Yes, I think I get it now. "quorum of replicas" != "quorum of nodes" and I don't think quorum of nodes is ever defined. Thank you, Konstantin.
Now, I believe I need to change my cluster to store data in two remaining nodes in DC1, keeping 3 nodes in DC2. I believe nodetool removetoken is what I need to use. Anything else I can/should do? On Fri, Sep 2, 2011 at 1:56 PM, Konstantin Naryshkin <konstant...@a-bb.net> wrote: > I think that Oleg may have misunderstood how replicas are selected. If you > have 3 nodes in your cluster and a RF of 2, Cassandra first selects what two > nodes, out of the 3 will get data, then, and only then does it write it out. > The selection is based on the row key, the token of the node, and you choice > of partitioner. This means that Cassandra does not need to store what node is > responsible for a given row. That information can be recalculated whenever it > is needed. > > The error that you are getting is because you may have 2 nodes up, those are > not the nodes that Cassandra will use to store data. > > ----- Original Message ----- > From: "Nate McCall" <n...@datastax.com> > To: hector-us...@googlegroups.com > Cc: "Cassandra Users" <user@cassandra.apache.org> > Sent: Friday, September 2, 2011 4:44:01 PM > Subject: Re: HUnavailableException: : May not be enough replicas present to > handle consistency level. > > In your options, you have configured 2 replicas for each data center: > Options: [DC2:2, DC1:2] > > If one of those replicas is down, then LOCAL_QUORUM will fail as there > is only one replica left 'locally.' > > > On Fri, Sep 2, 2011 at 3:35 PM, Oleg Tsvinev <oleg.tsvi...@gmail.com> wrote: >> from http://www.datastax.com/docs/0.8/consistency/index: >> >> <A “quorum” of replicas is essentially a majority of replicas, or RF / >> 2 + 1 with any resulting fractions rounded down.> >> >> I have RF=2, so majority of replicas is 2/2+1=2 which I have after 3rd >> node goes down? >> >> On Fri, Sep 2, 2011 at 1:22 PM, Nate McCall <n...@datastax.com> wrote: >>> It looks like you only have 2 replicas configured in each data center? >>> >>> If so, LOCAL_QUORUM cannot be achieved with a host down same as with >>> QUORUM on RF=2 in a single DC cluster. >>> >>> On Fri, Sep 2, 2011 at 1:40 PM, Oleg Tsvinev <oleg.tsvi...@gmail.com> wrote: >>>> I believe I don't quite understand semantics of this exception: >>>> >>>> me.prettyprint.hector.api.exceptions.HUnavailableException: : May not >>>> be enough replicas present to handle consistency level. >>>> >>>> Does it mean there *might be* enough? >>>> Does it mean there *is not* enough? >>>> >>>> My case is as following - I have 3 nodes with keyspaces configured as >>>> following: >>>> >>>> Replication Strategy: org.apache.cassandra.locator.NetworkTopologyStrategy >>>> Durable Writes: true >>>> Options: [DC2:2, DC1:2] >>>> >>>> Hector can only connect to nodes in DC1 and configured to neither see >>>> nor connect to nodes in DC2. This is for replication by Cassandra >>>> means, asynchronously between datacenters DC1 and DC2. Each of 6 total >>>> nodes can see any of the remaining 5. >>>> >>>> and inserts with LOCAL_QUORUM CL work fine when all 3 nodes are up. >>>> However, this morning one node went down and I started seeing the >>>> HUnavailableException: : May not be enough replicas present to handle >>>> consistency level. >>>> >>>> I believed if I have 3 nodes and one goes down, two remaining nodes >>>> are sufficient for my configuration. >>>> >>>> Please help me to understand what's going on. >>>> >>> >> >
