[
https://issues.apache.org/jira/browse/CASSANDRA-4316?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13549228#comment-13549228
]
Jonathan Ellis commented on CASSANDRA-4316:
-------------------------------------------
Looks like mayThrottle (both implementations) is missing conversion from bytes
-> MB. (Actually looking at the RateLimiter creation, it looks like the name
{{dataSizeInMB}} is misleading since it is actually still bytes.)
Does StandaloneScrubber ratelimit? It probably shouldn't.
Scanner in cleanup compaction needs a withRateLimit.
Is looping over scanner.getCurrentPosition for each row compacted going to eat
CPU? Maybe every N rows would be better, with N = 1MB / average row size.
Quite possibly it's not actually a problem and I'm prematurely complexifying.
Nits:
- "// throttle if needed" comment is redundant
- "maybeThrottle" is a better method name than "mayThrottle"
- May be able to simplify getCompactionRateLimiter by creating a default
limiter even if we are unthrottled (since if we are unthrottled we ignore it
anyway), so you don't need to worry about == null checks
Rest LGTM. Should we open a new ticket to move FST to RateLimiter and get rid
of Throttle entirely?
> Compaction Throttle too bursty with large rows
> ----------------------------------------------
>
> Key: CASSANDRA-4316
> URL: https://issues.apache.org/jira/browse/CASSANDRA-4316
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Affects Versions: 0.8.0
> Reporter: Wayne Lewis
> Assignee: Yuki Morishita
> Fix For: 1.2.1
>
> Attachments: 4316-1.2.txt
>
>
> In org.apache.cassandra.db.compaction.CompactionIterable the check for
> compaction throttling occurs once every 1000 rows. In our workload this is
> much too large as we have many large rows (16 - 100 MB).
> With a 100 MB row, about 100 GB is read (and possibly written) before the
> compaction throttle sleeps. This causes bursts of essentially unthrottled
> compaction IO followed by a long sleep which yields inconsistence performance
> and high error rates during the bursts.
> We applied a workaround to check throttle every row which solved our
> performance and error issues:
> line 116 in org.apache.cassandra.db.compaction.CompactionIterable:
> if ((row++ % 1000) == 0)
> replaced with
> if ((row++ % 1) == 0)
> I think the better solution is to calculate how often throttle should be
> checked based on the throttle rate to apply sleeps more consistently. E.g. if
> 16MB/sec is the limit then check for sleep after every 16MB is read so sleeps
> are spaced out about every second.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira
