches are delivered to the target node when the source node pushes or when the target node pulls.

Incoming batches are written to the Staging Area first and then loaded. The use of the staging area can be turned off by setting the stream.to.file.enabled parameter.

SymmetricDS creates temporary extraction and data load files with the CSV payload of a synchronization when the value of the stream.to.file.threshold.bytes SymmetricDS property has been reached. Before reaching the threshold, files are streamed to/from memory. The default threshold value is 0 bytes. This feature may be turned off by setting the stream.to.file.enabled property to false.

SymmetricDS creates these temporary files in the directory specified by the java.io.tmpdir Java System property.

The location of the temporary directory may be changed by setting the Java System property passed into the Java program at startup. For example,

The Staging Area screen shows files that are currently in the staging area. Staging area can be cleared at any time by clicking the Clear Staging button.

The Processes screen shows what is actively going on in SymmetricDS for the current node.

Both the Pull Job and the File Sync Pull Job can be configured to pull multiple nodes in parallel. In order to take advantage of this the pull.thread.per.server.count or file.pull.thread.per.server.count should be adjusted (from the default value of 1) to the number to the number of concurrent pulls you want to occur per period on each SymmetricDS instance.

This screen shows pull activity for both table and file synchronization.

Pull activity is recorded in the NODE_COMMUNICATION table. This table is also used as a semaphore to lock pull activity across multiple servers in a cluster.

Both the Push Job and the File Sync Push Job can be configured to push multiple nodes in parallel. In order to take advantage of this the push.thread.per.server.count or file.push.thread.per.server.count should be adjusted (from the default value of 1) to the number to the number of concurrent pushes you want to occur per period on each SymmetricDS instance.

This screen shows pull activity for both table and file synchronization.

Push activity is recorded in the NODE_COMMUNICATION table. This table is also used as a semaphore to lock push activity across multiple servers in a cluster.

The JVM Properties screen is a convenience screen that shows JVM System Properties.

The JVM Threads Screen shows active threads in the JVM.

The Monitors screen allows you to view events of system problems recorded by both local and remote nodes. The list of events can be filtered to limit the number of events displayed, event type, severity level, and node ID. Filtering by severity level will match the level you choose and any level above it. Events are listed in descending order by event time, but the order can be changed by clicking column headings. The remove button will clear the event from the table on the current node. Events are purged automatically each night using the purge.retention.minutes parameter to remove by event time.

When a Monitor is configured, it is run periodically to check the current value of a system metric and compare it to a threshold value. Different monitor types can check the CPU usage, disk usage, memory usage, batch errors, outstanding batches, unrouted data, number of data gaps, and job errors. Custom monitor types can be created using Extensions that use the IMonitorType interface. When the value returned from the check meets or exceeds the threshold value, a MONITOR_EVENT is recorded. The MONITOR_EVENT table is synchronized on the "monitor" channel, which allows a central server to see events from remote nodes, but this behavior can be disabled by setting the monitor.events.capture.enabled parameter to false.

To be immediately notified of a monitor event, use Notifications to match on the severity level. Different notification type can send a message by writing to the log or sending an email. Custom notification types can be created using Extensions that use the INotificationType interface. In order to send email, the Mail Server should be configured.

The Security panel manages the SSL/TLS certificates and keys.

Rest API keys must be set up in order to access the REST API. Attempting to access the REST API without a key will result in HTTP error code 403 (forbidden). When a new key is created, it will only be displayed once, so be sure to copy it and save it for future use.

The following is an example of how to include the key in a curl command:

A user interface for the REST API is available on the Help → REST API screen. When the screen is first visited, the padlock icons are open to indicate that a REST API key is not being used. To enter the key, click the Authorize button, which is highlighted in red in the below image. After entering the key, the padlocks will close.

The standalone SymmetricDS installation uses Log4J for logging. The configuration file is conf/log4j.xml. The log4j.xml file has hints as to what logging can be enabled for useful, finer-grained logging.

There is a command line option to turn on preconfigured debugging levels. When the --debug option is used the conf/debug-log4j.xml is used instead of log4j.xml.

SymmetricDS proxies all of its logging through SLF4J. When deploying to an application server or if Log4J is not being leveraged, then the general rules for SLF4J logging apply.

You can use the logging screen to dynamically adjust the log level in order to help triage issues. When developing transforms it is useful to turn on Log Sync Details.

The db.user and db.password properties can be protected by encrypting them. This encryption can be done two different ways.

The first option is to pass the text as an argument:

The second option is without an argument, and it will prompt you to enter text:

Encrypted text starts with "enc:" to differentiate it from plain text. See the Keystores section for an explanation of the encryption key.

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:

Monitoring and administrative operations can be performed using Java Management Extensions (JMX). SymmetricDS exposes JMX attributes and operations that can be accessed from the jmx command, Java’s jconsole, or a third party tool.

In order to use jconsole, you must enable JMX remote management in the JVM. You can edit the startup scripts to set the following system parameters.

More details about enabling JMX for JConsole can be found here.

Using the Java jconsole command, SymmetricDS is listed as a local process named SymmetricLauncher. In jconsole, SymmetricDS appears under the MBeans tab under the name defined by the engine.name property. The default value is SymmetricDS.

The management interfaces under SymmetricDS are organized as follows:

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.

The XmlPublisherDatabaseWriterFilter is a IDatabaseWriterFilter that may be configured to publish specific tables as an XML message to a JMS provider. See Extensions 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.

The following is an example extension point configuration that will publish four tables in XML with a root tag of 'sale'. Each XML message will be grouped by the batch and the column names identified by the groupByColumnNames property which have the same values.

The publisher property on the XmlPublisherDatabaseWriterFilter takes an interface of type IPublisher. The implementation demonstrated here is an implementation that publishes to JMS using Spring’s JMS template. 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.

The above configuration will publish XML similar to the following:

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 router_type of a ROUTER to the Spring bean name of the registered extension point. Of course, the router would need to be linked through TRIGGER_ROUTERs to each TRIGGER table that needs published.

SymmetricDS not only supports the synchronization of database tables, but it also supports the synchronization of files and folders from one node to another.

Variables can be used throughout configuration with the $(variableName) syntax. Check the documentation for each configuration item to see which variables it supports. A substring of the variable value can be specified with a starting index and an optional ending index. The first character is at index 0, and the end index is not included in the substring. Therefore, the length of the substring will be end index minus start index.

Examples when $(externalId) is set to 00001-002:

The variable value can be formatted using a format string supported by java.lang.String.format().

Examples when $(externalId) is set to 1:

There are a number of display settings available for the web console. They are accessible by clicking the cog icon in the top right corner of the screen and navigating to the "Display" tab of the settings dialog. These settings apply to the console user that is currently logged in.

SymmetricDS has a pluggable architecture that can be extended. A Java class that implements the appropriate extension point interface, can implement custom logic and change the behavior of SymmetricDS to suit special needs. All supported extension points extend the IExtensionPoint interface. The available extension points are documented in the following sections.

When SymmetricDS starts up, the ExtensionPointManager searches a Spring Framework context for classes that implement the IExtensionPoint interface, then creates and registers the class with the appropriate SymmetricDS component.

Extensions should be configured in the conf/symmetric-extensions.xml file as Spring beans. The jar file that contains the extension should be placed in the web/WEB-INF/lib directory.

If an extension point needs access to SymmetricDS services or needs to connect to the database it may implement the ISymmetricEngineAware interface in order to get a handle to the ISymmetricEngine.

The INodeGroupExtensionPoint interface may be optionally implemented to indicate that a registered extension point should only be registered with specific node groups.

SymmetricDS has its web-enabled, fault-tolerant, database synchronization software available on the Android mobile computing platform. The Android client follows all of the same concepts and brings to Android all of the same core SymmetricDS features as the full-featured, Java-based SymmetricDS client. The Android client is a little bit different in that it is not a stand-alone application, but is designed to be referenced as a library to run in-process with an Android application requiring synchronization for its SQLite database.

By using SymmetricDS, mobile application development is simplified, in that the mobile application developer can now focus solely on interacting with their local SQLite database. SymmetricDS takes care of capturing and moving data changes to and from a centralized database when the network is available

The same core libraries that are used for the SymmetricDS server are also used for Android. SymmetricDS’s overall footprint is reduced by eliminating a number of external dependencies in order to fit better on an Android device. The database access layer is abstracted so that the Android specific database access layer could be used. This allows SymmetricDS to be efficient in accessing the SQLite database on the Android device.

In order to convey how to use the SymmetricDS Android libraries, the example below will show how to integrate an Android application with the Quick-Start demo configuration. This Android application will create an embedded SQLite database, all SymmetricDS run-time tables, and configure the Quick-Start demo tables (ITEM, ITEM_SELLING_PRICE, SALE_TRANSACTION, SALE_RETURN_LINE_ITEM) for synchronization. The application has a basic user interface that can run queries on the SQLite database to demonstrate synchronization with a Quick-Start demo corp server.

Android Studio 3.0.1 and Android SDK 26 were used for this example. The example Android application can be cloned into Android Studio using the GitHub project located here: https://github.com/JumpMind/symmetric-android-client-demo

SymmetricDS for Android comes as a zip file of Java archives (jar files) that are required by the SymmetricDS client at runtime. The libs directory containing the necessary .jar files can be downloaded as a zip archive (symmetric-android-VERSION.zip) from the SymmetricDS downloads page. Alternatively, the libs directory can be generated by cloning the symmetric-ds GitHub repository and running the following command in the symmetric-assemble directory:

The first step to using SymmetricDS in an Android application is to unzip the jar files into a location where the project will recognize them. The latest Android SDK requires that these jar files be put into a libs directory under the app directory of the Android application project.