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From "Timothy Bish (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AMQ-6099) Allow broker to read any OpenWire version from KahaDB
Date Tue, 22 Dec 2015 15:46:46 GMT

    [ https://issues.apache.org/jira/browse/AMQ-6099?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15068284#comment-15068284
] 

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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