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From "John Chakerian (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-3750) Migrations and Schema CFs use disk space proportional to the square of the number of CFs
Date Wed, 18 Jan 2012 05:10:40 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-3750?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

John Chakerian updated CASSANDRA-3750:
--------------------------------------

    Attachment: fit.png
    
> 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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