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https://issues.apache.org/jira/browse/CASSANDRA-13289?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15946991#comment-15946991
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Jason Brown commented on CASSANDRA-13289:
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bq. There is a part of me that doesn't like having a null field
Maybe set the type of the field to {{Optional<AtomicInteger>}}, and set it to
{{Optional.empty}} when not being used? Not sure I love this but it does avoid
an NPE.
bq. I don't want to throw an error at the request level. I can't validate the
configuration. And I don't want to silently not increment the counters.
I agree with these points, especially the last. I suspect not counting would be
confusing to an operator who went out of their way to enable this feature, and
are expecting an output of some kind. I don't think logging is necessary (or
helpful).
wrt timeouts, you are correct. I think I was forgetting that this patch is only
affecting the write path, and I must have been thinking the read path was
pulled along, as well. Either way, this concern is not a real issue.
I'll rereview the ticket now with these things in mind.
> Make it possible to monitor an ideal consistency level separate from actual
> consistency level
> ---------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-13289
> URL: https://issues.apache.org/jira/browse/CASSANDRA-13289
> Project: Cassandra
> Issue Type: New Feature
> Components: Core
> Reporter: Ariel Weisberg
> Assignee: Ariel Weisberg
> Fix For: 4.0
>
>
> As an operator there are several issues related to multi-datacenter
> replication and consistency you may want to have more information on from
> your production database.
> For instance. If your application writes at LOCAL_QUORUM how often are those
> writes failing to achieve EACH_QUORUM at other data centers. If you failed
> your application over to one of those data centers roughly how inconsistent
> might it be given the number of writes that didn't propagate since the last
> incremental repair?
> You might also want to know roughly what the latency of writes would be if
> you switched to a different consistency level. For instance you are writing
> at LOCAL_QUORUM and want to know what would happen if you switched to
> EACH_QUORUM.
> The proposed change is to allow an ideal_consistency_level to be specified in
> cassandra.yaml as well as get/set via JMX. If no ideal consistency level is
> specified no additional tracking is done.
> if an ideal consistency level is specified then the
> {{AbstractWriteResponesHandler}} will contain a delegate WriteResponseHandler
> that tracks whether the ideal consistency level is met before a write times
> out. It also tracks the latency for achieving the ideal CL of successful
> writes.
> These two metrics would be reported on a per keyspace basis.
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