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From "ASF subversion and git services (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (QPID-4348) HA Use independent sequence numbers for identifying messages.
Date Mon, 17 Jun 2013 14:19:20 GMT

    [ https://issues.apache.org/jira/browse/QPID-4348?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13685599#comment-13685599
] 

ASF subversion and git services commented on QPID-4348:
-------------------------------------------------------

Commit 1493771 from [~aconway]
[ https://svn.apache.org/r1493771 ]

QPID-4348: HA Use independent sequence numbers for identifying messages

Previously HA code used queue sequence numbers to identify messasges.
This assumes that message sequence is identical on primary and backup.

Implementing new features (for example transactions) requires that we tolerate
ordering differences between primary and backups.

This patch introduces a new, queue-scoped HA sequence number managed by the HA
plugin.  The HA ID is set *before* the message is enqueued and assigned a queue
sequence number. This means it is possible to identify messages before they are
enqueued, e.g. messages in an open transaction.
                
> HA Use independent sequence numbers for identifying messages.
> -------------------------------------------------------------
>
>                 Key: QPID-4348
>                 URL: https://issues.apache.org/jira/browse/QPID-4348
>             Project: Qpid
>          Issue Type: Improvement
>          Components: C++ Clustering
>    Affects Versions: 0.18
>            Reporter: Alan Conway
>            Assignee: Alan Conway
>
> Currently HA code uses queue sequence numbers to identify messasges.
> This assumes that message sequence is identical on primary and backup.
> Implementing new features (for example transactions) requires that we tolerate
> ordering differences between primary and backups.
> We introduces a new, queue-scoped HA sequence number managed by the HA plugin.
> This is used to identify messages independently of queue sequence numbers.
> Needs careful implementation to avoid bad performance effects.
> - Avoid adding headers, use the same mechansim as we have now for sending HA seq. nos.
> - Use an efficient index struct (e.g. dequeue) to map HA seq. to queue seq.
> The benefits:
> - required to support TX
> - required for re-use of stored messages for catchup
> - more robust - does not require primary and backups to have identical message ordering
on their queues.

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