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From Tom van den Berge <tom.vandenbe...@gmail.com>
Subject Re: How to prevent queries being routed to new DC?
Date Tue, 08 Sep 2015 07:35:37 GMT
Hi Anuj,

That could indeed explain reads on my new DC. However, what I'm seeing in
my client application is that every now and then, a read query does not
produce any result, while I'm sure that it should. If I understand the read
repair process correctly, it will never cause a read query fail to find a
replica, right?



On Tue, Sep 8, 2015 at 4:40 AM, Anuj Wadehra <anujw_2003@yahoo.co.in> wrote:

> Hi Tom,
>
> While reading data ( even at CL LOCAL_QUORUM), if data in different nodes
> required to meet CL in your local cluster doesnt match, data will be read
> from remote dc for read repair if read_repair_chance is not 0.
>
> Imp points:
> 1.If you are reading and writing at local_quorum you can set
> read_repair_chance to 0 to prevent cross dc read repair.
> 2. For enabling dc local read repairs you can use
> dclocal_read_repair_chance and set read_repair_chance to 0.
> 3. If you are experiencing frequent requests being routed due to digest
> mismatch you may need to investigate mutation drops in your cluster using
> tpstats.
>
> Refer to similar issue raised by us :
> https://issues.apache.org/jira/browse/CASSANDRA-8479
>
> Thanks
> Anuj
>
> Sent from Yahoo Mail on Android
> <https://overview.mail.yahoo.com/mobile/?.src=Android>
> ------------------------------
> *From*:"Tom van den Berge" <tom@drillster.com>
> *Date*:Tue, 8 Sep, 2015 at 1:31 am
> *Subject*:Re: How to prevent queries being routed to new DC?
>
> NetworkTopologyStrategy
>
> On Mon, Sep 7, 2015 at 4:39 PM, Ryan Svihla <rs@foundev.pro> wrote:
>
>> What's your keyspace replication strategy?
>>
>> On Thu, Sep 3, 2015 at 3:16 PM Tom van den Berge <
>> tom.vandenberge@gmail.com> wrote:
>>
>>> Thanks for your help so far!
>>>
>>> I have some problems trying to understand the jira mentioned by Rob :(
>>>
>>> I'm currently trying to set up the first node in the new DC with
>>> auto_bootstrap = true. The node then becomes visible with status "joining",
>>> which (hopefully) prevents other DCs from sending queries to it.
>>>
>>> Do you think this will work?
>>>
>>>
>>>
>>> On Thu, Sep 3, 2015 at 9:46 PM, Robert Coli <rcoli@eventbrite.com>
>>> wrote:
>>>
>>>> On Thu, Sep 3, 2015 at 12:25 PM, Bryan Cheng <bryan@blockcypher.com>
>>>> wrote:
>>>>
>>>>> I'd recommend you enable tracing and do a few queries in a controlled
>>>>> environment to verify that queries are being routed to your new nodes.
>>>>> Provided you have followed the procedure outlined above (specifically,
have
>>>>> set auto_bootstrap to false in your new cluster), rebuild has not been
run,
>>>>> the application is not connecting to the new cluster, and all your queries
>>>>> are run at LOCAL_* quorum levels, I do not believe those queries should
be
>>>>> routed to the new dc.
>>>>>
>>>>
>>>> Other than CASSANDRA-9753, this is true.
>>>>
>>>> https://issues.apache.org/jira/browse/CASSANDRA-9753 (Unresolved; ):
>>>> "LOCAL_QUORUM reads can block cross-DC if there is a digest mismatch"
>>>>
>>>> =Rob
>>>>
>>>>
>>> --
>> Regards,
>>
>> Ryan Svihla
>
>
>
>
> --
> Tom van den Berge
> Lead Software Engineer
>  [image: Drillster] Middenburcht 136
> 3452 MT Vleuten
> Netherlands+31 30 755 53 30
> www.drillster.com [image: Follow us on Facebook] Follow us on Facebook
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