Ah thanks a lot for the reply.
The idea for n = 4 is both fault tolerance and performance. Since I have
very few writes, I expect replication IO and view indexing IO to be minimal
and I have no issues with temporary inconsistencies and conflicts.
My understanding is that since there are very few writes, the 4 nodes will
behave almost like 4 independent single nodes and will be able to serve the
read requests independently without having to proxy to cluster peers and
thus avoiding a great deal of extra network and disk IO.
R=3 to me means 3 times the IO and thus 3 machines will be busy for the
same read request instead of serving other requests. Which I understand is
3 times less performance from the cluster as a whole.
If my understanding is correct, I imagine this would be a common use-case
for couch?
On Mon, Mar 11, 2019 at 4:58 PM Robert Newson <rnew...@apache.org> wrote:
> r and w are no longer configurable from the config file by design. The
> default is n/2+1 (so 3 in your case) unless you specify r or w as request
> parameters.
>
> setting n = 4 for a 4 node cluster is very unusual, do you really need 4
> full copies of your data?
>
> couchdb will also automatically lower both r and w if nodes are offline.
>
> The default of n=3, r=w=2 is appropriate in almost all cases as the right
> balance between data safety and availability. Nothing you've said so far
> suggests it would be good to deviate from those settings.
>
> --
> Robert Samuel Newson
> rnew...@apache.org
>
> On Mon, 11 Mar 2019, at 14:52, Vladimir Ralev wrote:
> > Hi all,
> >
> > I am looking into running a 4-node couchdb 2.3 with this config in
> > default.ini and I made sure no other config file override them:
> > [cluster]
> > q = 8
> > n = 4
> > r = 1
> > w = 1
> >
> > But when i create a test DB and check the settings I get:
> > curl -s couch01:5984/mytest1234 |jq . .... .... "cluster": { "q": 8,
> "n": 4,
> > "w": 3, "r": 3 },
> >
> > r and w settings are not respected and seem stuck to be the defaults.
> >
> > When I kill 3 of the machine and test reads and writes, they still work
> > fine so it doesn't seem like the r and w are actually 3 either. I checked
> > if the debug logs printed out the r and w anywhere to confirm what is
> being
> > configured or executed but there is nothing.
> >
> > It is unclear if r and w are active in this version of couch. I can see
> > the
> > they have been partially removed from the documentation
> > https://docs.couchdb.org/en/master/cluster/theory.html as opposed to
> > couchdb 2.0.0 original doc
> >
> https://web.archive.org/web/20160109122310/https://docs.couchdb.org/en/stable/cluster/theory.html
> >
> > Additionally curl -s couch01:5984/mytest1234/doc?r=3
> > still works even if 3 out of the 4 nodes are dead which is unexpected per
> > the quorum documentation here
> > https://docs.couchdb.org/en/master/cluster/sharding.html#quorum
> >
> > My specific concern with r and w is that if r is 3 this means 3 times
> more
> > network and disk IO since it will have to read 3 times from remote
> > machines. My use case really doesn't need this and performance will
> suffer.
> > This is a little hard to test so I was hopinh someone can shed some light
> > on the current situation with r and w in couch 2.3.
> >
> > Thanks
> >
>
