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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Assigned] (CASSANDRA-11226) nodetool tablestats' keyspace-level metrics are wrong/misleading
Date Thu, 17 Mar 2016 09:49:33 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-11226?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Sylvain Lebresne reassigned CASSANDRA-11226:
--------------------------------------------

    Assignee: Sylvain Lebresne

> 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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