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From "Sylvain Lebresne (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-3912) support incremental repair controlled by external agent
Date Mon, 16 Apr 2012 14:44:17 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-3912?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13254729#comment-13254729
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Sylvain Lebresne commented on CASSANDRA-3912:
---------------------------------------------

bq.  the solution is for the user to look at the cluster layout, and use exact tokens, right?

Well, kinda. The user should look at the layout, grab one of the range of the node, and then
submit repair on a subset of that range. I fully agree this is not for the faint of heart
(which is why I prefer not exposing it to nodetool just yet), but as it stand I'll admit I'm
not sure how to improve that error message much.

bq. it should be possible to repair a range that falls on the boundary of two getLocalRanges,
assuming it can be fully contained in their aggregate

Actually no. Or more precisely, in general it still have the problem mentioned above. Given
2 local ranges, there will be some neighbors that share one but not both of those ranges (so
with these nodes the repair would be imprecise). In other words, to repair a range on the
boundary of two local ranges, you'd really want to do 2 repairs on each subrange, because
each time the set of neighbors will be different (we could do that splitting at the StorageService
level but we should probably keep it simple for now. I see this ticket as just exposing existing
code to advanced user, not reinventing repair).

bq. For JMX's sake.

Fixed :) (I've rebased the patch)

bq. Would including the 'future.session.getName' in this log message be useful

That's logged before the session is created.
                
> support incremental repair controlled by external agent
> -------------------------------------------------------
>
>                 Key: CASSANDRA-3912
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3912
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Peter Schuller
>            Assignee: Peter Schuller
>             Fix For: 1.2
>
>         Attachments: 3912_v2.txt, CASSANDRA-3912-trunk-v1.txt, CASSANDRA-3912-v2-001-add-nodetool-commands.txt,
CASSANDRA-3912-v2-002-fix-antientropyservice.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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