[jira] [Commented] (CASSANDRA-14554) LifecycleTransaction encounters ConcurrentModificationException when used in multi-threaded context

["Benedict (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-14554?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16710665#comment-16710665 ] 

Benedict commented on CASSANDRA-14554:
--------------------------------------

[~krummas]: Could you take a look at [this line|https://github.com/apache/cassandra/compare/cassandra-3.11...stef1927:db-2633-3.11#diff-5d2d6808d387dcbd1937ee23496ac10aR95]?  It looks like it was introduced in CASSANDRA-6696, but I'm not sure why?

I'll be posting a 3.0, 3.11 and trunk patch tomorrow.

Stefania, are you comfortable with calling the new interface {{LifecycleNewTracker}}?  Or do you have another proposal?  I'd simply prefer a term that doesn't clash so strongly with {{Tracker}} which is a much more general concept.

> LifecycleTransaction encounters ConcurrentModificationException when used in multi-threaded context
> ---------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-14554
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-14554
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Streaming and Messaging
>            Reporter: Dinesh Joshi
>            Assignee: Dinesh Joshi
>            Priority: Major
>             Fix For: 4.0, 3.0.x, 3.11.x
>
>
> When LifecycleTransaction is used in a multi-threaded context, we encounter this exception -
> {quote}java.util.ConcurrentModificationException: null
>  at java.util.LinkedHashMap$LinkedHashIterator.nextNode(LinkedHashMap.java:719)
>  at java.util.LinkedHashMap$LinkedKeyIterator.next(LinkedHashMap.java:742)
>  at java.lang.Iterable.forEach(Iterable.java:74)
>  at org.apache.cassandra.db.lifecycle.LogReplicaSet.maybeCreateReplica(LogReplicaSet.java:78)
>  at org.apache.cassandra.db.lifecycle.LogFile.makeRecord(LogFile.java:320)
>  at org.apache.cassandra.db.lifecycle.LogFile.add(LogFile.java:285)
>  at org.apache.cassandra.db.lifecycle.LogTransaction.trackNew(LogTransaction.java:136)
>  at org.apache.cassandra.db.lifecycle.LifecycleTransaction.trackNew(LifecycleTransaction.java:529)
> {quote}
> During streaming we create a reference to a {{LifeCycleTransaction}} and share it between threads -
> [https://github.com/apache/cassandra/blob/5cc68a87359dd02412bdb70a52dfcd718d44a5ba/src/java/org/apache/cassandra/db/streaming/CassandraStreamReader.java#L156]
> This is used in a multi-threaded context inside {{CassandraIncomingFile}} which is an {{IncomingStreamMessage}}. This is being deserialized in parallel.
> {{LifecycleTransaction}} is not meant to be used in a multi-threaded context and this leads to streaming failures due to object sharing. On trunk, this object is shared across all threads that transfer sstables in parallel for the given {{TableId}} in a {{StreamSession}}. There are two options to solve this - make {{LifecycleTransaction}} and the associated objects thread safe, scope the transaction to a single {{CassandraIncomingFile}}. The consequences of the latter option is that if we experience streaming failure we may have redundant SSTables on disk. This is ok as compaction should clean this up. A third option is we synchronize access in the streaming infrastructure.



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