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https://issues.apache.org/jira/browse/AMQ-6099?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15068284#comment-15068284
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Timothy Bish commented on AMQ-6099:
-----------------------------------
Two things that make this difficult. First people who treat the broker like a
database tend to have messages hoarded in the store for indeterminately long
amounts of time. Second, the OpenWire marshallers aren't designed to attempt
to read unknown versions blobs and can easily get you into a scenario where one
might misread a size marker and run you OOM when trying to allocate buffers.
> Allow broker to read any OpenWire version from KahaDB
> -----------------------------------------------------
>
> Key: AMQ-6099
> URL: https://issues.apache.org/jira/browse/AMQ-6099
> Project: ActiveMQ
> Issue Type: New Feature
> Components: KahaDB
> Affects Versions: 5.x
> Reporter: Tim Bain
>
> The current KahaDB implementation only allows a single OpenWire version to be
> read from the store. This works fine during normal operations, but when a
> user upgrades to a version of ActiveMQ that uses a different OpenWire
> version, the new broker is unable to read any persisted messages from the
> store because of the version mismatch, as described in AMQ-5995.
> Broker upgrades are going to happen, and the requirement that they be done
> with an empty message store, or that the user apply temporary workarounds
> like running the old broker in a networked configuration that's not the
> standard config for the cluster, leads to a less-than-satisfactory experience
> during the upgrade. As much as possible, broker upgrades should be seamless;
> sometimes that's not possible, but in this case it seems like code that would
> be able to read any version of OpenWire but only write the current one (and
> that could be less-efficient with older versions if necessary) wouldn't be
> all that hard and would eliminate this problem.
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