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" <t...@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 <r...@foundev.pro> wrote: What's your keyspace replication strategy? On Thu, Sep 3, 2015 at 3:16 PM Tom van den Berge <tom.vandenbe...@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 <rc...@eventbrite.com> wrote: On Thu, Sep 3, 2015 at 12:25 PM, Bryan Cheng <br...@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  Middenburcht 136 3452 MT Vleuten Netherlands+31 30 755 53 30 www.drillster.com  Follow us on Facebook
