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From Grzegorz Pietrusza <gpietru...@gmail.com>
Subject Re: read repair with consistency one
Date Wed, 25 Apr 2018 18:23:40 GMT
Hi Ben

Thanks a lot. From my analysis of the code it looks like you are right.
When global read repair kicks in all live endpoints are queried for data,
regardless of consistency level.  Only EACH_QUORUM is treated differently.

Cheers
Grzegorz

2018-04-22 1:45 GMT+02:00 Ben Slater <ben.slater@instaclustr.com>:

> 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
>>>
>>>
>> --
>
>
> *Ben Slater*
>
> *Chief Product Officer <https://www.instaclustr.com/>*
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