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From "James Strachan (JIRA)" <j...@apache.org>
Subject [jira] Resolved: (CAMEL-125) Support for a stream-processing resequencer.
Date Tue, 28 Aug 2007 11:08:22 GMT

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

James Strachan resolved CAMEL-125.
----------------------------------

       Resolution: Fixed
    Fix Version/s: 1.2.0

Patch applied with huge thanks - great work Martin!

One thought I had was, should we make the ResequenceEngine take a Processor type thing to
deliver messages rather than using the Queue and SequenceSender. I guess we could reuse a
SedaProcessor or something; I did wonder if we might want to support synchronous dispatch
of the messages for easier transaction handling. 

e.g. in one JMS session say, consume a bunch of messages and send them on in the right order
- in a single thread & JMS transaction.

> 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
>             Fix For: 1.2.0
>
>         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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