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https://issues.apache.org/jira/browse/CASSANDRA-4734?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13475633#comment-13475633
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Sylvain Lebresne commented on CASSANDRA-4734:
---------------------------------------------
Basically the motivations of #4448 were that:
# it seems that in most case the best granularity where to define a default
consistency is the CF level. I.e. I think we want users to be able to define a
per-CF default CL.
# It seems sane to me to keep the property that client library shouldn't have
to parse queries. That were I first though this ticket changed something, but
it doesn't. Because if a client library want to offer ways to define a per-CF
CL, it would have to parse each queries to know to which CF the query applies
to to know which CL to use.
# If we agree that 1. is desirable and even ignoring 2., it's simpler for users
to set the per-CF default CL once in the schema than in which client library
you use.
> Move CQL3 consistency to protocol
> ---------------------------------
>
> Key: CASSANDRA-4734
> URL: https://issues.apache.org/jira/browse/CASSANDRA-4734
> Project: Cassandra
> Issue Type: Task
> Components: API
> Reporter: Jonathan Ellis
> Assignee: Sylvain Lebresne
> Fix For: 1.2.0 beta 2
>
> Attachments: 0001-Move-consistency-level-to-the-protocol-level-2.txt,
> 0001-Move-consistency-level-to-the-protocol-level.txt,
> 0002-Remove-remains-of-4448.txt, 0002-Thrift-generated-file-diffs-2.txt,
> 0003-Thrift-generated-file-diffs.txt
>
>
> Currently, in CQL3, you set the consistency level of an operation in
> the language, eg 'SELECT * FROM foo USING CONSISTENCY QUORUM'. It now
> looks like this was a mistake, and that consistency should be set at
> the protocol level, i.e. as a separate parameter along with the query.
> The reasoning is that the CL applies to the guarantee provided by the
> operation being successful, not to the query itself. Specifically,
> having the CL being part of the language means that CL is opaque to
> low level client libraries without themselves parsing the CQL, which
> we want to avoid. Thus,
> - Those libraries can't implement automatic retries policy, where a query
> would be retried with a smaller CL. (I'm aware that this is often a Bad
> Idea, but it does have legitimate uses and not having that available is seen
> as a regression from the Thrift api.)
> - We had to introduce CASSANDRA-4448 to allow the client to configure some
> form of default CL since the library can't handle that anymore, which is
> hackish.
> - Executing prepared statements with different CL requires preparing multiple
> statements.
> - CL only makes sense for BATCH operations as a whole, not the sub-statements
> within the batch. Currently CQL3 "fixes" that by validating the given CLs
> match, but it would be much more clear if the CL was on the protocol side.
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