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From "Tyler Hobbs (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-11226) nodetool tablestats' keyspace-level metrics are wrong/misleading
Date Wed, 24 Feb 2016 22:00:19 GMT
Tyler Hobbs created CASSANDRA-11226:
---------------------------------------

             Summary: 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
            Priority: Minor
             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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