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| author | Alan Conway <aconway@apache.org> | 2012-09-17 18:37:41 +0000 |
|---|---|---|
| committer | Alan Conway <aconway@apache.org> | 2012-09-17 18:37:41 +0000 |
| commit | fe05b47cbad4e580cc3e00dcc42c0d46084e3ed0 (patch) | |
| tree | c76147b6c0bfca6756511901427a18ef846d47ab | |
| parent | 0aeb3a188445e03e1a99354874e900bbeefc865c (diff) | |
| download | qpid-python-fe05b47cbad4e580cc3e00dcc42c0d46084e3ed0.tar.gz | |
NO-JIRA: HA improve documentation of role of sender capacity in failover.
git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1386764 13f79535-47bb-0310-9956-ffa450edef68
| -rw-r--r-- | qpid/doc/book/src/cpp-broker/Active-Passive-Cluster.xml | 37 |
1 files changed, 26 insertions, 11 deletions
diff --git a/qpid/doc/book/src/cpp-broker/Active-Passive-Cluster.xml b/qpid/doc/book/src/cpp-broker/Active-Passive-Cluster.xml index 805ceb06e0..9617a843ed 100644 --- a/qpid/doc/book/src/cpp-broker/Active-Passive-Cluster.xml +++ b/qpid/doc/book/src/cpp-broker/Active-Passive-Cluster.xml @@ -55,30 +55,45 @@ under the License. <title>Avoiding message loss</title> <para> In order to avoid message loss, the primary broker <emphasis>delays - acknowledgment</emphasis> of messages received from clients until the - message has been replicated to and acknowledged by all of the back-up + acknowledgment</emphasis> of messages received from clients until the message has + been replicated to and acknowledged by all of the back-up brokers. This means that + all <emphasis>acknowledged</emphasis> messages are safely stored on all the backup brokers. </para> <para> - Clients buffer unacknowledged messages and re-send them in the event of - a fail-over. + Clients keep <emphasis>unacknowledged</emphasis> messages in a buffer + <footnote> + <para> + You can control the maximum number of messages in the buffer by setting the + client's <literal>capacity</literal>. For details of how to set the capacity + in client code see "Using the Qpid Messaging API" in + <citetitle>Programming in Apache Qpid</citetitle>. + </para> + </footnote> + until they are acknowledged by the primary. If the primary fails, clients will + fail-over to the new primary and <emphasis>re-send</emphasis> all their + unacknowledged messages. <footnote> <para> Clients must use "at-least-once" reliability to enable re-send of unacknowledged messages. This is the default behavior, no options need be set to enable it. For details of client addressing options see "Using the Qpid Messaging API" - in <citetitle>Programming in Apache Qpid</citetitle> + in <citetitle>Programming in Apache Qpid</citetitle>. </para> </footnote> - If the primary crashes before a message is replicated to - all the backups, the client will re-send the message when it fails over - to the new primary. + <para> + So if the primary crashes, all the <emphasis>acknowledged</emphasis> messages will + be available on the backup that takes over as the new primary. The + <emphasis>unacknowledged</emphasis> messages will be re-sent by the clients. Thus + no messages are lost. + </para> </para> <para> Note that this means it is possible for messages to be - <emphasis>duplicated</emphasis>. In the event of a failure it is - possible for a message to be both received by the backup that becomes - the new primary <emphasis>and</emphasis> re-sent by the client. + <emphasis>duplicated</emphasis>. In the event of a failure it is possible for a + message to received by the backup that becomes the new primary + <emphasis>and</emphasis> re-sent by the client. The application must take steps + to identify and eliminate duplicates. </para> <para> When a new primary is promoted after a fail-over it is initially in |