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From "Peter Bailis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5455) Remove PBSPredictor
Date Sat, 25 May 2013 01:07:20 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5455?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13666888#comment-13666888
] 

Peter Bailis commented on CASSANDRA-5455:
-----------------------------------------

Okay. #1 will likely require more extensive code changes: basically, it'll require EstimatedHistograms
for each of the servers acting as replicas for a given ColumnFamily and will require EstimatedHistogram
tracing in the StorageProxy (to separate network-based latency from disk-based latency). Are
these changes feasible?

re: "a window of individual latency times," looking at the Metrics implementation of EstimatedHistogram,
EstimatedHistogram.values() should provide a reasonable enough sample (especially since, as
you mention, since it has other uses as well).

Perhaps the simplest strategy is to go with #3 for now but implement #1 in the future if there's
interest. #3 is easy; I've already written an example external module to do RTT/2 predictions:
https://github.com/pbailis/pbs-predictor/blob/9d31acd1667b08affa609278689b540d8e0380f5/pbspredictor/src/main/java/edu/berkeley/pbs/cassandra/CassandraLatencyTrace.java

                
> Remove PBSPredictor
> -------------------
>
>                 Key: CASSANDRA-5455
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5455
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Jonathan Ellis
>            Assignee: Jonathan Ellis
>             Fix For: 2.0
>
>         Attachments: 5455.txt
>
>
> It was a fun experiment, but it's unmaintained and the bar to understanding what is going
on is high.  Case in point: PBSTest has been failing intermittently for some time now, possibly
even since it was created.  Or possibly not and it was a regression from a refactoring we
did.  Who knows?

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