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
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
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 - only N1
to the message?
On Thu, Feb 24, 2011 at 1:40 PM, Anthony John chirayit...@gmail.com
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 works, as this one
...@datastax.comwrote:
On Thu, Feb 24, 2011 at 4:52 PM, Anthony John chirayit...@gmail.comwrote:
Sylvan,
Time stamps are not used for conflict resolution - unless is is part of
the application logic!!!
What is you definition of conflict resolution ? Because if you update twice
the same column
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 sylv...@datastax.comwrote:
On Thu, Feb 24, 2011 at 5:34 PM, Anthony John chirayit...@gmail.comwrote:
Time stamps are not used
).
.
On Thu, Feb 24, 2011 at 11:22 AM, Sylvain Lebresne sylv...@datastax.comwrote:
On Thu, Feb 24, 2011 at 6:01 PM, Anthony John chirayit...@gmail.comwrote:
If you are correct and you are probably closer to the code - then CL of
Quorum does not guarantee
sylv...@datastax.comwrote:
On Thu, Feb 24, 2011 at 6:33 PM, Anthony John chirayit...@gmail.comwrote:
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
of Q read - it depends
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 chirayit...@gmail.com
wrote:
I see the point - apologies for putting everyone through this!
It was just
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
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
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
On Wed, Feb 23, 2011 at 1:57 PM, Anthony John chirayit
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
On Wed, Feb 23, 2011 at 2:48 PM, Anthony John chirayit...@gmail.comwrote:
Ritesh,
At CL ANY - if all endpoints are down - a HH is written
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, that
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
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
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
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 mohitanch...@gmail.com wrote:
I am still trying to understand how writes work. Is there any concept of
sync
and async writes?
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
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,
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.
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 mohitanch...@gmail.com wrote:
Is
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
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
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