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From "Aleksey Yeschenko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13595) Implement short read protection on partition boundaries
Date Fri, 29 Sep 2017 17:38:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13595?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16186125#comment-16186125
] 

Aleksey Yeschenko commented on CASSANDRA-13595:
-----------------------------------------------

[~beobal] Sorry, it was indeed a little unclear. {{forShortReadRetry()}} was modified to retain
the per partition limit, so asking for more rows then the limit no longer worked, and made
the code a bit confusing.

It also just happens that that arbitrary minimum was bothering me anyway. We should probably
not go beyond the limit set by the user - unless we know for sure that it is safe. But until
we are smarter about this, and start taking row sizes into account, I feel uneasy about enforcing
arbitrary minimums.

Pushed another commit on top that addresses two issues:
1. An NPE when trying to perform SRP on an empty iterator ({{lastPartitionKey}} would be null)
2. Lack of a reliable stop condition causing looping

With the change all relevant dtests are passing locally.

> Implement short read protection on partition boundaries
> -------------------------------------------------------
>
>                 Key: CASSANDRA-13595
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13595
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Coordination
>            Reporter: Andrés de la Peña
>            Assignee: Aleksey Yeschenko
>              Labels: Correctness
>             Fix For: 3.0.15, 3.11.1
>
>
> It seems that short read protection doesn't work when the short read is done at the end
of a partition in a range query. The final assertion of this dtest fails:
> {code}
> def short_read_partitions_delete_test(self):
>         cluster = self.cluster
>         cluster.set_configuration_options(values={'hinted_handoff_enabled': False})
>         cluster.set_batch_commitlog(enabled=True)
>         cluster.populate(2).start(wait_other_notice=True)
>         node1, node2 = self.cluster.nodelist()
>         session = self.patient_cql_connection(node1)
>         create_ks(session, 'ks', 2)
>         session.execute("CREATE TABLE t (k int, c int, PRIMARY KEY(k, c)) WITH read_repair_chance
= 0.0")
>         # we write 1 and 2 in a partition: all nodes get it.
>         session.execute(SimpleStatement("INSERT INTO t (k, c) VALUES (1, 1)", consistency_level=ConsistencyLevel.ALL))
>         session.execute(SimpleStatement("INSERT INTO t (k, c) VALUES (2, 1)", consistency_level=ConsistencyLevel.ALL))
>         # we delete partition 1: only node 1 gets it.
>         node2.flush()
>         node2.stop(wait_other_notice=True)
>         session = self.patient_cql_connection(node1, 'ks', consistency_level=ConsistencyLevel.ONE)
>         session.execute(SimpleStatement("DELETE FROM t WHERE k = 1"))
>         node2.start(wait_other_notice=True)
>         # we delete partition 2: only node 2 gets it.
>         node1.flush()
>         node1.stop(wait_other_notice=True)
>         session = self.patient_cql_connection(node2, 'ks', consistency_level=ConsistencyLevel.ONE)
>         session.execute(SimpleStatement("DELETE FROM t WHERE k = 2"))
>         node1.start(wait_other_notice=True)
>         # read from both nodes
>         session = self.patient_cql_connection(node1, 'ks', consistency_level=ConsistencyLevel.ALL)
>         assert_none(session, "SELECT * FROM t LIMIT 1")
> {code}
> However, the dtest passes if we remove the {{LIMIT 1}}.
> Short read protection [uses a {{SinglePartitionReadCommand}}|https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/service/DataResolver.java#L484],
maybe it should use a {{PartitionRangeReadCommand}} instead?



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