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https://issues.apache.org/jira/browse/CASSANDRA-1123?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13184347#comment-13184347
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Jonathan Ellis commented on CASSANDRA-1123:
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Definitely.
I think we can do two things with this:
# Answer "what is taking so long with query X"
# Automatically enable tracing for say 1% of all queries and look for patterns
(2) is important because often (1) is not repeatable, if the slowness comes
from hitting disk for instance it will usually be cached the next time.
I think we're 90% of the way there with this, but log files aren't very
programatically accessible, i.e., it's difficult to implement scenario (2).
I'd like to
- make enable_logging method return the query context id
- store trace results in a columnfamily keyed by the id so they can be
retrieved and displayed (e.g. by adding EXPLAIN command to cqlsh, which would
be a separate ticket)
What do you think?
> 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: Aaron Morton
> Fix For: 1.2
>
> Attachments: 1123-3.patch.gz
>
>
> 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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