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https://issues.apache.org/jira/browse/CASSANDRA-8119?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15331969#comment-15331969
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Tyler Hobbs commented on CASSANDRA-8119:
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bq. this is a niche requirement
I disagree. Good multi-datacenter support is one of Cassandra's most popular
features. Having the ability to control consistency levels per-DC can be very
useful.
bq. Additionally, you can't really encapsulate it in a UDF, as there are more
factors that are CL-dependent. The behaviour of read repair, and speculative
retry, can/should wary a lot depending on a CL
I don't think the CL should be _only_ a UDF. Other options could be specified
through {{WITH}} clauses. For example, something like {{WITH READ REPAIR =
'dclocal'}}. I'm just making that up, but we do have a lot of flexibility here.
bq. Also, while you could stick it to schema, I don't see how it's a fit,
conceptually, and not a (conceptually) dirty hack.
I'm not sure what you mean. Care to elaborate?
> More Expressive Consistency Levels
> ----------------------------------
>
> Key: CASSANDRA-8119
> URL: https://issues.apache.org/jira/browse/CASSANDRA-8119
> Project: Cassandra
> Issue Type: New Feature
> Components: CQL
> Reporter: Tyler Hobbs
> Fix For: 3.x
>
>
> For some multi-datacenter environments, the current set of consistency levels
> are too restrictive. For example, the following consistency requirements
> cannot be expressed:
> * LOCAL_QUORUM in two specific DCs
> * LOCAL_QUORUM in the local DC plus LOCAL_QUORUM in at least one other DC
> * LOCAL_QUORUM in the local DC plus N remote replicas in any DC
> I propose that we add a new consistency level: CUSTOM. In the v4 (or v5)
> protocol, this would be accompanied by an additional map argument. A map of
> {DC: CL} or a map of {DC: int} is sufficient to cover the first example. If
> we accept a special keys to represent "any datacenter", the second case can
> be handled. A similar technique could be used for "any other nodes".
> I'm not in love with the special keys, so if anybody has ideas for something
> more elegant, feel free to propose them. The main idea is that we want to be
> flexible enough to cover any reasonable consistency or durability
> requirements.
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