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From Javier Canillas <javier.canil...@gmail.com>
Subject Re: How does Cassandra handle failure during synchronous writes
Date Wed, 23 Feb 2011 14:28:11 GMT
There is something call Hinted Handoff. Suppose that you WRITE something
with ConsistencyLevel.ONE on a cluster defined by 4 nodes. Then, the write
is done on the corresponding node and it is returned an OK to the client,
even if the ReplicationFactor over the destination Keyspace is set to a
higher value.

If in that write, one of the replicated nodes is down, then the coordinator
node (the one that will hold value if first place) will mark that
replication message as not sent and will retry eventually, making the
replication happens.

Please, if I have explained it wrongly correct me.

On Wed, Feb 23, 2011 at 5:45 AM, Aaron Morton <aaron@thelastpickle.com>wrote:

> In the case described below if less than CL nodes respond in rpc_timeout
> (from conf yaml) the client will get a timeout error. I think most higher
> level clients will automatically retry in this case.
>
> If there are not enough nodes to start the request you will get an
> Unavailable exception. Again the client can retry safely.
>
> Aaron
>
>
> On 23/02/2011, at 8:07 PM, Dave Revell <dave@meebo-inc.com> wrote:
>
> Ritesh,
>
> There is no commit protocol. Writes may be persisted on some replicas even
> though the quorum fails. Here's a sequence of events that shows the
> "problem:"
>
> 1. Some replica R fails, but recently, so its failure has not yet been
> detected
> 2. A client writes with consistency > 1
> 3. The write goes to all replicas, all replicas except R persist the write
> to disk
> 4. Replica R never responds
> 5. Failure is returned to the client, but the new value is still in the
> cluster, on all replicas except R.
>
> Something very similar could happen for CL QUORUM.
>
> This is a conscious design decision because a commit protocol would
> constitute tight coupling between nodes, which goes against the Cassandra
> philosophy. But unfortunately you do have to write your app with this case
> in mind.
>
> Best,
> Dave
>
> On Tue, Feb 22, 2011 at 8:22 PM, tijoriwala.ritesh <<tijoriwala.ritesh@gmail.com>
> tijoriwala.ritesh@gmail.com> wrote:
>
>>
>> Hi,
>> I wanted to get details on how does cassandra do synchronous writes to W
>> replicas (out of N)? Does it do a 2PC? If not, how does it deal with
>> failures of of nodes before it gets to write to W replicas? If the
>> orchestrating node cannot write to W nodes successfully, I guess it will
>> fail the write operation but what happens to the completed writes on X (W
>> >
>> X) nodes?
>>
>> Thanks,
>> Ritesh
>> --
>> View this message in context:
>> <http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/How-does-Cassandra-handle-failure-during-synchronous-writes-tp6055152p6055152.html>
>> http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/How-does-Cassandra-handle-failure-during-synchronous-writes-tp6055152p6055152.html
>> Sent from the <cassandra-user@incubator.apache.org>
>> cassandra-user@incubator.apache.org mailing list archive at Nabble.com.
>>
>
>

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