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From Paulo Motta <>
Subject Re: best way to measure repair times?
Date Thu, 19 Mar 2015 19:53:08 GMT
Repair and the fine print

At first glance, it may appear that Hinted Handoff lets you safely get away
without needing repair. This is only true if you never have hardware
failure. Hardware failure means that

   1. We lose “historical” data for which the write has already finished,
   so there is nothing to tell the rest of the cluster exactly what data has
   gone missing
   2. We can also lose hints-not-yet-replayed from requests the failed node

With sufficient dedication, you can get by with “only run repair after
hardware failure and rely on hinted handoff the rest of the time,” but as
your clusters grow (and hardware failure becomes more common) performing
repair as a one-off special case will become increasingly difficult to do
perfectly. Thus, we continue to recommend running a full repair weekly.

2015-03-19 16:42 GMT-03:00 Robert Coli <>:

> On Thu, Mar 19, 2015 at 12:13 PM, Ali Akhtar <> wrote:
>> Cassandra doesn't guarantee eventual consistency?
> If you run regularly scheduled repair, it does. If you do not run repair,
> it does not.
> Hinted handoff, for example, is considered an optimization for repair, and
> does not assert that it provides a consistency guarantee.
> =Rob

Paulo Ricardo

European Master in Distributed Computing

*Royal Institute of Technology - KTH*
*Instituto Superior Técnico - IST*
* <>*

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