J.B. Langston created CASSANDRA-5087:
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Summary: 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: 1.2.0 rc1, 1.1.8, 1.0.10
Reporter: J.B. Langston
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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