Personally, I wouldn't ever do this. I recommend separate DCs if you want to keep workloads separate.
On Wed, Oct 23, 2019 at 4:06 PM Sergio <lapostadiser...@gmail.com> wrote: > I forgot to comment for > > OPTION C) > 1. Node DC RACK AZ 1 read ONE us-east-1a 2 read ONE us-east-1b > 2. 3 read ONE us-east-1c > 3. 4 write TWO us-east-1a 5 write TWO us-east-1b > 4. 6 write TWO us-east-1c I would expect that I need to decrease the > Consistency Level in the reads if one of the AZ goes down. Please consider > the below one as the real OPTION A. The previous one looks to be wrong > because the same rack is assigned to 2 different DC. > 5. OPTION A) > 6. Node DC RACK AZ 1 read ONE us-east-1a 2 read ONE us-east-1a > 7. 3 read ONE us-east-1a > 8. 4 write TWO us-east-1b 5 write TWO us-east-1b > 9. 6 write TWO us-east-1b > > > > Thanks, > > Sergio > > Il giorno mer 23 ott 2019 alle ore 12:33 Sergio <lapostadiser...@gmail.com> > ha scritto: > >> Hi Reid, >> >> Thank you very much for clearing these concepts for me. >> https://community.datastax.com/comments/1133/view.html I posted this >> question on the datastax forum regarding our cluster that it is unbalanced >> and the reply was related that the *number of racks should be a >> multiplier of the replication factor *in order to be balanced or 1. I >> thought then if I have 3 availability zones I should have 3 racks for each >> datacenter and not 2 (us-east-1b, us-east-1a) as I have right now or in the >> easiest way, I should have a rack for each datacenter. >> >> >> >> 1. Datacenter: live >> ================ >> Status=Up/Down >> |/ State=Normal/Leaving/Joining/Moving >> -- Address Load Tokens Owns Host ID >> Rack >> UN 10.1.20.49 289.75 GiB 256 ? >> be5a0193-56e7-4d42-8cc8-5d2141ab4872 us-east-1a >> UN 10.1.30.112 103.03 GiB 256 ? >> e5108a8e-cc2f-4914-a86e-fccf770e3f0f us-east-1b >> UN 10.1.19.163 129.61 GiB 256 ? >> 3c2efdda-8dd4-4f08-b991-9aff062a5388 us-east-1a >> UN 10.1.26.181 145.28 GiB 256 ? >> 0a8f07ba-a129-42b0-b73a-df649bd076ef us-east-1b >> UN 10.1.17.213 149.04 GiB 256 ? >> 71563e86-b2ae-4d2c-91c5-49aa08386f67 us-east-1a >> DN 10.1.19.198 52.41 GiB 256 ? >> 613b43c0-0688-4b86-994c-dc772b6fb8d2 us-east-1b >> UN 10.1.31.60 195.17 GiB 256 ? >> 3647fcca-688a-4851-ab15-df36819910f4 us-east-1b >> UN 10.1.25.206 100.67 GiB 256 ? >> f43532ad-7d2e-4480-a9ce-2529b47f823d us-east-1b >> So each rack label right now matches the availability zone and we >> have 3 Datacenters and 2 Availability Zone with 2 racks per DC but the >> above is clearly unbalanced >> If I have a keyspace with a replication factor = 3 and I want to >> minimize the number of nodes to scale up and down the cluster and keep it >> balanced should I consider an approach like OPTION A) >> 2. Node DC RACK AZ 1 read ONE us-east-1a 2 read ONE us-east-1a >> 3. 3 read ONE us-east-1a >> 4. 4 write ONE us-east-1b 5 write ONE us-east-1b >> 5. 6 write ONE us-east-1b >> 6. OPTION B) >> 7. Node DC RACK AZ 1 read ONE us-east-1a 2 read ONE us-east-1a >> 8. 3 read ONE us-east-1a >> 9. 4 write TWO us-east-1b 5 write TWO us-east-1b >> 10. 6 write TWO us-east-1b >> 11. *7 read ONE us-east-1c 8 write TWO us-east-1c* >> 12. *9 read ONE us-east-1c* Option B looks to be unbalanced and I >> would exclude it OPTION C) >> 13. Node DC RACK AZ 1 read ONE us-east-1a 2 read ONE us-east-1b >> 14. 3 read ONE us-east-1c >> 15. 4 write TWO us-east-1a 5 write TWO us-east-1b >> 16. 6 write TWO us-east-1c >> 17. >> >> >> so I am thinking of A if I have the restriction of 2 AZ but I guess >> that option C would be the best. If I have to add another DC for reads >> because we want to assign a new DC for each new microservice it would look >> like: >> OPTION EXTRA DC For Reads >> 1. Node DC RACK AZ 1 read ONE us-east-1a 2 read ONE us-east-1b >> 2. 3 read ONE us-east-1c >> 3. 4 write TWO us-east-1a 5 write TWO us-east-1b >> 4. 6 write TWO us-east-1c 7 extra-read THREE us-east-1a >> 5. 8 extra-read THREE us-east-1b >> 6. >> 7. >> >> >> 1. 9 extra-read THREE us-east-1c >> 2. >> The DC for *write* will replicate the data in the other datacenters. >> My scope is to keep the *read* machines dedicated to serve reads and >> *write* machines to serve writes. Cassandra will handle the >> replication for me. Is there any other option that is I missing or wrong >> assumption? I am thinking that I will write a blog post about all my >> learnings so far, thank you very much for the replies Best, Sergio >> >> >> Il giorno mer 23 ott 2019 alle ore 10:57 Reid Pinchback < >> rpinchb...@tripadvisor.com> ha scritto: >> >>> No, that’s not correct. The point of racks is to help you distribute >>> the replicas, not further-replicate the replicas. Data centers are what do >>> the latter. So for example, if you wanted to be able to ensure that you >>> always had quorum if an AZ went down, then you could have two DCs where one >>> was in each AZ, and use one rack in each DC. In your situation I think I’d >>> be more tempted to consider that. Then if an AZ went away, you could fail >>> over your traffic to the remaining DC and still be perfectly fine. >>> >>> >>> >>> For background on replicas vs racks, I believe the information you want >>> is under the heading ‘NetworkTopologyStrategy’ at: >>> >>> http://cassandra.apache.org/doc/latest/architecture/dynamo.html >>> >>> >>> >>> That should help you better understand how replicas distribute. >>> >>> >>> >>> As mentioned before, while you can choose to do the reads in one DC, >>> except for concerns about contention related to network traffic and >>> connection handling, you can’t isolate reads from writes. You can _ >>> *mostly*_ insulate the write DC from the activity within the read DC, >>> and even that isn’t an absolute because of repairs. However, your mileage >>> may vary, so do what makes sense for your usage pattern. >>> >>> >>> >>> R >>> >>> >>> >>> *From: *Sergio <lapostadiser...@gmail.com> >>> *Reply-To: *"user@cassandra.apache.org" <user@cassandra.apache.org> >>> *Date: *Wednesday, October 23, 2019 at 12:50 PM >>> *To: *"user@cassandra.apache.org" <user@cassandra.apache.org> >>> *Subject: *Re: Cassandra Rack - Datacenter Load Balancing relations >>> >>> >>> >>> *Message from External Sender* >>> >>> Hi Reid, >>> >>> Thanks for your reply. I really appreciate your explanation. >>> >>> We are in AWS and we are using right now 2 Availability Zone and not 3. >>> We found our cluster really unbalanced because the keyspace has a >>> replication factor = 3 and the number of racks is 2 with 2 datacenters. >>> We want the writes spread across all the nodes but we wanted the reads >>> isolated from the writes to keep the load on that node low and to be able >>> to identify problems in the consumers (reads) or producers (writes) >>> applications. >>> It looks like that each rack contains an entire copy of the data so this >>> would lead to replicate for each rack and then for each node the >>> information. If I am correct if we have a keyspace with 100GB and >>> Replication Factor = 3 and RACKS = 3 => 100 * 3 * 3 = 900GB >>> If I had only one rack across 2 or even 3 availability zone I would save >>> in space and I would have 300GB only. Please correct me if I am wrong. >>> >>> Best, >>> >>> Sergio >>> >>> >>> >>> Il giorno mer 23 ott 2019 alle ore 09:21 Reid Pinchback < >>> rpinchb...@tripadvisor.com> ha scritto: >>> >>> Datacenters and racks are different concepts. While they don't have to >>> be associated with their historical meanings, the historical meanings >>> probably provide a helpful model for understanding what you want from them. >>> >>> When companies own their own physical servers and have them housed >>> somewhere, the questions arise on where you want to locate any particular >>> server. It's a balancing act on things like network speed of related >>> servers being able to talk to each other, versus fault-tolerance of having >>> many servers not all exposed to the same risks. >>> >>> "Same rack" in that physical world tended to mean something like "all >>> behind the same network switch and all sharing the same power bus". The >>> morning after an electrical glitch fries a power bus and thus everything in >>> that rack, you realize you wished you didn't have so many of the same type >>> of server together. Well, they were servers. Now they are door stops. >>> Badness and sadness. >>> >>> That's kind of the mindset to have in mind with racks in Cassandra. >>> It's an artifact for you to separate servers into pools so that the >>> disparate pools have hopefully somewhat independent infrastructure risks. >>> However, all those servers are still doing the same kind of work, are the >>> same version, etc. >>> >>> Datacenters are amalgams of those racks, and how similar or different >>> they are from each other depends on what you want to do with them. What is >>> true is that if you have N datacenters, each one of them must have enough >>> disk storage to house all the data. The actual physical footprint of that >>> data in each DC depends on the replication factors in play. >>> >>> Note that you sorta can't have "one datacenter for writes" because the >>> writes will replicate across the data centers. You could definitely choose >>> to have only one that takes read queries, but best to think of writing as >>> being universal. One scenario you can have is where the DC not taking live >>> traffic read queries is the one you use for maintenance or performance >>> testing or version upgrades. >>> >>> One rack makes your life easier if you don't have a reason for multiple >>> racks. It depends on the environment you deploy into and your fault >>> tolerance goals. If you were in AWS and wanting to spread risk across >>> availability zones, then you would likely have as many racks as AZs you >>> choose to be in, because that's really the point of using multiple AZs. >>> >>> R >>> >>> >>> On 10/23/19, 4:06 AM, "Sergio Bilello" <lapostadiser...@gmail.com> >>> wrote: >>> >>> Message from External Sender >>> >>> Hello guys! >>> >>> I was reading about >>> https://urldefense.proofpoint.com/v2/url?u=https-3A__cassandra.apache.org_doc_latest_architecture_dynamo.html-23networktopologystrategy&d=DwIBaQ&c=9Hv6XPedRSA-5PSECC38X80c1h60_XWA4z1k_R1pROA&r=OIgB3poYhzp3_A7WgD7iBCnsJaYmspOa2okNpf6uqWc&m=xmgs1uQTlmvCtIoGJKHbByZZ6aDFzS5hDQzChDPCfFA&s=9ZDWAK6pstkCQfdbwLNsB-ZGsK64RwXSXfAkOWtmkq4&e= >>> >>> I would like to understand a concept related to the node load >>> balancing. >>> >>> I know that Jon recommends Vnodes = 4 but right now I found a >>> cluster with vnodes = 256 replication factor = 3 and 2 racks. This is >>> unbalanced because the racks are not a multiplier of the replication factor. >>> >>> However, my plan is to move all the nodes in a single rack to >>> eventually scale up and down the node in the cluster once at the time. >>> >>> If I had 3 racks and I would like to keep the things balanced I >>> should scale up 3 nodes at the time one for each rack. >>> >>> If I would have 3 racks, should I have also 3 different datacenters >>> so one datacenter for each rack? >>> >>> Can I have 2 datacenters and 3 racks? If this is possible one >>> datacenter would have more nodes than the others? Could it be a problem? >>> >>> I am thinking to split my cluster in one datacenter for reads and >>> one for writes and keep all the nodes in the same rack so I can scale up >>> once node at the time. >>> >>> >>> >>> Please correct me if I am wrong >>> >>> >>> >>> Thanks, >>> >>> >>> >>> Sergio >>> >>> >>> >>> --------------------------------------------------------------------- >>> >>> To unsubscribe, e-mail: user-unsubscr...@cassandra.apache.org >>> >>> For additional commands, e-mail: user-h...@cassandra.apache.org >>> >>> >>> >>> >>>
