For those of you who like trivia, simpleSnitch is hard coded to report every node in DC in “datacenter1” and in rack “rack1”, there’s no way around it. https://github.com/apache/cassandra/blob/8b3a60b9a7dbefeecc06bace617279612ec7092d/src/java/org/apache/cassandra/locator/SimpleSnitch.java#L28 <https://github.com/apache/cassandra/blob/8b3a60b9a7dbefeecc06bace617279612ec7092d/src/java/org/apache/cassandra/locator/SimpleSnitch.java#L28>
I would do this by setting up a new DC, trying to do it with the existing one is going to leave you in a state where most queries will return incorrect results (2/3 of queries at ONE and 1/2 of queries at QUORUM) until you finish repair. > On Sep 18, 2017, at 11:41 AM, Jeff Jirsa <jji...@gmail.com> wrote: > > The hard part here is nobody's going to be able to tell you exactly what's > involved in fixing this because nobody sees your ring > > And since you're using vnodes and have a nontrivial number of instances, > sharing that ring (and doing anything actionable with it) is nontrivial. > > If you weren't using vnodes, you could just fix the distribution and decom > extra nodes afterward. > > I thought - but don't have time or energy to check - that the ec2snitch would > be rack aware even when using simple strategy - if that's not the case (as > you seem to indicate), then you're in a weird spot - you can't go to NTS > trivially because doing so will reassign your replicas to be rack/as aware, > certainly violating your consistency guarantees. > > If you can change your app to temporarily write with ALL and read with ALL, > and then run repair, then immediately ALTER the keyspace, then run repair > again, then drop back to whatever consistency you're using, you can probably > get through it. The challenge is that ALL gets painful if you lose any > instance. > > But please test in a lab, and note that this is inherently dangerous, I'm not > advising you to do it, though I do believe it can be made to work. > > > > > > -- > Jeff Jirsa > > > On Sep 18, 2017, at 11:18 AM, Dominik Petrovic > <dominik.petro...@mail.ru.INVALID <mailto:dominik.petro...@mail.ru.INVALID>> > wrote: > >> @jeff what do you think is the best approach here to fix this problem? >> Thank you all for helping me. >> >> >> Thursday, September 14, 2017 3:28 PM -07:00 from kurt greaves >> <k...@instaclustr.com <mailto:k...@instaclustr.com>>: >> >> Sorry that only applies our you're using NTS. You're right that simple >> strategy won't work very well in this case. To migrate you'll likely need to >> do a DC migration to ensuite no downtime, as replica placement will change >> even if RF stays the same. >> >> On 15 Sep. 2017 08:26, "kurt greaves" <k...@instaclustr.com >> <mailto:k...@instaclustr.com>> wrote: >> If you have racks configured and lose nodes you should replace the node with >> one from the same rack. You then need to repair, and definitely don't >> decommission until you do. >> >> Also 40 nodes with 256 vnodes is not a fun time for repair. >> >> On 15 Sep. 2017 03:36, "Dominik Petrovic" <dominik.petro...@mail.ru >> <mailto:dominik.petro...@mail.ru>.invalid> wrote: >> @jeff, >> I'm using 3 availability zones, during the life of the cluster we lost >> nodes, retired others and we end up having some of the data >> written/replicated on a single availability zone. We saw it with nodetool >> getendpoints. >> Regards >> >> >> Thursday, September 14, 2017 9:23 AM -07:00 from Jeff Jirsa >> <jji...@gmail.com <mailto:jji...@gmail.com>>: >> >> With one datacenter/region, what did you discover in an outage you think >> you'll solve with network topology strategy? It should be equivalent for a >> single D.C. >> >> -- >> Jeff Jirsa >> >> >> On Sep 14, 2017, at 8:47 AM, Dominik Petrovic >> <dominik.petro...@mail.ru.INVALID <mailto:dominik.petro...@mail.ru.INVALID>> >> wrote: >> >>> Thank you for the replies! >>> >>> @jeff my current cluster details are: >>> 1 datacenter >>> 40 nodes, with vnodes=256 >>> RF=3 >>> What is your advice? is it a production cluster, so I need to be very >>> careful about it. >>> Regards >>> >>> >>> Thu, 14 Sep 2017 -2:47:52 -0700 from Jeff Jirsa <jji...@gmail.com >>> <mailto:jji...@gmail.com>>: >>> >>> The token distribution isn't going to change - the way Cassandra maps >>> replicas will change. >>> >>> How many data centers/regions will you have when you're done? What's your >>> RF now? You definitely need to run repair before you ALTER, but you've got >>> a bit of a race here between the repairs and the ALTER, which you MAY be >>> able to work around if we know more about your cluster. >>> >>> How many nodes >>> How many regions >>> How many replicas per region when you're done? >>> >>> >>> >>> >>> -- >>> Jeff Jirsa >>> >>> >>> On Sep 13, 2017, at 2:04 PM, Dominik Petrovic >>> <dominik.petro...@mail.ru.INVALID >>> <mailto:dominik.petro...@mail.ru.INVALID>> wrote: >>> >>>> Dear community, >>>> I'd like to receive additional info on how to modify a keyspace >>>> replication strategy. >>>> >>>> My Cassandra cluster is on AWS, Cassandra 2.1.15 using vnodes, the >>>> cluster's snitch is configured to Ec2Snitch, but the keyspace the >>>> developers created has replication class SimpleStrategy = 3. >>>> >>>> During an outage last week we realized the discrepancy between the >>>> configuration and we would now fix the issue using >>>> NetworkTopologyStrategy. >>>> >>>> What are the suggested steps to perform? >>>> For Cassandra 2.1 I found only this doc: >>>> http://docs.datastax.com/en/cassandra/2.1/cassandra/operations/opsChangeKSStrategy.html >>>> >>>> <http://docs.datastax.com/en/cassandra/2.1/cassandra/operations/opsChangeKSStrategy.html> >>>> >>>> that does not mention anything about repairing the cluster >>>> >>>> For Cassandra 3 I found this other doc: >>>> https://docs.datastax.com/en/cassandra/3.0/cassandra/operations/opsChangeKSStrategy.html >>>> >>>> <https://docs.datastax.com/en/cassandra/3.0/cassandra/operations/opsChangeKSStrategy.html> >>>> >>>> That involves also the cluster repair operation. >>>> >>>> On a test cluster I tried the steps for Cassandra 2.1 but the token >>>> distribution in the ring didn't change so I'm assuming that wasn't the >>>> right think to do. >>>> I also perform a nodetool repair -pr but nothing changed as well. >>>> Some advice? >>>> >>>> -- >>>> Dominik Petrovic >>> >>> >>> -- >>> Dominik Petrovic >> >> >> -- >> Dominik Petrovic >> >> >> -- >> Dominik Petrovic
