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From Alvin UW <alvi...@gmail.com>
Subject Re: Consistency question caused by Read_all and Write_one
Date Tue, 14 Dec 2010 16:24:11 GMT
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>ryan@twitter.com>
>
>> On Fri, Dec 10, 2010 at 12:49 PM, Alvin UW < <alvinuw@gmail.com>
>> 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
>>
>
>

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