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From Ben Slater <ben.sla...@instaclustr.com>
Subject Re: read repair with consistency one
Date Sat, 21 Apr 2018 23:45:22 GMT
I haven't checked the code to make sure this is still the case but last
time I checked:
- For any read, if an inconsistency between replicas is detected then this
inconsistency will be repaired. This obviously wouldn’t apply with CL=ONE
because you’re not reading multiple replicas to find inconsistencies.
- If read_repair_chance or dc_local_read_repair_chance are >0 then extra
replicas are checked as part of the query for the % of queries specified by
the chance setting. Again, if inconsistencies are found, they are repaired.
I expect this mechanism would still apply for CL=ONE.


Cheers
Ben

On Sat, 21 Apr 2018 at 22:20 Grzegorz Pietrusza <gpietrusza@gmail.com>
wrote:

> I haven't asked about "regular" repairs. I just wanted to know how read
> repair behaves in my configuration (or is it doing anything at all).
>
> 2018-04-21 14:04 GMT+02:00 Rahul Singh <rahul.xavier.singh@gmail.com>:
>
>> Read repairs are one anti-entropy measure. Continuous repairs is another.
>> If you do repairs via Reaper or your own method it will resolve your
>> discrepencies.
>>
>> On Apr 21, 2018, 3:16 AM -0400, Grzegorz Pietrusza <gpietrusza@gmail.com>,
>> wrote:
>>
>> Hi all
>>
>> I'm a bit confused with how read repair works in my case, which is:
>> - multiple DCs with RF 1 (NetworkTopologyStrategy)
>> - reads with consistency ONE
>>
>>
>> The article #1 says that read repair in fact runs RF reads for some
>> percent of the requests. Let's say I have read_repair_chance = 0.1. Does
>> it mean that 10% of requests will be read in all DCs (digest) and processed
>> in a background?
>>
>> On the other hand article #2 says that for consistency ONE read repair is
>> not performed. Does it mean that in my case read repair does not work at
>> all? Is there any way to enable read repair across DCs and stay will
>> consistency ONE for reads?
>>
>>
>> #1 https://www.datastax.com/dev/blog/common-mistakes-and-misconceptions
>> #2
>> https://docs.datastax.com/en/cassandra/3.0/cassandra/operations/opsRepairNodesReadRepair.html
>>
>> Regards
>> Grzegorz
>>
>>
> --


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