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From "John Chakerian (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-3750) Migrations and Schema CFs use disk space proportional to the square of the number of CFs
Date Wed, 18 Jan 2012 05:10:39 GMT
Migrations and Schema CFs use disk space proportional to the square of the number of CFs
----------------------------------------------------------------------------------------

                 Key: CASSANDRA-3750
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3750
             Project: Cassandra
          Issue Type: Bug
          Components: Core
    Affects Versions: 1.0.1
         Environment: Linux (CentOS 5.7)
            Reporter: John Chakerian
         Attachments: fit.png

The system keyspace grows proportional to the square of the number of CFs (more likely, it
grows quadratically with # of schema changes in general). The major offenders in the keyspace
are the Migrations table & the Schema table. On clusters with very large #s of CFs (in
the low thousands), we think that these large system tables may be contributing to various
performance issues.

The approximate expression is: s = 0.0003253*n^2 + 2.58, where n is # of keyspaces + # of
schemas and s is the size of the system keyspace in megabytes. See attached plot of the regression
curve showing fit. 

Sampled data: 
{noformat}
NUM_CFS SYSTEM_SIZE_IN_MB
100 4.4
200 15
300 32
400 55
500 85
600 120
700 162
800 211
900 266
1000 327
{noformat}

This was hit in 1.0.1, but is almost certainly not version specific. 

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