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https://issues.apache.org/jira/browse/AMQ-5748?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14517981#comment-14517981
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Timothy Bish commented on AMQ-5748:
-----------------------------------
Have a look at StoredDestinationMarshaller in MessageDatabase.java (1909) for
some insights into handling version updates.
> Add the ability to get Message Size from a Message Store
> --------------------------------------------------------
>
> Key: AMQ-5748
> URL: https://issues.apache.org/jira/browse/AMQ-5748
> Project: ActiveMQ
> Issue Type: New Feature
> Components: Broker
> Affects Versions: 5.11.1
> Reporter: Christopher L. Shannon
> Priority: Minor
>
> Currently, the {{MessageStore}} interface supports getting a count for
> messages ready to deliver using the {{getMessageCount}} method. It would
> also be very useful to be able to retrieve the message sizes for those counts
> as well for keeping track of metrics.
> I've created a pull request to address this that adds a {{getMessageSize}}
> method that focuses specifically on KahaDB and the Memory store. The KahaDB
> store uses the same strategy as the existing {{getMessageCount}} method,
> which is to iterate over the index and total up the size of the messages.
> There are unit tests to show the size calculation and a unit test that shows
> a store based on version 5 working with the new version (the index is rebuilt)
> One extra issue is that the size was not being serialized to the index (it
> was not included in the marshaller) so that required making a slight change
> and adding a new marshaller for {{Location}} to store the size in the
> location index of the store. Without this change, the size computation would
> not work when the broker was restarted since the size was not serialized.
> Note that I wasn't sure the best way to handle the new marshaller and version
> compatibilities so I incremented the KahaDB version from 5 to 6. If an old
> version of the index is loaded, the index should be detected as corrupted and
> be rebuilt with the new format. If there is a better way to handle this
> upgrade let me know and the patch can certainly be updated.
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