[jira] [Commented] (CASSANDRA-13289) Make it possible to monitor an ideal consistency level separate from actual consistency level

["Romain Hardouin (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-13289?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15894255#comment-15894255 ] 

Romain Hardouin commented on CASSANDRA-13289:
---------------------------------------------

Very interesting! 
Do you have an idea of the overhead that this monitoring layer would add? If this adds too much overhead we should be able to enable/disable it at runtime via nodetool.

> 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: Bug
>          Components: Core
>            Reporter: Ariel Weisberg
>            Assignee: Ariel Weisberg
>
> 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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