@Rob: Thanks about the feedback.

Yet I have a weird behavior still unexplained about repairing. Are counters supposed to be "repaired" too ? I mean, while reading at CL.ONE I can have different values depending on what node is answering. Even after a read repair or a full repair. Shouldn't a repair fix these discrepancies ?

The only way I found to get always the same count is to read data at CL.QUORUM, but this is a workaround since the data itself remains wrong on some nodes. 

Any clue on it ?


2013/5/15 Edward Capriolo <edlinuxguru@gmail.com>

Introduced Active Anti-Entropy. Riak now has active anti-entropy. In distributed systems, inconsistencies can arise between replicas due to failure modes, concurrent updates, and physical data loss or corruption. Pre-1.3 Riak already had several features for repairing this “entropy”, but they all required some form of user intervention. Riak 1.3 introduces automatic, self-healing properties that repair entropy on an ongoing basis.

On Wed, May 15, 2013 at 5:32 PM, Robert Coli <rcoli@eventbrite.com> wrote:
On Wed, May 15, 2013 at 1:27 AM, Alain RODRIGUEZ <arodrime@gmail.com> wrote:
> Rob, I was wondering something. Are you a commiter working on improving the
> repair or something similar ?

I am not a committer [1], but I have an active interest in potential
improvements to the best practices for repair. The specific change
that I am considering is a modification to the default
gc_grace_seconds value, which seems picked out of a hat at 10 days. My
view is that the current implementation of repair has such negative
performance consequences that I do not believe that holding onto
tombstones for longer than 10 days could possibly be as bad as the
fixed cost of running repair once every 10 days. I believe that this
value is too low for a default (it also does not map cleanly to the
work week!) and likely should be increased to 14, 21 or 28 days.

> Anyway, if a commiter (or any other expert) could give us some feedback on
> our comments (Are we doing well or not, whether things we observe are normal
> or unexplained, what is going to be improved in the future about repair...)

1) you are doing things according to best practice
2) unfortunately your experience with significantly degraded
performance, including a blocked go-live due to repair bloat is pretty
3) the things you are experiencing are part of the current
implementation of repair and are also typical, however I do not
believe they are fully "explained" [2]
4) as has been mentioned further down thread, there are discussions
regarding (and some already committed) improvements to both the
current repair paradigm and an evolution to a new paradigm

Thanks to all for the responses so far, please keep them coming! :D

[1] hence the (unofficial) tag for this thread. I do have minor
patches accepted to the codebase, but always merged by an actual
committer. :)
[2] driftx@#cassandra feels that these things are explained/understood
by core team, and points to
https://issues.apache.org/jira/browse/CASSANDRA-5280 as a useful
approach to minimize same.