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https://issues.apache.org/jira/browse/CASSANDRA-1123?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13443184#comment-13443184
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Jonathan Ellis commented on CASSANDRA-1123:
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bq. after I had done this I realized that there was no point

the point was that an exception from a FutureTask will not be seen unless get() 
is called, or we do some extra gymnastics a la DTPE.  So what we want the 
tracing executor to do is to logExceptionsAfterExecute like DTPE, but we only 
want that to be logged to a file, we don't want to try to insert it as a 
tracing event.
                
> Allow tracing query details
> ---------------------------
>
>                 Key: CASSANDRA-1123
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1123
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: David Alves
>             Fix For: 1.2.0 beta 1
>
>         Attachments: 1123-3.patch.gz, 1123.patch, 1123.patch, 1123.patch, 
> 1123.patch, 1123-v6.txt, 1123-v7.patch
>
>
> In the spirit of CASSANDRA-511, it would be useful to tracing on queries to 
> see where latency is coming from: how long did row cache lookup take?  key 
> search in the index?  merging the data from the sstables?  etc.
> The main difference vs setting debug logging is that debug logging is too big 
> of a hammer; by turning on the flood of logging for everyone, you actually 
> distort the information you're looking for.  This would be something you 
> could set per-query (or more likely per connection).
> We don't need to be as sophisticated as the techniques discussed in the 
> following papers but they are interesting reading:
> http://research.google.com/pubs/pub36356.html
> http://www.usenix.org/events/osdi04/tech/full_papers/barham/barham_html/
> http://www.usenix.org/event/nsdi07/tech/fonseca.html

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