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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (CASSANDRA-5087) Changing from higher to lower compaction throughput causes long (multi hour) pause in large compactions
Date Thu, 27 Dec 2012 15:16:13 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-5087?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Jonathan Ellis resolved CASSANDRA-5087.
---------------------------------------

       Resolution: Fixed
    Fix Version/s: 1.2.1
                   1.1.9
         Reviewer: jbellis

Added comments and committed.  (Note: to 1.1.9 and 1.2.1, but not 1.2.0.)
                
> Changing from higher to lower compaction throughput causes long (multi hour) pause in
large compactions
> -------------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-5087
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5087
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: 0.8.0
>            Reporter: J.B. Langston
>            Assignee: J.B. Langston
>            Priority: Minor
>             Fix For: 1.1.9, 1.2.1
>
>
> We're running a major compaction against a column family that is 2.1TB (yes, I know it's
crazy huge, that's an entirely different discussion). During the evenings, we run a setcompactionthroughput
0 to unthrottle completely, and throttle again down to 20mb at the end of the maintenance
window. 
> Every morning we've come in to check progress, we find that the progress completely halts
as soon as the compaction throttling command is issued. Eventually, compaction continues.
I was looking at the throttling code, and I think I see the issue, but would like confirmation:
> throttleDelta (org.apache.cassandra.utils.Throttle.throttleDelta) sets a sleep time based
on the amount of data transferred since the last throttle time. Since we've gone from 20 MB
to wide open, and back to 20MB, the wait that is calculated is based on an attempt to average
the new throttling rate over the last 6.5 hours of running wide open.
> I think this could be fixed by adding a reset of bytesAtLastDelay and timeAtLastDelay
to the current values after the check at line 64:
> Current:
>         // if the target changed, log
>         if (newTargetBytesPerMS != targetBytesPerMS) 
>             logger.debug("{} target throughput now {} bytes/ms.", this, newTargetBytesPerMS);
>         targetBytesPerMS = newTargetBytesPerMS;
> New:
>  
>         // if the target changed, log
>         if (newTargetBytesPerMS != targetBytesPerMS) {
>             logger.debug("{} target throughput now {} bytes/ms.", this, newTargetBytesPerMS);
>             if(newTargetBytesPerMS < targetBytesPerMS || targetBytesPerMS < 1)
{
>             	bytesAtLastDelay += bytesDelta;
>             	timeAtLastDelay = System.currentTimeMillis();
>                 targetBytesPerMS = newTargetBytesPerMS;
>             	return;
>             }
>             targetBytesPerMS = newTargetBytesPerMS;
>         }
> Some redundancies that can be removed there, but I wanted to keep the approach local
to where I thought the problem was. 

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