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https://issues.apache.org/jira/browse/CASSANDRA-14647?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16596400#comment-16596400
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Marcus Eriksson commented on CASSANDRA-14647:
---------------------------------------------
Looks like this can happen when the table metric `EstimatedPartitionCount` is
[queried
|https://github.com/apache/cassandra/blob/d049c6b9b4af4f663aac2bf90d860c3b0c20684a/src/java/org/apache/cassandra/metrics/TableMetrics.java#L307]
- it grabs the CANONICAL sstables without referencing them, so if there are
very many sstables some might get compacted away while calculating the
partition count and we get this warning
If this is the case it is not really a problem (other than the annoying warn
message in the log files)
[~rha] could you verify that you are querying this metric?
[~rha] / [~nezdali] could you pause querying this metric and check if the error
stops appearing?
Thanks for providing the logs over email btw [~nezdali]
> Reading cardinality from Statistics.db failed
> ---------------------------------------------
>
> Key: CASSANDRA-14647
> URL: https://issues.apache.org/jira/browse/CASSANDRA-14647
> Project: Cassandra
> Issue Type: Bug
> Components: Compaction
> Environment: Clients are doing only writes with Local One, cluster
> consist of 3 regions with RF3.
> Storage is configured wth jbod/XFS on 10 x 1Tb disks
> IOPS limit for each disk 500 (total 5000 iops)
> Bandwith for each disk 60mb/s (600 total)
> OS is Debian linux.
> Reporter: Vitali Djatsuk
> Priority: Major
> Fix For: 3.0.x
>
> Attachments: cassandra_compaction_pending_tasks_7days.png
>
>
> There is some issue with sstable metadata which is visible in system.log, the
> messages says:
> {noformat}
> WARN [Thread-6] 2018-07-25 07:12:47,928 SSTableReader.java:249 - Reading
> cardinality from Statistics.db failed for
> /opt/data/disk5/data/keyspace/table/mc-big-Data.db.{noformat}
> Although there is no such file.
> The message has appeared after i've changed the compaction strategy from
> SizeTiered to Leveled. Compaction strategy has been changed region by region
> (total 3 regions) and it has coincided with the double client write traffic
> increase.
> I have tried to run nodetool scrub to rebuilt the sstable, but that does not
> fix the issue.
> So very hard to define the steps to reproduce, probably it will be:
> # run stress tool with write traffic
> # under load change compaction strategy from SireTiered to Leveled for the
> bunch of hosts
> # add more write traffic
> Reading the code it is said that if this metadata is broken, then "estimating
> the keys will be done using index summary".
>
> [https://github.com/apache/cassandra/blob/cassandra-3.0.17/src/java/org/apache/cassandra/io/sstable/format/SSTableReader.java#L247]
>
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