[
https://issues.apache.org/jira/browse/CASSANDRA-4734?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13475286#comment-13475286
]
Jonathan Ellis commented on CASSANDRA-4734:
-------------------------------------------
To elaborate: ConsistencyLevel is part of application logic, not data model.
So it really belongs in the protocol and client layer, which is where this
ticket pushes it.
Pushing it into CFMetadata in 4448 was consistent with "it's part of the data
model / query language" approach we used to take, but now that we're fixing
that it no longer makes sense to enshrine it server-side.
> 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.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira
