Fair enough, do not hesitate to join us on Slack if you have questions, I bet there are a lot of people willing to gladly answer your questions and concerns about Cassandra and how it differs from your relational world. Nothing bad about a mailing list as such if you prefer it that way, I am just pointing out other channels where one might get answers in a little bit faster manner and target a wider audience.
Stefan On Tue, 15 Dec 2020 at 14:45, Greg Oliver <gol...@microsoft.com.invalid> wrote: > > @Stefan - I'm just exposing my lack of experience with Cassandra and how one > goes about improving perf. In my world (relational), perf can be improved by > spreading queries out to different databases. I saw a presentation where a > Cassandra keyspace was said to be roughly equivalent to a relational database. > > -----Original Message----- > From: Stefan Miklosovic <stefan.mikloso...@instaclustr.com> > Sent: Tuesday, December 15, 2020 1:38 PM > To: dev@cassandra.apache.org > Subject: Re: [EXTERNAL] Re: Triggers > > On Tue, 15 Dec 2020 at 14:24, Greg Oliver <gol...@microsoft.com.invalid> > wrote: > > > > Why not batches: I thought that it might be best that read and write models > > are in different keyspace for perf reasons? As I understand, a batch cannot > > span keyspaces. > > What performance reasons? Do you mean that you want to write into one > keyspace but read it from the second one because of performance, or something > similar? Once you set up your two DCs, to be e.g. on NTS and > 3:3 RF and CL for write is QUORUM or what have you, in order to be faster in > reads you might relax CL to something less demanding, LOCAL_QUOURUM, ONE, > TWO, THREE ... you got the idea. I am just struggling to see how the fact > that you would have multiple keyspaces suddenly enable different queries to > be faster. > > > I've been querying around to see if I can find a "reference implementation" > > of cqrs using Cassandra to see how people recommend manifesting the query > > model(s). No luck so far. > > > > Why trigger? Because according to the docs, a trigger runs atomically with > > the original write. > > > > But - as Benjamin Lerer says below - triggers don't work as expected? Still > > would like to know the right ways and wrong ways to use triggers. Need a > > blog on the topic! > > > > Is materialized view the best way? Can it be in a different keyspace? I > > doubt it - testing. > > > > I originally posted in Cassandra-dev because I'm writing Java code to > > implement the trigger. Didn't know that "dev" means working on > > Cassandra itself. Sorry about that. I'll move the conversation to > > user@ > > > > Thanks very much all for your contributions. > > > > > > -----Original Message----- > > From: Stefan Miklosovic <stefan.mikloso...@instaclustr.com> > > Sent: Tuesday, December 15, 2020 12:59 PM > > To: dev@cassandra.apache.org > > Subject: [EXTERNAL] Re: Triggers > > > > 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://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgith > > ub.com%2Fapache%2Fcassandra%2Fcommit%2F54de771e643e9cc64d1f5dd28b5de8a > > 9a91a219e&data=04%7C01%7Cgolive%40microsoft.com%7C951b740016784762 > > bcfd08d8a0fec1cf%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C63743636 > > 3338858671%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzI > > iLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=WkQo44dXPFH4BdqJjbwjM > > 7mfq0fWE6Ivd70HMOuqnDo%3D&reserved=0 > > 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://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2F > > > > ww > > > > w.slideshare.net%2FDataStax%2Fapache-cassandra-multidatacenter-ess > > > > en > > > > tials-julien-anguenot-iland-internet-solutions-c-summit-2016&d > > > > at > > > > a=04%7C01%7Cgolive%40microsoft.com%7C9de8a9d3369f4934c45508d8a0f93 > > > > cf > > > > 6%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436339671302694% > > > > 7C > > > > Unknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6 > > > > Ik > > > > 1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=AtpoZGyBAOGYrSwHGtC8D7UySR4b > > > > xP > > > > 4pIPwkWB3vytU%3D&reserved=0 > > > > - > > > > https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2F > > > > ww > > > > w.slideshare.net%2FDataStax%2Foperations-consistency-failover-for- > > > > mu > > > > ltidc-clusters-alexander-dejanovski-the-last-pickle-cassandra-summ > > > > it > > > > -2016&data=04%7C01%7Cgolive%40microsoft.com%7C9de8a9d3369f4934 > > > > c4 > > > > 5508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436 > > > > 33 > > > > 9671302694%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2l > > > > uM > > > > zIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=3a5jlc%2BMv6Ick > > > > wJ > > > > CEDLMzurkICg829go%2BTU52HNPiX8%3D&reserved=0 > > > > > > > > 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://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2 > > > >> Fw > > > >> ww.slideshare.net%2Frastrick%2Fpresentation-12982302&data=04% > > > >> 7C > > > >> 01%7Cgolive%40microsoft.com%7C9de8a9d3369f4934c45508d8a0f93cf6%7C > > > >> 72 > > > >> f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436339671302694%7CUnk > > > >> no > > > >> wn%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1h > > > >> aW > > > >> wiLCJXVCI6Mn0%3D%7C1000&sdata=vINBSIM5G2WYkF0RpvYvGadBJ5b8LCi > > > >> gK > > > >> EZsH7s2Ra0%3D&reserved=0< > > > >> https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2 > > > >> Fw > > > >> ww.slideshare.net%2Frastrick%2Fpresentation-12982302&data=04% > > > >> 7C > > > >> 01%7Cgolive%40microsoft.com%7C9de8a9d3369f4934c45508d8a0f93cf6%7C > > > >> 72 > > > >> f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637436339671302694%7CUnk > > > >> no > > > >> wn%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1h > > > >> aW > > > >> wiLCJXVCI6Mn0%3D%7C1000&sdata=vINBSIM5G2WYkF0RpvYvGadBJ5b8LCi > > > >> gK > > > >> EZsH7s2Ra0%3D&reserved=0 > > > >>> > > > >> > > > >> Might help. > > > >> > > > >> Andy > > > >> > > > >> [University of Dundee shield logo]< > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-home&data=04%7C01%7Cgolive%40microsoft.com%7C9d > > > >> e8 > > > >> a9d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7 > > > >> C1 > > > >> %7C0%7C637436339671302694%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjA > > > >> wM > > > >> DAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdat > > > >> a= > > > >> UCsPPZsn00NOQbZtCQQemL8%2BUKrcjR%2BkYbletbFAUTU%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%2F > > > >> uo > > > >> d.ac.uk%2Fsig-fb&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671302694%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> op > > > >> oI%2Fy8MQGUoZUf4JLNSwO0AXvo%2BSPgmlCrMDYqxfVA%3D&reserved=0> > > > >> [University of Dundee Twitter] < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-tw&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671302694%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> Pf UixxwmmdsvAAgIOtFAmvCWBAuyZHHxaDF7a7EI0J8%3D&reserved=0> > > > >> [University of Dundee LinkedIn] < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-li&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671302694%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> 4p kmZtJbfmOhYEUqHVHuNqJ82sKffi55UlNoqRM9iYU%3D&reserved=0> > > > >> [University of Dundee YouTube] < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-yt&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671302694%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> b6 WDU5BQ2MPxdUXMV7svX7GwwoA2o9dxVTaH30SUlWw%3D&reserved=0> > > > >> [University of Dundee Instagram] < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-ig&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671312644%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> xO 3aYY76pRSXudHj0fMwreYc9WE%2BL9WvFUVSOpT3Xr0%3D&reserved=0> > > > >> [University of Dundee Snapchat] < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-sc&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671312644%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> fM > > > >> BdqlVnUrZ8LY8KTe4RfmkWT%2BQqFQ0hkbNN%2F0Cz0s8%3D&reserved=0 > > > >>> > > > >> One of the UK's top 20 universities< > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-strapline&data=04%7C01%7Cgolive%40microsoft.com > > > >> %7 > > > >> C9de8a9d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011d > > > >> b4 > > > >> 7%7C1%7C0%7C637436339671312644%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC > > > >> 4w > > > >> LjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000& > > > >> ;s > > > >> data=%2Fm6vL%2FpEWhutdwcVmEksANunJ71ufHH7BSMleW6vxpM%3D&reser > > > >> ve > > > >> d=0 > > > >>> > > > >> The Guardian University Guide 2021 [Covid code of conduct icons]< > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-cvc&data=04%7C01%7Cgolive%40microsoft.com%7C9de > > > >> 8a > > > >> 9d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C > > > >> 1% > > > >> 7C0%7C637436339671312644%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAw > > > >> MD > > > >> AiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata > > > >> =u > > > >> gYXppAj6idOsHR38kfycILz4TzzUTX3ncPqXIr9HEQ%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%2F > > > >> uo > > > >> d.ac.uk%2Fsig-home&data=04%7C01%7Cgolive%40microsoft.com%7C9d > > > >> e8 > > > >> a9d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7 > > > >> C1 > > > >> %7C0%7C637436339671312644%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjA > > > >> wM > > > >> DAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdat > > > >> a= > > > >> cemMScOW969CviEM%2F8FOddPPREJKdxP5SGIsJEHjAr4%3D&reserved=0 > > > >> < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-home&data=04%7C01%7Cgolive%40microsoft.com%7C9d > > > >> e8 > > > >> a9d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7 > > > >> C1 > > > >> %7C0%7C637436339671312644%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjA > > > >> wM > > > >> DAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdat > > > >> a= > > > >> cemMScOW969CviEM%2F8FOddPPREJKdxP5SGIsJEHjAr4%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%2F > > > >> uo > > > >> d.ac.uk%2Fsig-fb&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671312644%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> my > > > >> 43KF0x8a7Cfw1Mxw89vgzev2V4IE77unYI63GN5%2FM%3D&reserved=0 > > > >> < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-fb&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671312644%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> my > > > >> 43KF0x8a7Cfw1Mxw89vgzev2V4IE77unYI63GN5%2FM%3D&reserved=0>> > > > >> [University of Dundee Twitter] < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-tw&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671312644%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> hS > > > >> 23WW9TkmlvBaHTDLjhRD%2FfIxMfPnBaemqI6g69i1s%3D&reserved=0 > > > >> < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-tw&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671322604%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> mu RPgCkCk9F9BNnTAaZGMFihOoV6Jp9ao9hyOftVhBI%3D&reserved=0>> > > > >> [University of Dundee LinkedIn] < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-li&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671322604%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> g7 > > > >> qWH7kEBgcFAFuOxxnplwbk2EOQoq1bkpL3Y04FJe4%3D&reserved=0 > > > >> < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-li&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671322604%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> g7 qWH7kEBgcFAFuOxxnplwbk2EOQoq1bkpL3Y04FJe4%3D&reserved=0>> > > > >> [University of Dundee YouTube] < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-yt&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671322604%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> vh > > > >> MK%2BRhhGpltjgJE6qsmn4sdyuKPqbiBLfpKOMryQ3o%3D&reserved=0 > > > >> < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-yt&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671322604%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> vh > > > >> MK%2BRhhGpltjgJE6qsmn4sdyuKPqbiBLfpKOMryQ3o%3D&reserved=0>> > > > >> [University of Dundee Instagram] < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-ig&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671322604%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> Jq > > > >> J0aOaMVjlOIHozWuZG0tjC2GX%2BMbC%2Fon2ZSduahEQ%3D&reserved=0 > > > >> < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-ig&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671322604%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> Jq > > > >> J0aOaMVjlOIHozWuZG0tjC2GX%2BMbC%2Fon2ZSduahEQ%3D&reserved=0>> > > > >> [University of Dundee Snapchat] < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-sc&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671322604%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> rw > > > >> i61R76R0b6rciwyDC7xzZDZy3GJDkTET%2BC5Em1KcI%3D&reserved=0 > > > >> < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-sc&data=04%7C01%7Cgolive%40microsoft.com%7C9de8 > > > >> a9 > > > >> d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C1 > > > >> %7 > > > >> C0%7C637436339671332559%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwM > > > >> DA > > > >> iLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata= > > > >> WV > > > >> 2DT5Kwq3VEiw8IMZBlzJ0TNFXnV%2F%2F1puvkaacCjH8%3D&reserved=0 > > > >>>> > > > >>> One of the UK's top 20 universities< > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-strapline&data=04%7C01%7Cgolive%40microsoft.com > > > >> %7 > > > >> C9de8a9d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011d > > > >> b4 > > > >> 7%7C1%7C0%7C637436339671332559%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC > > > >> 4w > > > >> LjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000& > > > >> ;s > > > >> data=J8FCwXqHWyAUzE4fLi1QHAg01nD9amvfAF5IhrYtggc%3D&reserved= > > > >> 0 > > > >> < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-strapline&data=04%7C01%7Cgolive%40microsoft.com > > > >> %7 > > > >> C9de8a9d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011d > > > >> b4 > > > >> 7%7C1%7C0%7C637436339671332559%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC > > > >> 4w > > > >> LjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000& > > > >> ;s > > > >> data=J8FCwXqHWyAUzE4fLi1QHAg01nD9amvfAF5IhrYtggc%3D&reserved= > > > >> 0 > > > >>>> > > > >>> The Guardian University Guide 2021 [Covid code of conduct > > > >>> icons]< > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-cvc&data=04%7C01%7Cgolive%40microsoft.com%7C9de > > > >> 8a > > > >> 9d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C > > > >> 1% > > > >> 7C0%7C637436339671332559%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAw > > > >> MD > > > >> AiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata > > > >> =X > > > >> 8YSo1DfxxYxAmz%2BHGrEPM9ymBKSYLthhK4ZWCUr8Ss%3D&reserved=0 > > > >> < > > > >> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2F > > > >> uo > > > >> d.ac.uk%2Fsig-cvc&data=04%7C01%7Cgolive%40microsoft.com%7C9de > > > >> 8a > > > >> 9d3369f4934c45508d8a0f93cf6%7C72f988bf86f141af91ab2d7cd011db47%7C > > > >> 1% > > > >> 7C0%7C637436339671332559%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAw > > > >> MD > > > >> AiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata > > > >> =X > > > >> 8YSo1DfxxYxAmz%2BHGrEPM9ymBKSYLthhK4ZWCUr8Ss%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. > > > >> in valid% 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 > > > > --------------------------------------------------------------------- > 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
