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From "Tyler Hobbs (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6483) Possible Collections.sort assertion failure in STCS.filterColdSSTables
Date Fri, 13 Dec 2013 21:38:07 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6483?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13847928#comment-13847928
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Tyler Hobbs commented on CASSANDRA-6483:
----------------------------------------

bq. Note that the CASSANDRA-6109 feature claims to be “off” by default, however it isn’t
immediately clear to me from that patch how “off” is implemented, and whether it is supposed
to go down that code path even when “off"

I answered this on the dev ML, but I'll repeat it here for others who are interested.  The
default max_cold_reads_ratio is 0.0, so {{filterColdSSTables()}} shouldn't filter any SSTables.
 When writing this patch, I realized that even with that set to 0.0, SSTables that have no
read activity at all would still be filtered out.  However, after this patch, that's no longer
true, and a setting of 0.0 will prevent any filtering at all.

bq. I’m guessing there is no actual downside (other than ERROR level messages in the logs
which cause alerts), since it just fails a subset of compactions?

That's correct, this shouldn't cause any other problems, only delay some compactions.

> Possible Collections.sort assertion failure in STCS.filterColdSSTables
> ----------------------------------------------------------------------
>
>                 Key: CASSANDRA-6483
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6483
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: graham sanderson
>            Assignee: Tyler Hobbs
>              Labels: compaction
>             Fix For: 2.0.4
>
>         Attachments: 6483-2.0-v1.patch
>
>
> We have observed the following stack trace periodically:
> {code}
> java.lang.IllegalArgumentException: Comparison method violates its general contract!
>         at java.util.TimSort.mergeLo(TimSort.java:747)
>         at java.util.TimSort.mergeAt(TimSort.java:483)
>         at java.util.TimSort.mergeCollapse(TimSort.java:410)
>         at java.util.TimSort.sort(TimSort.java:214)
>         at java.util.TimSort.sort(TimSort.java:173)
>         at java.util.Arrays.sort(Arrays.java:659)
>         at java.util.Collections.sort(Collections.java:217)
>         at org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy.filterColdSSTables(SizeTieredCompactionStrategy.java:94)
>         at org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy.getNextBackgroundSSTables(SizeTieredCompactionStrategy.java:59)
>         at org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy.getNextBackgroundTask(SizeTieredCompactionStrategy.java:229)
>         at org.apache.cassandra.db.compaction.CompactionManager$BackgroundCompactionTask.run(CompactionManager.java:191)
>         at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
>         at java.util.concurrent.FutureTask.run(FutureTask.java:262)
>         at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
>         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
>         at java.lang.Thread.run(Thread.java:744)
> {code}
> The comparator ant SizeTieredCompactionStrategy line 94 breaks the assertions in the
new JDK7 default sort algorithm, because (I think just) the hotness value (based on meter)
may be modified concurrently by another thread
> This bug appears to have been introduced in CASSANDRA-6109



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