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From "Avi Kivity (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-13550) Partition-level isolation of batch writes almost impossible to use
Date Wed, 24 May 2017 08:30:04 GMT
Avi Kivity created CASSANDRA-13550:
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             Summary: Partition-level isolation of batch writes almost impossible to use
                 Key: CASSANDRA-13550
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13550
             Project: Cassandra
          Issue Type: Bug
          Components: Documentation and Website
            Reporter: Avi Kivity


The documentation for the {{BATCH}} statement states:

bq. All updates in a @BATCH@ belonging to a given partition key are performed in isolation.

However, it is almost impossible to make use of this guarantee while reading:
 - if paging is enabled, then the server may insert a page boundary at any point; and there
is no isolation among different pages of a single query
 - repairs can cause individual rows within a partition to be repaired, even if they belonged
to a larger isolated update
 - in Cassandra 3 and above, reconciliation is incremental, again breaking isolation
 - if rows are overwritten, then even row-level isolation is not guaranteed (the old timestamp
collision problem)

While it's possible to write an application that makes use of the existing isolation guarantees,
it is very hard, and will likely impose constraints on the application (paging must be disabled
and overwrites and row-level deletes never used).

The rules should be clarified here and relaxed; relaxation could allow a more efficient implementation
(in Scylla we went full MVCC) and prevent users from relying on a guarantee that is not in
fact provided.



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