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From "Sylvain Lebresne (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-4734) Move CQL3 consistency to protocol
Date Fri, 12 Oct 2012 18:03:04 GMT


Sylvain Lebresne updated CASSANDRA-4734:

    Attachment:     (was: 0001-Move-consistency-level-to-the-protocol-level-2.txt)
> Move CQL3 consistency to protocol
> ---------------------------------
>                 Key: CASSANDRA-4734
>                 URL:
>             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,
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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