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From A J <>
Subject Re: Async write
Date Fri, 18 Feb 2011 21:18:48 GMT
W always stands for number of sync writes. N-W is the number of async writes.
Note, N decides number of replicas. W only decides out of those N
replicas, how many should be written synchronously before returning
success of write to client. All writes always happen to a total of N
nodes (W right away and the rest later)
The higher the value of W the more sync writes and so more latency.

I might be wrong, but I think you cannot decide which of the N nodes
will get the sync write. On a write-by-write basis, I think Cassandra
needs the flexibility to decide on several parameters which W out of N
nodes would it write synchronously.

On Fri, Feb 18, 2011 at 3:48 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 want to have W=2 but 1 write as sync and the 2nd as async.
> Or say I want to have W=3 with networktopology with DC1 getting 1 sync write
> + 1 async write and DC2 always getting async write.
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