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From Anuj Wadehra <anujw_2...@yahoo.co.in>
Subject Re: How to prevent queries being routed to new DC?
Date Tue, 08 Sep 2015 02:40:47 GMT
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

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 
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