Thanks.
It is very helpful.

I think I'd like to write to the same column.

Would you please give me more details about your last sentence? For example, why can't I use locking mechanism inside of cassandra?

Thanks.
Alvin

2010/12/13 Aaron Morton <aaron@thelastpickle.com>
In your example is a little unclear.

 If you are writing to a single row and creating columns with user names. Then when you read all the columns for row 1 you will get columns called Dan and Ken.

If you are writing to the same column, let's say called user, then *if* they are send with the same time stamp the greater value when compared by bytes will be used. Ken in this case.

If you app has sections that are highly concurrent try to design them away, or use a locking mechanism outside of casandra, or use another DB.

Hope that helps.
Aaron


On 14/12/2010, at 7:11 AM, Alvin UW <alvinuw@gmail.com> wrote:

Yes, the same timestamp

2010/12/10 Ryan King <ryan@twitter.com>
On Fri, Dec 10, 2010 at 12:49 PM, Alvin UW <alvinuw@gmail.com> wrote:
> Hello,
>
>
> I got a consistency problem in Cassandra.
>
> Given a column family with a record:    Id   Name
>                                                         1    David
>
> There are three backups for this column family.
>
> Assume there are two write operation happens issued by the same application
> by this order: write_one("1", "Dan") ; write_one("1", "Ken").
> What will Read_all("1") get?
>
> Assume the above two write operations happens exactly the same time in two
> applications,
> Again what will Read_all("1") get?

By "exactly the same" do you mean "with the same timestamp"?

-ryan