support incremental repair controlled by external agent
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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
Attachments: CASSANDRA-3912-trunk-v1.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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