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From "Michael Greene (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-279) finish snapshot support
Date Fri, 17 Jul 2009 04:17:14 GMT


Michael Greene commented on CASSANDRA-279:

I'm definitely going to need this to play nicely with Windows (if not support, then at least
fail gracefully) and can test (or write before committed) the functionality if Sammy can't.

What's the intended use of these snapshots?  Restoration at a later date?  Is that scoped
to Cassandra or nodeprobe, or would that be a manual process?

> finish snapshot support
> -----------------------
>                 Key: CASSANDRA-279
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Sammy Yu
>         Attachments: 0001-Work-for-CASSANDRA-279.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:
>  * add something to list the snapshots available via JMX
>  * optionally make this all per-Table instead of per-database

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