Cost of availability is a fair question at some level of the discussion. In my experience, high availability is one of the top 2 or 3 reasons why Cassandra is chosen as the data solution. So, if I am given a Cassandra use case to build out, I would normally assume high availability is needed, even in a single data center scenario. Otherwise, there are other data options.
Sean R. Durity DB Solutions Staff Systems Engineer – Cassandra INTERNAL USE From: daemeon reiydelle <daeme...@gmail.com> Sent: Thursday, August 17, 2023 7:38 PM To: user@cassandra.apache.org Subject: [EXTERNAL] Re: Big Data Question I started to respond, then realized I and the other OP posters are not thinking the same: What is the business case for availability, data los/reload/recoverability? You all argue for higher availability and damn the cost. But noone asked "can I started to respond, then realized I and the other OP posters are not thinking the same: What is the business case for availability, data los/reload/recoverability? You all argue for higher availability and damn the cost. But noone asked "can you lose access, for 20 minutes, to a portion of the data, 10 times a year, on a 250 node cluster in AWS, if it is not lost"? Can you lose access 1-2 times a year for the cost of a 500 node cluster holding the same data? Then we can discuss 32/64g JVM and SSD's. . Arthur C. Clarke famously said that "technology sufficiently advanced is indistinguishable from magic." Magic is coming, and it's coming for all of us.... Daemeon Reiydelle email: daeme...@gmail.com<mailto:daeme...@gmail.com> LI: https://www.linkedin.com/in/daemeonreiydelle/ [linkedin.com]<https://urldefense.com/v3/__https:/www.linkedin.com/in/daemeonreiydelle/__;!!M-nmYVHPHQ!N1mRxPwl0tSfRLfEYnmvAswjcTP4hJoaD3cez01eFBEF_XdWXPbfExCyr_FrSTYe9KCKfOoNiLhaQPjzvUoMj-Q$> San Francisco 1.415.501.0198/Skype daemeon.c.m.reiydelle On Thu, Aug 17, 2023 at 1:53 PM Joe Obernberger <joseph.obernber...@gmail.com<mailto:joseph.obernber...@gmail.com>> wrote: Was assuming reaper did incremental? That was probably a bad assumption. nodetool repair -pr I know it well now! :) -Joe On 8/17/2023 4:47 PM, Bowen Song via user wrote: > I don't have experience with Cassandra on Kubernetes, so I can't > comment on that. > > For repairs, may I interest you with incremental repairs? It will make > repairs hell of a lot faster. Of course, occasional full repair is > still needed, but that's another story. > > > On 17/08/2023 21:36, Joe Obernberger wrote: >> Thank you. Enjoying this conversation. >> Agree on blade servers, where each blade has a small number of SSDs. >> Yeh/Nah to a kubernetes approach assuming fast persistent storage? I >> think that might be easier to manage. >> >> In my current benchmarks, the performance is excellent, but the >> repairs are painful. I come from the Hadoop world where it was all >> about large servers with lots of disk. >> Relatively small number of tables, but some have a high number of >> rows, 10bil + - we use spark to run across all the data. >> >> -Joe >> >> On 8/17/2023 12:13 PM, Bowen Song via user wrote: >>> The optimal node size largely depends on the table schema and >>> read/write pattern. In some cases 500 GB per node is too large, but >>> in some other cases 10TB per node works totally fine. It's hard to >>> estimate that without benchmarking. >>> >>> Again, just pointing out the obvious, you did not count the off-heap >>> memory and page cache. 1TB of RAM for 24GB heap * 40 instances is >>> definitely not enough. You'll most likely need between 1.5 and 2 TB >>> memory for 40x 24GB heap nodes. You may be better off with blade >>> servers than single server with gigantic memory and disk sizes. >>> >>> >>> On 17/08/2023 15:46, Joe Obernberger wrote: >>>> Thanks for this - yeah - duh - forgot about replication in my example! >>>> So - is 2TBytes per Cassandra instance advisable? Better to use >>>> more/less? Modern 2u servers can be had with 24 3.8TBtyte SSDs; so >>>> assume 80Tbytes per server, you could do: >>>> (1024*3)/80 = 39 servers, but you'd have to run 40 instances of >>>> Cassandra on each server; maybe 24G of heap per instance, so a >>>> server with 1TByte of RAM would work. >>>> Is this what folks would do? >>>> >>>> -Joe >>>> >>>> On 8/17/2023 9:13 AM, Bowen Song via user wrote: >>>>> Just pointing out the obvious, for 1PB of data on nodes with 2TB >>>>> disk each, you will need far more than 500 nodes. >>>>> >>>>> 1, it is unwise to run Cassandra with replication factor 1. It >>>>> usually makes sense to use RF=3, so 1PB data will cost 3PB of >>>>> storage space, minimal of 1500 such nodes. >>>>> >>>>> 2, depending on the compaction strategy you use and the write >>>>> access pattern, there's a disk space amplification to consider. >>>>> For example, with STCS, the disk usage can be many times of the >>>>> actual live data size. >>>>> >>>>> 3, you will need some extra free disk space as temporary space for >>>>> running compactions. >>>>> >>>>> 4, the data is rarely going to be perfectly evenly distributed >>>>> among all nodes, and you need to take that into consideration and >>>>> size the nodes based on the node with the most data. >>>>> >>>>> 5, enough of bad news, here's a good one. Compression will save >>>>> you (a lot) of disk space! >>>>> >>>>> With all the above considered, you probably will end up with a lot >>>>> more than the 500 nodes you initially thought. Your choice of >>>>> compaction strategy and compression ratio can dramatically affect >>>>> this calculation. >>>>> >>>>> >>>>> On 16/08/2023 16:33, Joe Obernberger wrote: >>>>>> General question on how to configure Cassandra. Say I have >>>>>> 1PByte of data to store. The general rule of thumb is that each >>>>>> node (or at least instance of Cassandra) shouldn't handle more >>>>>> than 2TBytes of disk. That means 500 instances of Cassandra. >>>>>> >>>>>> Assuming you have very fast persistent storage (such as a NetApp, >>>>>> PorterWorx etc.), would using Kubernetes or some orchestration >>>>>> layer to handle those nodes be a viable approach? Perhaps the >>>>>> worker nodes would have enough RAM to run 4 instances (pods) of >>>>>> Cassandra, you would need 125 servers. >>>>>> Another approach is to build your servers with 5 (or more) SSD >>>>>> devices - one for OS, four for each instance of Cassandra running >>>>>> on that server. Then build some scripts/ansible/puppet that >>>>>> would manage Cassandra start/stops, and other maintenance items. >>>>>> >>>>>> Where I think this runs into problems is with repairs, or >>>>>> sstablescrubs that can take days to run on a single instance. How >>>>>> is that handled 'in the real world'? With seed nodes, how many >>>>>> would you have in such a configuration? >>>>>> Thanks for any thoughts! >>>>>> >>>>>> -Joe >>>>>> >>>>>> >>>> >> -- This email has been checked for viruses by AVG antivirus software. www.avg.com [avg.com]<https://urldefense.com/v3/__http:/www.avg.com__;!!M-nmYVHPHQ!N1mRxPwl0tSfRLfEYnmvAswjcTP4hJoaD3cez01eFBEF_XdWXPbfExCyr_FrSTYe9KCKfOoNiLhaQPjzLbLIEuQ$> ________________________________ The information in this Internet Email is confidential and may be legally privileged. It is intended solely for the addressee. Access to this Email by anyone else is unauthorized. 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