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https://issues.apache.org/jira/browse/CASSANDRA-2401?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13029366#comment-13029366
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Sylvain Lebresne commented on CASSANDRA-2401:
---------------------------------------------

Comments on the patch:
  * ignoreObsoleteMutation() now forgot to actually remove the obsolete 
mutation from cf.
  * not sure why mutatedIndexColumns need to be concurrent. There is no 
concurrency in ignoreObsoleteMutation, is there ?
  * really minor: change to debug log "Scanning index row %s ..." seems 
misleading since the first argument is not a row name.

Other than that, I do agree with you that there is quite probably a race 
between reads and concurrent writes. But also agree that it doesn't seem to be 
the problem here

> getColumnFamily() return null, which is not checked in ColumnFamilyStore.java 
> scan() method, causing Timeout Exception in query
> -------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-2401
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2401
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: 0.7.0
>         Environment: Hector 0.7.0-28, Cassandra 0.7.4, Windows 7, Eclipse
>            Reporter: Tey Kar Shiang
>            Assignee: Jonathan Ellis
>             Fix For: 0.7.6
>
>         Attachments: 2401.txt
>
>
> ColumnFamilyStore.java, line near 1680, "ColumnFamily data = 
> getColumnFamily(new QueryFilter(dk, path, firstFilter))", the data is 
> returned null, causing NULL exception in "satisfies(data, clause, primary)" 
> which is not captured. The callback got timeout and return a Timeout 
> exception to Hector.
> The data is empty, as I traced, I have the the columns Count as 0 in 
> removeDeletedCF(), which return the null there. (I am new and trying to 
> understand the logics around still). Instead of crash to NULL, could we 
> bypass the data?
> About my test:
> A stress-test program to add, modify and delete data to keyspace. I have 30 
> threads simulate concurrent users to perform the actions above, and do a 
> query to all rows periodically. I have Column Family with rows (as File) and 
> columns as index (e.g. userID, fileType).
> No issue on the first day of test, and stopped for 3 days. I restart the test 
> on 4th day, 1 of the users failed to query the files (timeout exception 
> received). Most of the users are still okay with the query.

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