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From "Jay Zhuang (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-8119) More Expressive Consistency Levels
Date Fri, 02 Jun 2017 00:32:04 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8119?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16033967#comment-16033967
] 

Jay Zhuang edited comment on CASSANDRA-8119 at 6/2/17 12:31 AM:
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I'd like to propose another DC wise consistency level, like {{$dc-wise-cl}}-{{$local-dc-cl}}.
Similar to {{each_quorum}}, for example {{quorum_quorum}} means quorum number of DC meets
quorum, so the {{quorum_quorum}} read/write could tolerate one dc down. And {{quorum_one}}
means quorum number of DC meets CL one.
I think this is going to be useful for the clusters with 3 DCs or more. Right now, we have
to use global quorum for that. [~thobbs] [~iamaleksey] what do you think? Seems this cannot
be covered by this the "CL map" or "CL UDF", I can create another ticket if it makes sense.


was (Author: jay.zhuang):
I'd like to propose another DC wise consistency level, like {{$dc-wise-cl}}-{{$local-dc-cl}}.
Similar to {{each_quorum}}, {{quorum_quorum}} means quorum number of DC meets quorum, so the
{{quorum_quorum}} read/write could tolerate one dc down. And {{quorum_one}} means quorum number
of DC meets CL one.
I think this is going to be useful for the clusters with 3 DCs or more. Right now, we have
to use global quorum for that. [~thobbs] [~iamaleksey] what do you think? Seems this cannot
be covered by this the "CL map" or "CL UDF", I can create another ticket if it makes sense.

> 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: 4.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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