You're welcomed!
On Thu, Feb 24, 2011 at 5:30 PM, mcasandra wrote:
>
> Thanks. This helps a lot!
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> Sent from the cassandra-u...@incubato
Thanks. This helps a lot!
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No, since you are intentionally asking that at least a QUORUM of the RFs are
written. So in your scenario, only 1 node is up of 3, and QUORUM value is 2.
So that operation will fail, no HH is made.
A read won't succedd either, since you are asking that the data to be
returned must be validated at
Javier Canillas wrote:
>
> HH is some kind of write repair, so it has nothing to do with CL that is a
> requirement of the operation; and it won't be used over reads.
>
> In your example QUORUM is the same as ALL, since you only have 1 RF (only
> the data holder - coordinator). If that node fai
HH is some kind of write repair, so it has nothing to do with CL that is a
requirement of the operation; and it won't be used over reads.
In your example QUORUM is the same as ALL, since you only have 1 RF (only
the data holder - coordinator). If that node fails, all read / writes will
fail.
Now,
On Thu, Feb 24, 2011 at 1:26 PM, mcasandra wrote:
>
> Does HH count towards QUORUM? Say RF=1 and CL of W=QUORUM and one node
> that
> owns the key dies. Would subsequent write operations for that key be
> successful? I am guessing it will not succeed.
>
No, it would not succeed. It would only s
Does HH count towards QUORUM? Say RF=1 and CL of W=QUORUM and one node that
owns the key dies. Would subsequent write operations for that key be
successful? I am guessing it will not succeed.
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Well, it will need all nodes that are required on the operation to be up,
and to response in a timely fashion, even a time-out rpc of 1 replica will
get you a fail response.
CL is calculated based on the RF configured for the ColumnFamily.
"The ConsistencyLevel is an enum that controls both read
Javier Canillas wrote:
>
> Instead, when you execute the same OP using CL QUORUM, then it means
> RF /2+1, it will try to write on the coordinator node and replica.
> Considering only 1 replica is down, the OP will success too.
>
I am assuming even read will succeed when CL QUORUM and RF=3 and
First of all, in your example W=CL?
If it so, then the success of any read / write operarion will be
determine by if the CL required can be satisfied in that moment.
If you write with CL ONE over a CF with RF 3 when 1 node of the
replicas is down, then the operarion will success and HitedHandOff
I am reading this again http://wiki.apache.org/cassandra/HintedHandoff and
got little confused. This is my understanding about how HH should work based
on what I read in Dynamo Paper:
1) Say node A, B, C, D, E are in the cluster in a ring (in that order).
2) For a given key K RF=3.
3) Node B hol
> I read the logic of why writes are not allowed. But other alternative is to
> allow write and just fail the reads until it's in sync again. Is there some
> other problem with this logic?
The problem lies in "until it's in sync again". A given node cannot
easily know for a given read, whether "e
David Strauss-2 wrote:
>
> On Fri, 2011-02-18 at 12:01 -0600, Anthony John wrote:
>> Writes will go thru w/hinted handoff, read will fail
>
> That is not correct. Hinted handoffs do not count toward reaching QUORUM
> counts.[1]
>
> [1] http://wiki.apache.org/cassandra/HintedHandoff
>
> --
>
On Fri, 2011-02-18 at 12:01 -0600, Anthony John wrote:
> Writes will go thru w/hinted handoff, read will fail
That is not correct. Hinted handoffs do not count toward reaching QUORUM
counts.[1]
[1] http://wiki.apache.org/cassandra/HintedHandoff
--
David Strauss
| da...@davidstrauss.net
|
#1, R=2, so if only one machine is up, by definition R cannot be
satisfied. So it will not return.
#2, consistency is an involved topic with no quick and easy
explanation and answers. my 2 cents,
Question of eventual consistency comes in distributed systems, where
you can write to one machine but
Again, my understanding!
1. Writes will go thru w/hinted handoff, read will fail
2. Yes - but Oracle and others have no partition tolerance and lower levels
of availability. To build in partition tolerance and high availability and
still be shared nothing to avoid SPOF (to cover the RAC implementa
I have couple of more quesitons:
1. What happens when RF = 3, R = 2 and W = 2 and 2 machines go down? Would
read and write fail or get the results from that one machine that is up?
2. Someone in this thread mentioned that write is eventually consistent. Is
it because response is returned to the c
On Fri, Feb 18, 2011 at 12:00 AM, Stu Hood wrote:
> But, the reason that it isn't safe to say that we are a strongly consistent
> store is that if 2 of your 3 replicas were to die and come back with no
> data, QUORUM might return the wrong result.
Not so. If you allow vaporizing arbitrary numbe
Related question: Is it a good idea to specify ConsistencyLevels on a
per-operation basis? For example: Read ONE Write ALL would deliver
consistent read results, just like Read ALL Write ONE. However, if you
specify Read ONE Write QUORUM you cannot give such guarantees anymore.
Should there be (is
At Quorum - if 2 of 3 nodes are down, a read should not be returned, right ?
But yes - if single node READs are opted for, it will go through.
The original question was - "Why is Cassandra called eventually consistent
data store?"
Because at write time, there is not a guarantee that all replicas
But, the reason that it isn't safe to say that we are a strongly consistent
store is that if 2 of your 3 replicas were to die and come back with no
data, QUORUM might return the wrong result.
A requirement of a strongly consistent store is that replicas cannot begin
answering queries until they ar
For background...http://wiki.apache.org/cassandra/ArchitectureOverview(There is a section on consistency in there)For deep background...http://www.allthingsdistributed.com/2008/12/eventually_consistent.htmlhttp://s3.amazonaws.com/AllThingsDistributed/sosp/amazon-dynamo-sosp2007.pdfIn short, yes (f
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