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https://issues.apache.org/jira/browse/CASSANDRA-13632?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16166318#comment-16166318
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Jason Brown edited comment on CASSANDRA-13632 at 9/14/17 1:39 PM:
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bq. 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.
This is correct.
bq. The digest comparison results in a mismatch.
This is not correct. In
[{{DigestResolver}}|https://github.com/apache/cassandra/blob/cassandra-3.0/src/java/org/apache/cassandra/service/DigestResolver.java#L87],
the coordinator gets the digest from each response, even for the data that
sent back the full {{DataResponse}}. So, while there is the difference in what
the data nodes send back to the coordindator, it resolves to the same digest
value.
[~whangsf] what indications do you have that a DigestMismatch is happening?
was (Author: jasobrown):
bq. 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.
This is correct.
bq. The digest comparison results in a mismatch.
This is not correct. In
[{{DigestResolver}}|https://github.com/apache/cassandra/blob/cassandra-3.0/src/java/org/apache/cassandra/service/DigestResolver.java#L87],
the coordinator gets the digest from each response, even for the data that
sent back the full {{DataResponse}}. So, while there is the difference in what
the data nodes send back to the coordindator, is resolves to the same digest
value.
[~whangsf] what indications do you have that a DigestMismatch is happening?
> 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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