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https://issues.apache.org/jira/browse/CASSANDRA-11226?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sylvain Lebresne updated CASSANDRA-11226:
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Status: Patch Available (was: Open)
Patch is [here|https://github.com/pcmanus/cassandra/commits/11226]. I went with
option 2: we don't really support humongous amounts of tables in the first
place and as you said, it's not a performance sensible tool in the first place.
Plus, while this might maybe be improvement, the current implementation
iterates over all tables of all keyspaces no matter what ends up being
displayed, so it's not like this patch will have any performance impact on the
status quo.
I took the liberty to do a few cleanups while at it btw. And the patch is
against trunk: not convinced it's worth backporting given that it's been the
way it is forever and that in theory changing the numbers in a minor/bug fix
release feels not nice.
> nodetool tablestats' keyspace-level metrics are wrong/misleading
> ----------------------------------------------------------------
>
> Key: CASSANDRA-11226
> URL: https://issues.apache.org/jira/browse/CASSANDRA-11226
> Project: Cassandra
> Issue Type: Bug
> Components: Tools
> Reporter: Tyler Hobbs
> Assignee: Sylvain Lebresne
> Priority: Minor
> Labels: lhf
> Fix For: 2.2.x, 3.0.x, 3.x
>
>
> In the nodetool tablestats output (formerly cfstats), we display "keyspace"
> level metrics before the table-level metrics:
> {noformat}
> Keyspace: testks
> Read Count: 14772528
> Read Latency: 0.14456651623879135 ms.
> Write Count: 4761283
> Write Latency: 0.062120404521218336 ms.
> Pending Flushes: 0
> Table: processes
> SSTable count: 7
> Space used (live): 496.76 MB
> Space used (total): 496.76 MB
> Space used by snapshots (total): 0 bytes
> Off heap memory used (total): 285.76 KB
> SSTable Compression Ratio: 0.2318241570710227
> Number of keys (estimate): 3027
> Memtable cell count: 2140
> Memtable data size: 1.66 MB
> Memtable off heap memory used: 0 bytes
> Memtable switch count: 967
> Local read count: 14772528
> Local read latency: 0.159 ms
> Local write count: 4761283
> Local write latency: 0.068 ms
> {noformat}
> However, the keyspace-level metrics are misleading, at best. They are
> aggregate metrics for every table in the keyspace _that is included in the
> command line filters_. So, if you run {{tablestats}} for a single table, the
> keyspace-level stats will only reflect that table's stats.
> I see two possible fixes:
> # If the command line options don't include the entire keyspace, skip the
> keyspace-level stats
> # Ignore the command line options, and always make the keyspace-level stats
> an aggregate of all tables in the keyspace
> My only concern with option 2 is that performance may suffer a bit on
> keyspaces with many tables. However, this is a command line tool, so as long
> as the response time is reasonable, I don't think it's a big deal.
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