There are two distinct meanings for the term DC - physical data center and workload isolation. I presume the former was intended here. In any case, replication is valid for both physically separate data centers and within a single data center. The latter being useful when a single server machine goes down, either because of a hardware (or software) failure, or to perform maintenance. Having three nodes in a single DC is a normal thing and essential for HA. Granted for more sophisticated operations you want the extra HA of multiple physical data centers, but even if you feel only the need for a single physical data center, HA should still be a valid concern for always-on applications. As a user, I always get really annoyed when a web site says "Sorry, but are systems will be down for maintenance from 12 AM to 3 AM." That's how we can tell that not everybody is using Cassandra (properly.)
-- Jack Krupansky On Wed, Apr 6, 2016 at 10:30 AM, Paco Trujillo <f.truji...@genetwister.nl> wrote: > The fact that there is one single DC does not mean that you do not need > multiples nodes. Without multiples nodes you do not have redundancy (the > nodes fail and you lose the database) and you cannot scale the cluster if > the number of users and/or rows grows adding more nodes unless you have > tested that your query model is correct > > > > *From:* Bhupendra Baraiya [mailto:bhupendra.bara...@continuum.net] > *Sent:* woensdag 6 april 2016 16:15 > *To:* user@cassandra.apache.org > *Subject:* RE: Cassandra Single Node Setup Questions > > > > We have around 20 Million rows and around 200 concurrent users > > > > The reason we want single Node is we have only single DC , I believe if > there is only one DC there is no question of keeping multiple nodes > > > > The main reason we want to migrate to Cassandra is we have a denormalized > data structure in Ms Sql server Database and we want to move to Open source > database , currently we are in process of POC of Cassandra only > > > > I want to keep it less complicated and simple hence I want to go with > Single Node > > > > The main issue that we have is the Transaction support > > > > > > > > > > > > Thanks and regards, > > > > *Bhupendra Baraiya* > > Continuum Managed Services, LLC. > > p: 902-933-0019 > > e: bhupendra.bara...@continuum.net > > w: continuum.net > > [image: > http://cdn2.hubspot.net/hub/281750/file-393087232-png/img/logos/email-continuum-logo-151x26.png] > <http://www.continuum.net/> > > > > *From:* Jack Krupansky [mailto:jack.krupan...@gmail.com > <jack.krupan...@gmail.com>] > *Sent:* April 06, 2016 7:29 PM > *To:* user@cassandra.apache.org > *Subject:* Re: Cassandra Single Node Setup Questions > > > > Generally, regardless of your expected cluster size, you need to perform a > proof of concept implementation (POC) to obtain those numbers for your own > application. These numbers are not absolute limits enforced by Cassandra, > but practical limits based on your actual data model, actual data patterns, > and actual access patterns, as well as your actual hardware - RAM, storage > (SSD vs. HDD), and network connectivity. And queries drive the data > modeling - how do you intend to access the data, latency requirements, and > how many concurrent clients do you expect. > > > > Generally, Cassandra is chosen for applications which have a lot of data > and the need for high availability (redundancy, meaning at least three > copies of the data.) Neither of which seems to be your requirement. > > > > How much data do you have? What led you to believe that you only need a > single node? > > > > > -- Jack Krupansky > > > > On Wed, Apr 6, 2016 at 9:44 AM, Bhupendra Baraiya < > bhupendra.bara...@continuum.net> wrote: > > Hi , > > > > I had few question related to Single Node Setup in Cassandra > > > > 1) We want to install Cassandra but multiple Node is not what we > need > > Can we proceed with Single Node and store millions of data in > Single Node only > > > > 2) How many Partitions are allowed per Node , that is what is the > limit of Partition in single node if exceeded will impact the Performance > > > > 3) How many rows allowed per Partition in Single Node > > > > Thanks and regards, > > > > *Bhupendra Baraiya* > > Continuum Managed Services, LLC. > > p: 902-933-0019 > > e: bhupendra.bara...@continuum.net > > w: continuum.net > > [image: > http://cdn2.hubspot.net/hub/281750/file-393087232-png/img/logos/email-continuum-logo-151x26.png] > <http://www.continuum.net/> > > > > > > >
