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https://issues.apache.org/jira/browse/DERBY-3254?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12558198#action_12558198
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V.Narayanan commented on DERBY-3254:
------------------------------------
Before starting to make the patch there are a few things I thought I should
detail out
I had earlier decided on the following set of steps to implement failover
* The failover command is given to the master.
* The master flushes the log buffer
* The master sends this command to the slave and waits for a response
* The slave responds with an acknowledgement
* The master stops replication
There are a few refinements to these steps that would become necessary because
of the
following issues
1) When the master stops replication is it necessary for it to shutdown the
database?
I believe the answer is YES because there is no point in having the master
serving clients
when the slave is doing likewise for the same database. Having two databases
serving clients
would create trouble for the users.
2) In the aforementioned steps there is a window between the stop master
operation
(not shutting down database), sending a failover command to the slave, not
succeeding,
restarting master operation.
Stopping master, flushes the log buffer, and stops the log buffer from
buffering more records.
But this does not stop the clients being served. So the next time you start
replication you
would be inconsistent.
Therefore we would need to stop clients in some way before flushing the log
buffer.
The above two issues lead to the following refinements in the steps mentioned
earlier
* The failover command is given to the master
* We stop the clients upon receiving this command
* The master Flushes the log buffer
* The master sends the failover command to the slave and waits for
a response
* The slave responds with a acknowledgement
* The master stops replication and shuts down the database.
In the event of a failure the master would resume serving clients.
> Implement the replication failover functionality
> ------------------------------------------------
>
> Key: DERBY-3254
> URL: https://issues.apache.org/jira/browse/DERBY-3254
> Project: Derby
> Issue Type: Sub-task
> Components: Replication
> Reporter: V.Narayanan
> Assignee: V.Narayanan
> Attachments: failover_impl_notforcommit.diff,
> failover_impl_notforcommit.stat, failover_impl_v1.diff, failover_impl_v1.stat
>
>
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