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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-279) finish snapshot support
Date Tue, 21 Jul 2009 21:11:14 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12733826#action_12733826
] 

Jonathan Ellis commented on CASSANDRA-279:
------------------------------------------

we already have 

<data dir>/<table>

heirarchy for the normal table data, let's put snapshots under that instead of having a separate
tree with its own per-table area

<data dir>/<table>/<snapshots>/<snapshot tag>/<sstable files>

> finish snapshot support
> -----------------------
>
>                 Key: CASSANDRA-279
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-279
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Sammy Yu
>         Attachments: 0001-Work-for-CASSANDRA-279.patch, 0001-Work-for-CASSANDRA-279.patch,
0002-Work-for-CASSANDRA-279.patch, 0003-Patch-for-Cassandra-279-3rd.patch, 279-3.patch
>
>
> searching for "snapshot" in *.java shows a bunch of code for supporting snapshots via
hard links.
> (this works b/c SSTables are immutable, once created.)
> this used to be more complete but when we dropped the JDK7 requirement we just removed
the code that we couldn't do in JDK6 and hard link support was one of those.
> So what you would need to do here is:
>  * create a hard link method (using Runtime.exec("ln") on linux / os x I imagine)
>  * add a JMX hook to invoke this on the data files (this is where looking at the old
codebase might help); ColumnFamilyStoreMBean.forceFlush is an example of an "Action" jmx interface.
using jconsole to interact with JMX stuff is explained here: http://wiki.apache.org/cassandra/MemtableThresholds
>  * add something to list the snapshots available via JMX
>  * optionally make this all per-Table instead of per-database

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