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From "David Alves (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-1123) Allow tracing query details
Date Tue, 28 Aug 2012 06:21:09 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1123?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13442983#comment-13442983
] 

David Alves commented on CASSANDRA-1123:
----------------------------------------

ran some smoke tests (locally): 0.1% tracing probability under full load causes ~5.5% slowdown
(in writes), without any tracing event being discarded.


                
> 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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