@Rakesh: Are you telling a SimpleReplication topology with RF=3 > or NetworkTopology with RF=3.
Just always go with NetworkTopology, I see no reason not doing it nowadays, even on test clusters. If you use SimpleReplicationTopology, all the machines will be considered as only one datacenter, no matters their localisation or configuration which can lead to a lot of issues. C*heers, ----------------------- Alain Rodriguez - al...@thelastpickle.com France The Last Pickle - Apache Cassandra Consulting http://www.thelastpickle.com 2016-03-31 14:03 GMT+02:00 Alain RODRIGUEZ <arodr...@gmail.com>: > Hi, > > Because if you lose a node you have chances to lose some data forever if >> it was not yet replicated. > > > I think I get your point, but keep in mind that CL ONE (or LOCAL_ONE) will > not prevent the coordinator from sending the data to the 2 other replicas, > it will just wait for the first ack, but all the nodes are supposed to have > the write. There are also the hints system, read repairs and repairs. If > none of this work, the problem is probably bigger than just using CL ONE. > > I would advice using QUORUM if a high consistency is important to you. To > spare some space using RF = 2 or to focus at low latency over consistency. > Be carful then, loosing consistency means that returned data might change > depending on the node you hit, if some nodes lose information and entropy > start being high, same query running twice at the same time can return 2 > distinct values depending where they read from. Generally, using RF = 3 and > CL = LOCAL_QUORUM for both reads and writes is the best (safest?) option, > but some people happily run with RF = 2 and CL = LOCAL_ONE. > > we should be able to run with the loss of one DC and loss of at most one >> node in the surviving DC > > > You can parameter that on client side on modern clients using the native > protocol and there are some consistency considerations there too. > > Hope I am correct about all that :-). > > C*heers, > ----------------------- > Alain Rodriguez - al...@thelastpickle.com > France > > The Last Pickle - Apache Cassandra Consulting > http://www.thelastpickle.com > > 2016-03-29 9:56 GMT+02:00 Jacques-Henri Berthemet < > jacques-henri.berthe...@genesys.com>: > >> Because if you lose a node you have chances to lose some data forever if >> it was not yet replicated. >> >> >> >> *--* >> >> *Jacques-Henri Berthemet* >> >> >> >> *From:* Jonathan Haddad [mailto:j...@jonhaddad.com] >> *Sent:* vendredi 25 mars 2016 19:37 >> >> *To:* user@cassandra.apache.org >> *Subject:* Re: How many nodes do we require >> >> >> >> Why would using CL-ONE make your cluster fragile? This isn't obvious to >> me. It's the most practical setting for high availability, which very much >> says "not fragile". >> >> On Fri, Mar 25, 2016 at 10:44 AM Jacques-Henri Berthemet < >> jacques-henri.berthe...@genesys.com> wrote: >> >> I found this calculator very convenient: >> http://www.ecyrd.com/cassandracalculator/ >> >> Regardless of your other DCs you need RF=3 if you write at LOCAL_QUORUM, >> RF=2 if you write/read at ONE. >> >> Obviously using ONE as CL makes your cluster very fragile. >> -- >> Jacques-Henri Berthemet >> >> >> -----Original Message----- >> From: Rakesh Kumar [mailto:rakeshkumar46...@gmail.com] >> Sent: vendredi 25 mars 2016 18:14 >> To: user@cassandra.apache.org >> Subject: Re: How many nodes do we require >> >> On Fri, Mar 25, 2016 at 11:45 AM, Jack Krupansky >> <jack.krupan...@gmail.com> wrote: >> > It depends on how much data you have. A single node can store a lot of >> data, >> > but the more data you have the longer a repair or node replacement will >> > take. How long can you tolerate for a full repair or node replacement? >> >> At this time, for a foreseeable future, size of data will not be >> significant. So we can safely disregard the above as a decision >> factor. >> >> > >> > Generally, RF=3 is both sufficient and recommended. >> >> Are you telling a SimpleReplication topology with RF=3 >> or NetworkTopology with RF=3. >> >> >> taken from: >> >> >> https://docs.datastax.com/en/cassandra/2.0/cassandra/architecture/architectureDataDistributeReplication_c.html >> >> " >> Three replicas in each data center: This configuration tolerates >> either the failure of a one node per replication group at a strong >> consistency level of LOCAL_QUORUM or multiple node failures per data >> center using consistency level ONE." >> >> In our case, with only 3 nodes in each DC, wouldn't a RF=3 effectively >> mean ALL. >> >> I will state our requirement clearly: >> >> If we are going with six nodes (3 in each DC), we should be able to >> write even with a loss of one DC and loss of one node of the surviving >> DC. I am open to hearing what compromise we have to do with the reads >> during the time a DC is down. For us write is critical, more than >> reads. >> >> May be this is not possible with 6 nodes, and requires more. Pls advise. >> >> >
