I HA: can a master State Unknown to transition to instead of throwing IRE?

Hello

I 5.0.48

I runs tests using the example of quotes with a cluster of four nodes. I have a question about the behavior of the cluster as replicas are killed.

I start with four nodes, n1, n2, n3 and n4. N1 was elected master. N2 - n4 become replicas.

If I kill n3 n1 rest master and written is still allowed as there are sufficient replicas to satisfy policy SIMPLE_MAJORITY. If I didn't then go on to kill n4, n1 is always master but InsufficientReplicasException is thrown in response to each entry. I see in the documentation, it's expected behaviour.

In our case, we want to know immediately when the number of replicas becomes too few to meet the ReplicaAckPolicy, rather than waiting for the next transaction due to InsufficientReplicasException. We wonder if there is a way to organize for the master to the transition from unknown back when this condition arises. If this is not possible, is it possible for the application to learn it in the other direction? I read on Monitor.startListener () and MonitorChangeListener. These could help us?

Any advice would be much appreciated.

Best regards, Keith Wall.

Keith,

Yes, the various mechanisms of notification that informs the user of the status of the members are the right way to go. You have already noticed the Monitor and MonitorChangeListener classes and I hope that the javadoc (starting with com.sleepycat.je.rep.monitor.monitor) chapter in the guide of replication is pretty informative: http://docs.oracle.com/cd/E17277_02/html/ReplicationGuide/monitors.html. Also note the chapter on the use of com.sleepycat.je.rep.StateChangeListener: http://docs.oracle.com/cd/E17277_02/html/ReplicationGuide/replicawrites.html.

The two mechanisms differ from the point of view of the question of if the management is at the point when the application has access to a ReplicatedEnvironment, or if it is done by an entity of the third party, such as a load balancer. They are two sides of the same coin. But neither to totally exempt the application code to handle the possibility of an InsufficientReplicasException.
-It is always possible that the notifications will be sent and processed later than the exception
-l' lack of response to a replica may be due to a temporary network problem, and as it was not a real change state, no notification is sent
-If a node goes down, it cannot send its own notification, of course, and it may take a little while for other nodes to intervene, to detect status change and make a notification

So the notification mechanisms can optimize and reduce the possibility of obtaining an InsufficientReplicasException, but it can not remove it completely. This could lead to having to manage various exceptions in the application code. For a long time, Jeff Alexander wrote this example of how he made a wrapper of the transaction to modularize all exception management: https://blogs.oracle.com/jhalex/entry/handling_transactions_in_bdb_je. We tend to do something in this sense when write us code that emits data against a BDB I HA cluster operations.

Hope that helps,

Linda

Tags: Database

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