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Date: Wed, 3 Oct 2012 02:55:07 +1100 (NCT)
From: "Jonathan Ellis (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
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Subject: [jira] [Commented] (CASSANDRA-4734) Move CQL3 consistency to
 protocol
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    [ https://issues.apache.org/jira/browse/CASSANDRA-4734?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13467811#comment-13467811 ] 

Jonathan Ellis commented on CASSANDRA-4734:
-------------------------------------------

bq. it's probably worth duplicating that one too and removing set_cql_version

+1

bq. I'm not sure how to properly support both the new and old methods

Ugh.

Guess we can take a YAGNI approach -- we've been pretty clear that cql3 might change from 1.1 to 1.2, but we can always backport to 1.1.x later if someone needs it badly enough.
                
> 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.txt, 0002-Remove-remains-of-4448.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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