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https://issues.apache.org/jira/browse/CASSANDRA-193?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12780912#action_12780912
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Stu Hood edited comment on CASSANDRA-193 at 11/22/09 3:07 AM:
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EDIT: After a little more consideration, the caching bug had nothing to do with
our hash function. It was a disconnect between the binary tree, and the b-tree
we are using to store it. To be honest, I don't want to merge something so
complex that even the person who created it still has trouble reasoning about
it.
I'm going to refactor the b-tree into a binary tree tomorrow.
was (Author: stuhood):
The comment explains it better, but you need something like XOR, which is
associative: (1 ^ 2) ^ 3 == 1 ^ (2 ^ 3) in order to cache partially computed
values. MD5 needs to be computed sequentially over all of the inputs, so it can
be used for leaves, but not inner nodes.
> 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,
> 193-1-tree-preparation.diff, 193-2-tree.diff, 193-2-tree.diff,
> 193-3-aes-preparation.diff, 193-3-aes-preparation.diff, 193-4-aes.diff,
> 193-4-aes.diff, 193-5-manual-repair.diff, 193-6-inverted-filter.diff,
> 193-6-inverted-filter.diff, 193-7-disable-caching-and-fix-minimum-token.diff,
> 193-breakdown.txt, 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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