[jira] Commented: (CAMEL-125) Support for a stream-processing resequencer.

["James Strachan (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/activemq/browse/CAMEL-125?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_40008 ] 

James Strachan commented on CAMEL-125:
--------------------------------------

Awesome patch and comments! Am on vacation today but will hopefully get chance to review fully and commit on tueday. 

Incidentally yes I'd love to combine camel and servicemix-eip together - contributions most welcome. In ServiceMix 4 it'd be great to combine them into Camel and have ServiceMix natively understand Camel components maybe (FWIW the Camel API is extremely close to the new ServiceMix 4 APIs). Contributions always welcome! Keep up the great work Martin!

> Support for a stream-processing resequencer.
> --------------------------------------------
>
>                 Key: CAMEL-125
>                 URL: https://issues.apache.org/activemq/browse/CAMEL-125
>             Project: Apache Camel
>          Issue Type: Improvement
>          Components: camel-core, camel-spring
>    Affects Versions: 1.1.0
>         Environment: Java 6, Windows XP
>            Reporter: Martin Krasser
>         Attachments: camel-core-patch.txt, camel-spring-patch.txt
>
>
> Attached is a patch that adds a stream-processing resequencer to Camel. The resequencing algorithm is based on the detection of gaps in a message stream rather than on a fixed batch size. Gap detection in combination with timeouts removes the constraint of having to know the number of messages of a sequence in advance (although a capacity parameter prevents the resequencer from running out of memory) 
> Route builder examples for the stream-processing resequencer:
> {{from("direct:start").resequencer(header("seqnum")).stream().to("mock:result")}}
> is equivalent to:
> {{from("direct:start").resequencer(header("seqnum")).stream(StreamResequencerConfig.getDefault()).to("mock:result")}}
> Custom values for the resequencer's capacity and timeout can be set like in this example:
> {{from("direct:start").resequencer(header("seqnum")).stream(new StreamResequencerConfig(300, 4000L)).to("mock:result")}}
> The XML configuration looks like:
> {code:xml}
> <camelContext id="camel" xmlns="http://activemq.apache.org/camel/schema/spring">
>   <route>
>     <from uri="direct:start"/>
>     <resequencer>
>       <simple>in.header.seqnum</simple>
>       <to uri="mock:result" />
>       <stream-config capacity="300", timeout="4000"/>
>     </resequencer>
>   </route>
> </camelContext>
> {code}
> The existing batch-processing resequencer can be defined as usual:
> {{from("direct:start").resequencer(header("seqnum")).to("mock:result")}}
> which is now equivalent to 
> {{from("direct:start").resequencer(header("seqnum")).batch().to("mock:result")}}
> It is now also possible to define a custom configuration for the existing batch-processing resequencer:  
> {{from("direct:start").resequencer(header("seqnum")).batch(new BatchResequencerConfig(300, 4000L)).to("mock:result")}}
> This set the batchSize to 300 and the batchTimeout to 4000 ms. 
> For the stream-processing resequencer to work, messages must contain a sequence number for which a predecessor and a successor is known. For example a message with the sequence number 3 has a predecessor message with the sequence number 2 and a successor message with the sequence number 4. The message sequence 2,3,5 has a gap because the sucessor of 3 is missing. The resequencer therefore has to retain message 5 until message 4 arrives (or a timeout occurs). 
> Gap detection is done with strategies that implement the SequenceNumberComparator<E> interface. In addition to the java.util.Comparator<E>.compare(E, E) operation the SequenceNumberComparator<E> interface defines the predecessor(E, E) and successor(E, E) operations. The stream resequencer can be configured with cutstom SequenceNumberComparator<E> strategies.
> The stream-processing resequencer uses the same algorithm as the one in ServiceMix-3.2-SNAPSHOT (servicemix-eip). In order to avoid compile-time dependencies to ServiceMix I've copied the ServiceMix-independent resequencing engine over to Camel. This redundancy should be removed once Camel and servicemix-eip are going to be combined (are they?). I can contribute to this task, if needed.

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