For what its worth, the problem isn't the snitch it's the replication strategy - he's using the right snitch but SimpleStrategy ignores it
That's the same reason that adding a new DC doesn't work - the relocation strategy is dc agnostic and changing it safely IS the problem -- Jeff Jirsa > On Sep 18, 2017, at 11:46 AM, Jon Haddad <jonathan.had...@gmail.com> wrote: > > 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 > > 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> 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>: >>> >>> 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> 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.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>: >>> >>> 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> 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>: >>>> >>>> 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> 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 >>>>> >>>>> 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 >>>>> >>>>> 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 >
