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From "Stu Hood (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-193) Proactive repair
Date Tue, 17 Nov 2009 07:29:39 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-193?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12778749#action_12778749
] 

Stu Hood commented on CASSANDRA-193:
------------------------------------

> 1. To get us started, can we trigger a Merkle tree repair manually from nodeprobe.
I got most of this working tonight: the code needed some serious cleanup in order to not duplicate
effort or send trees back and forth in an infinite loop.

> 4. The code needs to be better documented.
Next patch should be improved in this area.

> 5. You need to name variables and methods better. For example...
These were particularly bad... you're right. I've changed them.

> 6. In MerkleTree.difference(), shouldn't you add a case that returns an empty diff when
the trees are consistent?
Good catch.

I'll wrap up a new version of this patch on Tuesday before COB, I promise.

> Proactive repair
> ----------------
>
>                 Key: CASSANDRA-193
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-193
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Stu Hood
>             Fix For: 0.5
>
>         Attachments: 193-1-tree-preparation.diff, 193-2-tree.diff, 193-3-aes-preparation.diff,
193-4-aes.diff, mktree-and-binary-tree.png
>
>
> Currently cassandra supports "read repair," i.e., lazy repair when a read is done.  This
is better than nothing but is not sufficient for some cases (e.g. catastrophic node failure
where you need to rebuild all of a node's data on a new machine).
> Dynamo uses merkle trees here.  This is harder for Cassandra given the CF data model
but I suppose we could just hash the serialized CF value.

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