All:
So "ANY" CL seems to mean that Write (and read) on any node, even if it is a
hinted handoff, and return success. Correct ?
Guessing this accommodates node failure - right ?
Does "ALL" succeed even if there is a single surviving replica for the
given piece of data ?
Again, tolerates node fa
s better to talk in terms of use cases and if cassandra will be a
> fit for it. Otherwise unless you have W=R=N and fsync before each
> write commit, there will be scope for inconsistency.
>
>
> On Thu, Feb 24, 2011 at 1:25 PM, Anthony John
> wrote:
> > I see the point - ap
0 AM, Sylvain Lebresne wrote:
> On Thu, Feb 24, 2011 at 6:33 PM, Anthony John wrote:
>
>> Completely understand!
>>
>> All that I am quibbling over is whether a CL of quorum guarantees
>> consistency or not. That is what the documentation says - right. IF for a CL
>>
on factor).
.
On Thu, Feb 24, 2011 at 11:22 AM, Sylvain Lebresne wrote:
> On Thu, Feb 24, 2011 at 6:01 PM, Anthony John wrote:
>
>> If you are correct and you are probably closer to the code - then CL of
>> Quorum does not guarantee
If you are correct and you are probably closer to the code - then CL of
Quorum does not guarantee a consistency.
On Thu, Feb 24, 2011 at 10:54 AM, Sylvain Lebresne wrote:
> On Thu, Feb 24, 2011 at 5:34 PM, Anthony John wrote:
>
>> >>Time stamps are not used for conflict reso
b 24, 2011 at 10:12 AM, Sylvain Lebresne wrote:
> On Thu, Feb 24, 2011 at 4:52 PM, Anthony John wrote:
>
>> Sylvan,
>>
>> Time stamps are not used for conflict resolution - unless is is part of
>> the application logic!!!
>>
>
> What is you definition of conf
>
> On Thu, Feb 24, 2011 at 1:40 PM, Anthony John
> wrote:
> > To the list owners - the error text that gmail comes back with is below
> > Now I understand that much of what I write is spam quality, so the mail
> > filter might actually be smart ;).
> > New posts work
>>c. Read with CL = QUORUM. If read hits node1 and node2/node3, new data
that was written to node1 will be returned.
>>In this case - N1 will be identified as a discrepancy and the change will
be discarded via read repair
>>[Naren] How will Cassandra know this is a discrepancy?
Because at Q - on
To the list owners - the error text that gmail comes back with is below
Now I understand that much of what I write is spam quality, so the mail
filter might actually be smart ;).
New posts works, as this one hopefully will. If is on reply that I have a
problem. Any pointers to avoid this situatio
My 2 cents ..
1. Focus should be on the core problem Cassandra is solving i.e.
Availability, Partitioning and a form of consistency that works (in spite of
all the questions) . All this with high performance is a huge step forward -
architecturally!
2. Any enhancement should shore up the core valu
Apologies : For some reason my response on the original mail keeps bouncing
back, thus this new one!
> From the other hand, the same article says:
> "For conditional writes to work, the condition must be evaluated at all
update
> sites before the write can be allowed to succeed."
>
> This means, th
the case of CL ANY. I am talking about the case
>> where your consistency level is R + W > N and you want to write to W nodes
>> but only succeed in writing to X ( where X < W) nodes and hence fail the
>> write to the client.
>>
>> thanks,
>> Ritesh
>>
Tijoriwala <
tijoriwala.rit...@gmail.com> wrote:
> hi Anthony,
> While you stated the facts right, I don't see how it relates to the
> question I ask. Can you elaborate specifically what happens in the case I
> mentioned above to Dave?
>
> thanks,
> Ritesh
>
>
>
Seems to me that the explanations are getting incredibly complicated - while
I submit the real issue is not!
Salient points here:-
1. To be guaranteed data consistency - the writes and reads have to be at
Quorum CL or more
2. Any W/R at lesser CL means that the application has to handle the
incons
Fact as i understand them:-
- A write call to db triggers a number of async writes to all nodes where
the particular write should be recorded (and the nodes are up per Gossip and
so on)
- Once desired CL number of writes acknowledge - the call returns
So your issue is moot. That is what is happeni
This is transparent!
Essentially - when enough writes are acknowledged to meet the desired
Consistency Level - it returns.
On Fri, Feb 18, 2011 at 2:48 PM, mcasandra wrote:
>
> I am still trying to understand how writes work. Is there any concept of
> sync
> and async writes? For eg:
>
> If I w
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
K - let me state the facts first (As I see know them)
- I do not know the inner workings, so interpret my response with that
caveat. Although, at an architectural level, one should be able to keep
detailed implementation at bay
- Quorum is (N+!)/2 where N is the Replication Factor (RF)
- And consis
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
Dave,
I agree with you, mostly ;) !!
While the reference to 2PC is a tad misplaced here - the idea is that the
paradigm of transactions might have to get redefined or - better still -
broadened to include protocols that the provide similar guarantees in an
eventually consistent dispensation.
Bot
Ritesh,
The gist of Dave's contention is that Casandra adds value in spite of the
lack of transactions. However, that need not mean that it can be used for
Enterprise applications. Transaction semantics needs to be re-imagined
within the capabilities of this new kind of database infrastructure, wh
>I am trying to think why R + W > N is said to be consistent and not R + W =
N?
E.g RF of 4 - Write goes to nodes 1/2 and - in R+W=N case - Reads could
happen from 3/4. Does your write could be missed!
HTH,
-JA
On Fri, Feb 11, 2011 at 11:37 AM, mcasandra wrote:
>
> Is commit log file maintai
Some RAID storage might do it, potentially more efficiently!!
Rhetorical question - Does Cassandra's architecture of reconciling reads
over multiple copies of the same data provide an even more interesting
answer? I submit - YES!
All bitrot protection mechanisms involve some element of redundant
>From the architecture section of wiki. And it makes sense!
More specifically: R=read replica count W=write replica count N=replication
factor Q=*QUORUM* (Q = N / 2 + 1)
-
If W + R > N, you will have consistency
- W=1, R=N
- W=N, R=1
- W=Q, R=Q where Q = N / 2 + 1
On Thu, Feb 3,
Not a concern - and here is why:-
>From the wiki arch section captioned below - eventual consistency does not
have to mean inconsistent reads. The concern is the overhead for consistent
reads. But remember in the use case being cited, the expensive read will
happen only during failover, not all th
Look at iostat -x 10 10 when he active par tof your test is running. there
should be something called svc_t - that should be in the 10ms range, and
await should be low.
Will tell you if IO is slow, or if IO is not being issued.
Also, ensure that you ain't swapping with something like "swapon -s"
Sort of - do not agree!!
This is the Shared nothing V/s Shared Disk debate. There are many mainstream
RDBMS products that pretend to do horizontal scalability with Shared Disks.
They have the kinds of problems that Cassandra is specifically architected
to avoid!
The original question here has 2 a
27 matches
Mail list logo
