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Posted to user@cassandra.apache.org by Prabath Abeysekara <pr...@gmail.com> on 2014/06/18 08:08:57 UTC
Minimum Cluster size to accommodate a single node failure
Hi Everyone,
First of all, apologies if the $subject was discussed previously in this
list before. I've already gone through quite a few email trails on this but
still couldn't find a convincing answer which really made me raise this
question again here in this list.
If my understanding is correct, a *3 node Cassandra cluster* would survive
a single node failure while the Replication Factor is set to 3 with
consistency levels are assigned QUORUM for read/write operations. For
example, let's consider the following configuration.
* Number of nodes in the cluster : 3
* Replication Factor : 3
* Read/Write consistencies : QUORUM (this evaluates to 2 when RF is set to
3)
Here's how I expect it to work.
Whenever a read operation takes place, the Cassandra cluster coordinator
node that receives the read request would try to read from at least two
replicas before responding to the client. With Read consistency being 2 (+
all raws being available in all three nodes), we should be able to survive
a single node failure in this particular instance for read operations.
Similarly, for write requests, even in the middle of a single node failure,
the writes should be allowed as the Write consistency is set to 2?
Can someone please confirm whether what's mentioned above is correct?
(Please note that I'm trying to figure out the *minimum* node numbers and I
indeed am aware of the fact that there are other factors also to be
considered in order to come up with the most optimal numbers for a given
cluster requirement).
Cheers,
Prabath
--
Prabath
Re: Minimum Cluster size to accommodate a single node failure
Posted by Robert Coli <rc...@eventbrite.com>.
On Tue, Jun 17, 2014 at 11:08 PM, Prabath Abeysekara <
prabathabeysekara@gmail.com> wrote:
> First of all, apologies if the $subject was discussed previously in this
> list before. I've already gone through quite a few email trails on this but
> still couldn't find a convincing answer which really made me raise this
> question again here in this list.
>
http://mail-archives.apache.org/mod_mbox/cassandra-user/201403.mbox/%3CCAEDUwd1Qt=Laph87Q-UttATcstSojJA7-g6cV76AQNJczP6BVg@mail.gmail.com%3E
and
http://mail-archives.apache.org/mod_mbox/cassandra-user/201404.mbox/%3CCAEDUwd2rhFwVXiByccJ1-VrPOYbDtd0LWGnzpU4CxA2u=MiuZg@mail.gmail.com%3E
tl;dr :
It depends on what you mean by "minimum" and "survive". Most people
consider the "minimum" to use QUORUM to "survive" a single node "failure"
to be RF=N=3. The links elaborate on why that is not exactly correct, but
in many cases, it is correct enough.
=Rob
Re: Minimum Cluster size to accommodate a single node failure
Posted by Ken Hancock <ke...@schange.com>.
Another nice resource...
http://www.ecyrd.com/cassandracalculator/
Re: Minimum Cluster size to accommodate a single node failure
Posted by Ben Bromhead <be...@instaclustr.com>.
Yes your thinking is correct.
This article from TLP sums it all up beautifully http://thelastpickle.com/blog/2011/06/13/Down-For-Me.html
Ben Bromhead
Instaclustr | www.instaclustr.com | @instaclustr | +61 415 936 359
On 18 Jun 2014, at 4:18 pm, Prabath Abeysekara <pr...@gmail.com> wrote:
> Sorry, the title of this thread has to be "Minimum cluster size to survive a single node failure".
>
>
> On Wed, Jun 18, 2014 at 11:38 AM, Prabath Abeysekara <pr...@gmail.com> wrote:
> Hi Everyone,
>
> First of all, apologies if the $subject was discussed previously in this list before. I've already gone through quite a few email trails on this but still couldn't find a convincing answer which really made me raise this question again here in this list.
>
> If my understanding is correct, a 3 node Cassandra cluster would survive a single node failure while the Replication Factor is set to 3 with consistency levels are assigned QUORUM for read/write operations. For example, let's consider the following configuration.
>
> * Number of nodes in the cluster : 3
> * Replication Factor : 3
> * Read/Write consistencies : QUORUM (this evaluates to 2 when RF is set to 3)
>
> Here's how I expect it to work.
>
> Whenever a read operation takes place, the Cassandra cluster coordinator node that receives the read request would try to read from at least two replicas before responding to the client. With Read consistency being 2 (+ all raws being available in all three nodes), we should be able to survive a single node failure in this particular instance for read operations. Similarly, for write requests, even in the middle of a single node failure, the writes should be allowed as the Write consistency is set to 2?
>
> Can someone please confirm whether what's mentioned above is correct?
> (Please note that I'm trying to figure out the minimum node numbers and I indeed am aware of the fact that there are other factors also to be considered in order to come up with the most optimal numbers for a given cluster requirement).
>
>
> Cheers,
> Prabath
> --
> Prabath
>
>
>
> --
> Prabath
Re: Minimum Cluster size to accommodate a single node failure
Posted by Prabath Abeysekara <pr...@gmail.com>.
Sorry, the title of this thread has to be "*Minimum cluster size to survive
a single node failure*".
On Wed, Jun 18, 2014 at 11:38 AM, Prabath Abeysekara <
prabathabeysekara@gmail.com> wrote:
> Hi Everyone,
>
> First of all, apologies if the $subject was discussed previously in this
> list before. I've already gone through quite a few email trails on this but
> still couldn't find a convincing answer which really made me raise this
> question again here in this list.
>
> If my understanding is correct, a *3 node Cassandra cluster* would
> survive a single node failure while the Replication Factor is set to 3 with
> consistency levels are assigned QUORUM for read/write operations. For
> example, let's consider the following configuration.
>
> * Number of nodes in the cluster : 3
> * Replication Factor : 3
> * Read/Write consistencies : QUORUM (this evaluates to 2 when RF is set to
> 3)
>
> Here's how I expect it to work.
>
> Whenever a read operation takes place, the Cassandra cluster coordinator
> node that receives the read request would try to read from at least two
> replicas before responding to the client. With Read consistency being 2 (+
> all raws being available in all three nodes), we should be able to survive
> a single node failure in this particular instance for read operations.
> Similarly, for write requests, even in the middle of a single node failure,
> the writes should be allowed as the Write consistency is set to 2?
>
> Can someone please confirm whether what's mentioned above is correct?
> (Please note that I'm trying to figure out the *minimum* node numbers and
> I indeed am aware of the fact that there are other factors also to be
> considered in order to come up with the most optimal numbers for a given
> cluster requirement).
>
>
> Cheers,
> Prabath
> --
> Prabath
>
--
Prabath