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Available as of Fuse Mediation Router 2.3

HawtDB is a very lightweight and embedable key value database. It allows together with Fuse Mediation Router to provide persistent support for various Fuse Mediation Router features such as Aggregator in Implementing Routes.

Current features it provides:

  • HawtDBAggregationRepository

HawtDBAggregationRepository is an AggregationRepository which on the fly persists the aggregated messages. This ensures that you will not loose messages, as the default aggregator will use an in memory only AggregationRepository.

It has the following options:

Option Type Description
repositoryName String A mandatory repository name. Allows you to use a shared HawtDBFile for multiple repositories.
persistentFileName String Filename for the persistent storage. If no file exists on startup a new file is created.
bufferSize int The size of the memory segment buffer which is mapped to the file store. By default its 8mb. The value is in bytes.
sync boolean Whether or not the HawtDBFile should sync on write or not. Default is true. By sync on write ensures that its always waiting for all writes to be spooled to disk and thus will not loose updates. If you disable this option, then HawtDB will auto sync when it has batched up a number of writes.
pageSize short The size of memory pages. By default its 512 bytes. The value is in bytes.
hawtDBFile HawtDBFile Use an existing configured org.apache.camel.component.hawtdb.HawtDBFile instance.
returnOldExchange boolean Whether the get operation should return the old existing Exchange if any existed. By default this option is false to optimize as we do not need the old exchange when aggregating.
useRecovery boolean Whether or not recovery is enabled. This option is by default true. When enabled the Fuse Mediation Router Aggregator in Implementing Routes automatic recover failed aggregated exchange and have them resubmitted.
recoveryInterval long If recovery is enabled then a background task is run every x'th time to scan for failed exchanges to recover and resubmit. By default this interval is 5000 millis.
maximumRedeliveries int Allows you to limit the maximum number of redelivery attempts for a recovered exchange. If enabled then the Exchange will be moved to the dead letter channel if all redelivery attempts failed. By default this option is disabled. If this option is used then the deadLetterUri option must also be provided.
deadLetterUri String An endpoint uri for a Dead Letter Channel in Implementing Routes where exhausted recovered Exchanges will be moved. If this option is used then the maximumRedeliveries option must also be provided.

The repositoryName option must be provided. Then either the persistentFileName or the hawtDBFile must be provided.

The HawtDBAggregationRepository will by default recover any failed Exchange. It does this by having a background tasks that scans for failed Exchanges in the persistent store. You can use the checkInterval option to set how often this task runs. The recovery works as transactional which ensures that Fuse Mediation Router will try to recover and redeliver the failed Exchange. Any Exchange which was found to be recovered will be restored from the persistent store and resubmitted and send out again.

The following headers is set when an Exchange is being recovered/redelivered:

Header Type Description
Exchange.REDELIVERED Boolean Is set to true to indicate the Exchange is being redelivered.
Exchange.REDELIVERY_COUNTER Integer The redelivery attempt, starting from 1.

Only when an Exchange has been successfully processed it will be marked as complete which happens when the confirm method is invoked on the AggregationRepository. This means if the same Exchange fails again it will be kept retried until it success.

You can use option maximumRedeliveries to limit the maximum number of redelivery attempts for a given recovered Exchange. You must also set the deadLetterUri option so Fuse Mediation Router knows where to send the Exchange when the maximumRedeliveries was hit.

You can see some examples in the unit tests of camel-hawtdb, for example this test.

To use HawtDB in your Fuse Mediation Router routes you need to add the a dependency on camel-hawtdb.

If you use maven you could just add the following to your pom.xml, substituting the version number for the latest & greatest release (see the download page for the latest versions).

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-hawtdb</artifactId>
  <version>2.3.0</version>
</dependency>

See Also:

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