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From "Jason Brown (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13632) Digest mismatch if row is empty
Date Tue, 12 Sep 2017 21:05:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13632?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16163650#comment-16163650
] 

Jason Brown commented on CASSANDRA-13632:
-----------------------------------------

[~whangsf] Can you provide steps to reproduce? Also, what kind of improvement did you see
when you applied your patch? Specific numbers would be great! 

wrt to thrift, are you using CQL over thrift, or old-school thrift a la astyanx/hector/pycassa?
I tried to dig up a thrift client but it was pretty painful and I stopped.



> Digest mismatch if row is empty
> -------------------------------
>
>                 Key: CASSANDRA-13632
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13632
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Local Write-Read Paths
>            Reporter: Andrew Whang
>            Assignee: Andrew Whang
>             Fix For: 3.0.x
>
>
> This issue is similar to CASSANDRA-12090. Quorum read queries that include a column selector
(non-wildcard) result in digest mismatch when the row is empty (key does not exist). It seems
the data serialization path checks if rowIterator.isEmpty() and if so ignores column names
(by setting IS_EMPTY flag). However, the digest serialization path does not perform this check
and includes column names. The digest comparison results in a mismatch. The mismatch does
not end up issuing a read repair mutation since the underlying data is the same.
> The mismatch on the read path ends up doubling our p99 read latency. We discovered this
issue while testing a 2.2.5 to 3.0.13 upgrade.
> One thing to note is that we're using thrift, which ends up handling the ColumnFilter
differently than the CQL path. 
> As with CASSANDRA-12090, fixing the digest seems sensible.



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