Hi, why can't this be achieved by batches? Do I miss something fundamental here? Batches may write to different tables right ... I am just missing the point of using triggers for this.
I add specifics to Brian's first paragraph, this is covered by CASSANDRA-13985 - https://github.com/apache/cassandra/commit/54de771e643e9cc64d1f5dd28b5de8a9a91a219e This will be firstly introduced in 4.0. Stefan On Tue, 15 Dec 2020 at 13:49, Brian Hess <brianmh...@gmail.com> wrote: > > One challenge to be aware of is that when you use multiple data centers, the > users can make changes in either data center and those changes will propagate > to the other data center. That is, there is no concept of a “read-only data > center” in Cassandra. That may be fine, but some organizations want to grant > access to the data for analytics but don’t want those teams to be able to > modify the original data. You can, in some cases, restrict the write access > through user/role permissions (the analytics team only has read access to > that table), but that may not work depending on your use case (but it usually > does work). > > One comment from Benjamin’s comment below. There is one scenario where the > Trigger could guarantee the data makes it to both tables, specifically if > both tables reside in the same keyspace and have the same partition key(s). > Mutations in the same keyspace on tables that have the same partition key are > internally to Cassandra merged into a single internal Mutation and always > applied atomically. So, if you had an exactly same schema for your second > table and it resides in the same keyspace (mytable and mytable_analytics, > say, both in mykeyspace) your trigger could duplicate the mutation to the > source table to be an exact copy into the second table and Cassandra will > apply these both atomically (they both succeed or they both fail - never just > one). In this scenario, the analytics team could modify data in the second > table and not effect the data in the source table. > > ---->Brian > > > On Dec 15, 2020, at 7:38 AM, pauloricardomg <pauloricard...@gmail.com> > > wrote: > > > > To extend Paul's point, datacenters in cassandra are logical concepts which > > may be useful for your use case and do not necessarily need to be > > represented by physical data centers. > > > > The presentation mentioned by Andrew, while helpful, covers some concepts > > which are specific to Hadoop and may be outdated in more recent versions of > > Cassandra. > > > > I'd recommend two more recent presentations on the multi-DC topic: > > - > > https://www.slideshare.net/DataStax/apache-cassandra-multidatacenter-essentials-julien-anguenot-iland-internet-solutions-c-summit-2016 > > - > > https://www.slideshare.net/DataStax/operations-consistency-failover-for-multidc-clusters-alexander-dejanovski-the-last-pickle-cassandra-summit-2016 > > > > Finally, if you have any more questions on this I'd recommend you send them > > to the u...@cassandra.apache.org mailing list as this mailing list ( > > dev@cassandra.apache.org) is related to the project development of > > Cassandra. > > > >> Em ter., 15 de dez. de 2020 às 09:28, Greg Oliver > >> <gol...@microsoft.com.invalid> escreveu: > >> > >> Can't see it in the email. What's the slide #? > >> > >> From: Andrew Cobley (Staff) <a.e.cob...@dundee.ac.uk> > >> Sent: Tuesday, December 15, 2020 12:26 PM > >> To: dev@cassandra.apache.org > >> Subject: [EXTERNAL] Re: Triggers > >> > >> Yes that's right. I remember this illustration: > >> > >> [Diagram Description automatically generated] > >> > >> > >> From this presentation: > >> > >> https://www.slideshare.net/rastrick/presentation-12982302< > >> https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.slideshare.net%2Frastrick%2Fpresentation-12982302&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031889415%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=itM2Kb7eQqOSPO09fGiuHXJPVjW6C51qXCMYq985WaE%3D&reserved=0 > >>> > >> > >> Might help. > >> > >> Andy > >> > >> [University of Dundee shield logo]< > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-home&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031899372%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=WrafubTszeH9pttSA%2BYVqlfYrcPkTfyIVVZXp7BEq8s%3D&reserved=0 > >>> > >> > >> > >> Andy Cobley > >> Senior Lecturer, Program Director Data Science and Data Engineering MSc > >> School of Science and Engineering, University of Dundee > >> +44 (0)1382 385078 (Not at present) | a.e.cob...@dundee.ac.uk<mailto: > >> a.e.cob...@dundee.ac.uk> > >> [University of Dundee Facebook]< > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-fb&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031899372%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=8IIFStCp5WnED9YVMsPytY0iZghIS%2FZOIKQMKF4cyC4%3D&reserved=0> > >> [University of Dundee Twitter] < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-tw&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031909329%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=6wKLsHnA29J3IAMKab0X65HW6m%2BFxQCTrO9k8ckHUs8%3D&reserved=0> > >> [University of Dundee LinkedIn] < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-li&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031909329%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=ASXnqQm0RhV5syVKZsJRHRgNN1%2B0A02gYGmUD4DMipQ%3D&reserved=0> > >> [University of Dundee YouTube] < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-yt&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031919279%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=IMRJ5gCuQJVWLbB5yRiuaWRUlZaJTN0YXxdmnVeKAMs%3D&reserved=0> > >> [University of Dundee Instagram] < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-ig&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031919279%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=TnfBPZT9hoG%2Fy1xZMvkKHoqGZhsYNv6Ez7kmlTQPctk%3D&reserved=0> > >> [University of Dundee Snapchat] < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-sc&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031919279%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=NRmMMZ2exr%2B8g6kSw%2Bkc75Wi1gwlw4mlqj8NDRlHrMo%3D&reserved=0 > >>> > >> One of the UK's top 20 universities< > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-strapline&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031929244%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=nYLpUf9xI26pOrv44naId%2BIfEtDF41ANCL03O5NQYSw%3D&reserved=0 > >>> > >> The Guardian University Guide 2021 > >> [Covid code of conduct icons]< > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-cvc&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031929244%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=1mHxfAjRPe4632ldow1H4Ov89HLjRi2HxHqwxYDAYOw%3D&reserved=0 > >>> > >> > >> > >> From: Paul Chandler <p...@redshots.com<mailto:p...@redshots.com>> > >> Date: Tuesday, 15 December 2020 at 12:16 > >> To: dev@cassandra.apache.org<mailto:dev@cassandra.apache.org> < > >> dev@cassandra.apache.org<mailto:dev@cassandra.apache.org>> > >> Subject: Re: Triggers > >> Hi Greg, > >> > >> Andy is talking about Cassandra datacenters, which can easily be co > >> located in the same physical datacenter. > >> > >> Paul > >> > >>> On 15 Dec 2020, at 12:10, Greg Oliver <gol...@microsoft.com.INVALID > >> <mailto:gol...@microsoft.com.INVALID>> wrote: > >>> > >>> That's great in theory, but what if your customer is a national > >> government (they require their data to remain within their borders) and > >> there aren't enough DC's in nation to support multiple DC data > >> distribution? > >>> > >>> To get the throughput needed (say - if the government announces a new > >> program and 30M people try to sign up at the same time) CQRS seems a likely > >> part of the solution. > >>> > >>> With Cassandra (and I'm definitely new to it), as I learn more it looks > >> like a set of materialized views might be a way to achieve the goal. > >>> > >>> Thoughts? > >>> > >>> From: Andrew Cobley (Staff) <a.e.cob...@dundee.ac.uk<mailto: > >> a.e.cob...@dundee.ac.uk>> > >>> Sent: Tuesday, December 15, 2020 11:57 AM > >>> To: dev@cassandra.apache.org<mailto:dev@cassandra.apache.org> > >>> Subject: [EXTERNAL] Re: Triggers > >>> > >>> I may be wrong, but isn't the correct pattern for this to use two data > >> centres? You write to one data centre, replicate to the other and read > >> from that one. Or am misunderstanding ? > >>> > >>> Andy > >>> > >>> > >>> [University of Dundee shield logo]< > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-home&data=04%7C01%7Cgolive%40microsoft.com%7Ca5f6a2b17aea4b0f1e6508d8a0f0931a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436302442412850%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=Ixrehte7KrUWOrVJEAEut%2FhQL2E2Ug0aRZbt6nFases%3D&reserved=0 > >> < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-home&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031939190%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=nYMTRgqGct928YpEp0ymbzz5u2qhtvvre3MD461qTN8%3D&reserved=0 > >>>> > >>> > >>> > >>> Andy Cobley > >>> Senior Lecturer, Program Director Data Science and Data Engineering MSc > >>> School of Science and Engineering, University of Dundee > >>> +44 (0)1382 385078 (Not at present) | a.e.cob...@dundee.ac.uk<mailto: > >> a.e.cob...@dundee.ac.uk<mailto:a.e.cob...@dundee.ac.uk% > >> 3cmailto:a.e.cob...@dundee.ac.uk>> > >>> [University of Dundee Facebook]< > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-fb&data=04%7C01%7Cgolive%40microsoft.com%7Ca5f6a2b17aea4b0f1e6508d8a0f0931a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436302442412850%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=XMZmW3%2BbXmyJaVSDvAWPAe8e2y7ubJw%2BR7p2XBJJXVM%3D&reserved=0 > >> < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-fb&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031939190%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=2YHCg6mskJwO73xH6VdVi0%2BYgBh%2Fp5qqvRLTZRQr5k0%3D&reserved=0>> > >> [University of Dundee Twitter] < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-tw&data=04%7C01%7Cgolive%40microsoft.com%7Ca5f6a2b17aea4b0f1e6508d8a0f0931a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436302442422802%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=vrqZgx%2BT1aeT%2FmKcweRupF2FkRlMiOTqcEXjTeLLFIw%3D&reserved=0 > >> < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-tw&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031949151%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=bRUhO%2F%2FcguDgawVDiZKqXIIs7lCpCDBmNQ3bP53tlZs%3D&reserved=0>> > >> [University of Dundee LinkedIn] < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-li&data=04%7C01%7Cgolive%40microsoft.com%7Ca5f6a2b17aea4b0f1e6508d8a0f0931a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436302442422802%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=2mxK7SOrBF3Q%2Bze2a8n8zhPDLFjAoexb%2FFZz2vvn2qk%3D&reserved=0 > >> < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-li&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031949151%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=LMICihjiJ5EmUR30V75tCRqc4X8%2F7%2Byp1MoPftwn2mA%3D&reserved=0>> > >> [University of Dundee YouTube] < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-yt&data=04%7C01%7Cgolive%40microsoft.com%7Ca5f6a2b17aea4b0f1e6508d8a0f0931a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436302442422802%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=AuOTbGCAYIzzylIlraKmZz8aopERMF2mKa%2FONYaTrDU%3D&reserved=0 > >> < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-yt&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031959117%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=jP%2BCHsi2QkUxGgV7nFXvKvhslm6rM4jdxTOH3QUKSfg%3D&reserved=0>> > >> [University of Dundee Instagram] < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-ig&data=04%7C01%7Cgolive%40microsoft.com%7Ca5f6a2b17aea4b0f1e6508d8a0f0931a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436302442432759%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=gc28ZiYUWpTG%2F7knxx65ytSqzNJpAfZW1xSaDUYzaro%3D&reserved=0 > >> < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-ig&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031959117%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=JQMkUXSFB9b7bQRdoMX%2FQTaKT0MOmv6WprbvpWHyx%2Fs%3D&reserved=0>> > >> [University of Dundee Snapchat] < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-sc&data=04%7C01%7Cgolive%40microsoft.com%7Ca5f6a2b17aea4b0f1e6508d8a0f0931a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436302442432759%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=LV5u9t0Bv%2FAfiLpqv%2BQWsl07MTRjuBU8SnyS3QWgqmE%3D&reserved=0 > >> < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-sc&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031969067%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=lHCjH5czLfppqxOwPxy%2BUqszDgE55s4JoBAbERpWJxg%3D&reserved=0 > >>>> > >>> One of the UK's top 20 universities< > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-strapline&data=04%7C01%7Cgolive%40microsoft.com%7Ca5f6a2b17aea4b0f1e6508d8a0f0931a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436302442442719%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=6lbV668OjpYmcQq8hgRXRepJmWCRWfj8xxCVbtJ1fHs%3D&reserved=0 > >> < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-strapline&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031969067%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=dyZz8tMof%2BRYfRTlQZkvaesi0VWizcksMY21uB7c158%3D&reserved=0 > >>>> > >>> The Guardian University Guide 2021 > >>> [Covid code of conduct icons]< > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-cvc&data=04%7C01%7Cgolive%40microsoft.com%7Ca5f6a2b17aea4b0f1e6508d8a0f0931a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436302442442719%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=IuTeD3CgBxfqlULotR8tOx7KsYgZ9s%2Fu3ww4SyMv%2Bfg%3D&reserved=0 > >> < > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fuod.ac.uk%2Fsig-cvc&data=04%7C01%7Cgolive%40microsoft.com%7Cb752cef4803d4deae42b08d8a0f4acd5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436320031979023%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=JGmKjzYxEKUXANjvr2kE06R6hxO3n9lArajgiXsswEg%3D&reserved=0 > >>>> > >>> > >>> > >>> From: Benjamin Lerer <benjamin.le...@datastax.com<mailto: > >> benjamin.le...@datastax.com<mailto:benjamin.le...@datastax.com% > >> 3cmailto:benjamin.le...@datastax.com>>> > >>> Date: Tuesday, 15 December 2020 at 11:50 > >>> To: dev@cassandra.apache.org<mailto:dev@cassandra.apache.org<mailto: > >> dev@cassandra.apache.org%3cmailto:dev@cassandra.apache.org>> < > >> dev@cassandra.apache.org<mailto:dev@cassandra.apache.org<mailto: > >> dev@cassandra.apache.org%3cmailto:dev@cassandra.apache.org>>> > >>> Subject: Re: Triggers > >>> Hi Greg, > >>> > >>> Things are more tricky in an eventually consistent distributed system > >> than > >>> they are in a relational database. Even if the C* triggers were perfect > >>> (and they are not) and your write and read tables were exactly the same, > >>> there is no guarantee that all the updates created by the trigger from > >> the > >>> original mutations will be successfully delivered to your other table and > >>> there are no entropy mechanisms to repair those problems. Overtime the > >> data > >>> in your write and read tables will just start to diverge. > >>> > >>> On Mon, Dec 14, 2020 at 2:02 PM Greg Oliver <gol...@microsoft.com.invalid > >> <mailto:gol...@microsoft.com.invalid<mailto:gol...@microsoft.com.invalid% > >> 3cmailto:gol...@microsoft.com.invalid>>> > >>> wrote: > >>> > >>>> Hi all, > >>>> > >>>> My customer wants to use Cassandra together with the CQRS pattern. This > >> is > >>>> to say, they want to separate reads and writes to different tables, > >>>> potentially in different keyspace or database. > >>>> > >>>> In my experience with relational databases I would set up a trigger on > >> the > >>>> "write" table such that on new row & update row events, a similar row > >> would > >>>> be inserted into the "read" table. > >>>> > >>>> I found a few examples of setting up a trigger on a Cassandra table and > >>>> have replicated that on my system. But in reading the various Stack > >>>> Overflow posts on the topic a persistent message saying "don't do it > >> unless > >>>> you really know what you're doing" pops up. > >>>> > >>>> Why? What are the cases for and against using triggers in Cassandra? > >> What > >>>> are the edge cases to avoid? What is the happy path? > >>>> > >>>> Thanks, > >>>> Greg > >>>> > >>> > >>> The University of Dundee is a registered Scottish Charity, No: SC015096 > >> > >> > >> --------------------------------------------------------------------- > >> To unsubscribe, e-mail: dev-unsubscr...@cassandra.apache.org<mailto: > >> dev-unsubscr...@cassandra.apache.org> > >> For additional commands, e-mail: dev-h...@cassandra.apache.org<mailto: > >> dev-h...@cassandra.apache.org> > >> > >> The University of Dundee is a registered Scottish Charity, No: SC015096 > >> > > --------------------------------------------------------------------- > To unsubscribe, e-mail: dev-unsubscr...@cassandra.apache.org > For additional commands, e-mail: dev-h...@cassandra.apache.org > --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@cassandra.apache.org For additional commands, e-mail: dev-h...@cassandra.apache.org
