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From "Pavel Yaskevich (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-2749) fine-grained control over data directories
Date Tue, 16 Aug 2011 16:29:35 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-2749?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13085812#comment-13085812
] 

Pavel Yaskevich commented on CASSANDRA-2749:
--------------------------------------------

After crushing my head again this for a few days I can say that this is more complicated that
it sounds for a few reasons:

 - We will need to support both old/new directory structures which requires major changes
in the way how Descriptor class works and how CFS and SSTable classes do file lookup and path
generation.
 - Adds additional complexity to the way how we do backups, snapshots and recover which could
potentially lead to some nasty bugs.
 - As Peter already mentioned "Cassandra won't be able to distinguish between an actual empty
CF and a directory that wasn't mounted (or a symlink pointing to a non-mounted directory)".

There are more but those mentioned are major ones. Let's skip this for now.

> fine-grained control over data directories
> ------------------------------------------
>
>                 Key: CASSANDRA-2749
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2749
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Pavel Yaskevich
>            Priority: Minor
>
> Currently Cassandra supports multiple data directories but no way to control what sstables
are placed where. Particularly for systems with mixed SSDs and rotational disks, it would
be nice to pin frequently accessed columnfamilies to the SSDs.
> Postgresql does this with tablespaces (http://www.postgresql.org/docs/9.0/static/manage-ag-tablespaces.html)
but we should probably avoid using that name because of confusing similarity to "keyspaces."

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