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From "Jonathan Ellis (Commented) (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-3912) support incremental repair controlled by external agent
Date Tue, 27 Mar 2012 13:34:28 GMT


Jonathan Ellis commented on CASSANDRA-3912:

True, but if we're doing smaller chunks of data we may be able to tolerate some imprecision.
 We already have a little, since it's quite unlikely that snapshots of actively-updated CFs
across multiple replicas contain *exactly* the same updates.
> support incremental repair controlled by external agent
> -------------------------------------------------------
>                 Key: CASSANDRA-3912
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Peter Schuller
>            Assignee: Peter Schuller
>             Fix For: 1.2
>         Attachments: CASSANDRA-3912-trunk-v1.txt, CASSANDRA-3912-v2-001-add-nodetool-commands.txt,
> As a poor man's pre-cursor to CASSANDRA-2699, exposing the ability to repair small parts
of a range is extremely useful because it allows (with external scripting logic) to slowly
repair a node's content over time. Other than avoiding the bulkyness of complete repairs,
it means that you can safely do repairs even if you absolutely cannot afford e.g. disk spaces
spikes (see CASSANDRA-2699 for what the issues are).
> Attaching a patch that exposes a "repairincremental" command to nodetool, where you specify
a step and the number of total steps. Incrementally performing a repair in 100 steps, for
example, would be done by:
> {code}
> nodetool repairincremental 0 100
> nodetool repairincremental 1 100
> ...
> nodetool repairincremental 99 100
> {code}
> An external script can be used to keep track of what has been repaired and when. This
should allow (1) allow incremental repair to happen now/soon, and (2) allow experimentation
and evaluation for an implementation of CASSANDRA-2699 which I still think is a good idea.
This patch does nothing to help the average deployment, but at least makes incremental repair
possible given sufficient effort spent on external scripting.
> The big "no-no" about the patch is that it is entirely specific to RandomPartitioner
and BigIntegerToken. If someone can suggest a way to implement this command generically using
the Range/Token abstractions, I'd be happy to hear suggestions.
> An alternative would be to provide a nodetool command that allows you to simply specify
the specific token ranges on the command line. It makes using it a bit more difficult, but
would mean that it works for any partitioner and token type.
> Unless someone can suggest a better way to do this, I think I'll provide a patch that
does this. I'm still leaning towards supporting the simple "step N out of M" form though.

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