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Posted to commits@cassandra.apache.org by "Jonathan Ellis (JIRA)" <ji...@apache.org> on 2012/08/02 16:35:03 UTC
[jira] [Comment Edited] (CASSANDRA-4482) In-memory merkle trees for
repair
[ https://issues.apache.org/jira/browse/CASSANDRA-4482?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13427347#comment-13427347 ]
Jonathan Ellis edited comment on CASSANDRA-4482 at 8/2/12 2:34 PM:
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This is how the original Dynamo paper describes maintaining merkle trees. The problem that Acunu doesn't mention is that this forces you to do read and rehash all the rows sharing the tree leaf with row X, whenever any row X is updated. So you are trading sequential i/o for random i/o... not a good move, unless you assume SSD or a small dataset (and even then, you're rehashing many rows on each update, not just one, so it's far from clear that this is a good trade).
I'm a bigger fan of the continuous repair approach enabled by CASSANDRA-3912, and discussed in CASSANDRA-2699 (although i think 2699 overcomplicates things).
was (Author: jbellis):
This is how the original Dynamo paper describes maintaining merkle trees. The problem that Acunu doesn't mention is that this forces you to do read and rehash all the rows sharing the tree leaf with row X, whenever any row X is updated. So you are trading sequential i/o for random i/o... not a good move, unless you assume SSD or a small dataset (and even then, you're rehashing many rows on each update, not just one).
I'm a bigger fan of the continuous repair approach enabled by CASSANDRA-3912, and discussed in CASSANDRA-2699 (although i think 2699 overcomplicates things).
> In-memory merkle trees for repair
> ---------------------------------
>
> Key: CASSANDRA-4482
> URL: https://issues.apache.org/jira/browse/CASSANDRA-4482
> Project: Cassandra
> Issue Type: New Feature
> Reporter: Marcus Eriksson
>
> this sounds cool, we should reimplement it in the open source cassandra;
> http://www.acunu.com/2/post/2012/07/incremental-repair.html
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