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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-2921) Replication: Add a network service that connects the master and slave Derby instances
Date Fri, 17 Aug 2007 15:32:31 GMT

    [ https://issues.apache.org/jira/browse/DERBY-2921?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12520588
] 

Rick Hillegas commented on DERBY-2921:
--------------------------------------

Øystein> If I understand correctly, hard-coding the SerialVersionUUID, will mean that
when one later change the serialization form, one will have to manually update the SerialVersionUUID.

If I were coding this myself, my instinct would be to use Externalizable rather than Serializable.
As its very first task, writeExternal() would stamp a version id on the serialization stream.
Symmetrically, as its very first task, readExternal() would read the stamped version id--and
switch based on the actual version id. I find this approach is very flexible. And you are
right, the version id has to change when the serialized form is altered--regardless of whether
the solution is programmed using Serializable or Externalizable.

Øystein> Would not that imply that as long as the format of the message does not change,
running different versions of the master and the slave will work?

I'm not following you. How would you handle the problem described in my comment on August
8: The master hard-uprades and the transactional work done as part of hard upgrade is replayed
into the down-rev slave database. Now the slave database thinks that it is at a higher rev
than the actual Derby code on the slave machine. What will happen if you have to failover
to this inconsistent slave?



> Replication: Add a network service that connects the master and slave Derby instances
> -------------------------------------------------------------------------------------
>
>                 Key: DERBY-2921
>                 URL: https://issues.apache.org/jira/browse/DERBY-2921
>             Project: Derby
>          Issue Type: Sub-task
>          Components: Services
>    Affects Versions: 10.4.0.0
>            Reporter: Jørgen Løland
>            Assignee: V.Narayanan
>         Attachments: Replication_Network_v1.diff, Replication_Network_v1.stat
>
>
> A network connection is required between the master and slave Derby instances of a replicated
database. The connection will be used to send many kinds of messages, including:
> * log records
> * the database (when replication is started)
> * master -> slave commands (like "stop replication")

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