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https://issues.apache.org/jira/browse/DERBY-3527?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12583622#action_12583622
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Øystein Grøvlen commented on DERBY-3527:
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Thanks, Jørgen. I think the changes on the master side looks good.
I am still trying to understand the issues around synchronization in
ReplicationMessageReceive.
I wonder whether the following scenario could occur: isConnectedToMaster is
called. Thread notifies ping thread which sends ping, but when it is to get the
receivePongSemaphore, it has already been acquired by readMessage which reads
the pong and calls notify before the isConnectedToMaster has started to wait. I
think this could lead to a false conclusion that the master is down.
> The slave will not notice that a network cable is unplugged and will
> therefore reject failover/stopSlave commands
> -----------------------------------------------------------------------------------------------------------------
>
> Key: DERBY-3527
> URL: https://issues.apache.org/jira/browse/DERBY-3527
> Project: Derby
> Issue Type: Bug
> Components: Replication
> Affects Versions: 10.4.0.0, 10.5.0.0
> Reporter: Jørgen Løland
> Assignee: Jørgen Løland
> Attachments: derby-3527-1a.diff, derby-3527-1a.stat,
> derby-3527-1b.diff, derby-3527-1b.stat, derby-3527-1c.diff, derby-3527-1c.stat
>
>
> If a network cable between the master and slave is unplugged (or a switch
> crashes etc), ObjectInputStream#readObject will not get an exception. Neither
> the socket nor the input stream can be queried for information on whether or
> not the connection is working. AFAIK, the only way to find out if the network
> is down is to send a message.
> The slave commands stopSlave and failover are rejected if the network
> connection is working. To be absolutely sure that the connection is working,
> we need to ping the master when these commands are requested.
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