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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