[
https://issues.apache.org/jira/browse/CASSANDRA-1391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13149904#comment-13149904
]
Jonathan Ellis commented on CASSANDRA-1391:
-------------------------------------------
For example, suppose we have two clients C1 and C2, and two nodes A and B.
They have a columnfamily that includes the following options:
{noformat}
ColumnFamily1: {
'default_validation_class': 'bytes',
'comment': 'an example',
'row_cache_size': 0
}
{noformat}
Next, C1 and C2 update ColumnFamily1 with M1 and M2 as follows:
{noformat}
M1 = ColumnFamily1: {'d_v_c': 'ascii', 'comment': 'foo'} @ T1}}
M2 = ColumnFamily1: {'d_v_c': 'utf8', 'row_cache_size': 1000000} @ T0 < T1
{noformat}
(Note that we have a conflict on default_validation_class.)
Node A receives M1 first, while node B receives M2 first.
*Node A:*
{noformat}
(applies M1)
ColumnFamily1: {
'default_validation_class': 'ascii',
'comment': 'foo',
'row_cache_size': 0
}
(applies M2)
ColumnFamily1: {
'default_validation_class': 'ascii', // M2.dvc has no effect since T0 < T1
'comment': 'foo',
'row_cache_size': 1000000
}
{noformat}
*Node B:*
{noformat}
ColumnFamily1: {
'default_validation_class': 'utf8',
'comment': 'an example',
'row_cache_size': 1000000
}
(applies M1)
ColumnFamily1: {
'default_validation_class': 'ascii',
'comment': 'foo',
'row_cache_size': 1000000
}
{noformat}
Because timestamp-based conflict resolution is commutative, all nodes end with
the same schema no matter what order they get the updates in.
> Allow Concurrent Schema Migrations
> ----------------------------------
>
> Key: CASSANDRA-1391
> URL: https://issues.apache.org/jira/browse/CASSANDRA-1391
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Affects Versions: 0.7.0
> Reporter: Stu Hood
> Assignee: Pavel Yaskevich
> Fix For: 1.1
>
> Attachments: CASSANDRA-1391.patch
>
>
> CASSANDRA-1292 fixed multiple migrations started from the same node to
> properly queue themselves, but it is still possible for migrations initiated
> on different nodes to conflict and leave the cluster in a bad state. Since
> the system_add/drop/rename methods are accessible directly from the client
> API, they should be completely safe for concurrent use.
> It should be possible to allow for most types of concurrent migrations by
> converting the UUID schema ID into a VersionVectorClock (as provided by
> CASSANDRA-580).
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators:
https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira
