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> 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> > Sent: Tuesday, December 15, 2020 11:57 AM > To: 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> > > > 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%7Ca5f6a2b17aea4b0f1e6508d8a0f0931a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436302442412850%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=XMZmW3%2BbXmyJaVSDvAWPAe8e2y7ubJw%2BR7p2XBJJXVM%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> > [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> > [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> > [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> > [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> > 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> > 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> > > > From: Benjamin Lerer > <benjamin.le...@datastax.com<mailto:benjamin.le...@datastax.com>> > Date: Tuesday, 15 December 2020 at 11:50 > To: dev@cassandra.apache.org<mailto:dev@cassandra.apache.org> > <dev@cassandra.apache.org<mailto: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>> > 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 For additional commands, e-mail: dev-h...@cassandra.apache.org
