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From DuyHai Doan <doanduy...@gmail.com>
Subject Re: Understanding the limitation to only one non-PK column in MV-PK
Date Tue, 06 Jun 2017 18:57:47 GMT
All the explanation for why just 1 non PK column can be used as PK for MV
is here:

https://skillsmatter.com/skillscasts/7446-cassandra-udf-and-materialised-views-in-depth

Skip to 19:18 for the explanation

On Mon, May 8, 2017 at 8:08 PM, Fridtjof Sander <
fridtjof.sander@googlemail.com> wrote:

> Hi,
>
> I'm struggling to understand some problems with respect to materialized
> views.
>
> First, I want to understand the example mentioned in
> https://issues.apache.org/jira/browse/CASSANDRA-9928 explaining how
> multiple non-PK columns in the view PK can lead to unrepairable/orphanized
> entries. I understand that only happens if a node dies that pushed an
> "intermediate" state (the result of only one of several updates affecting
> the same entry) to it's view replica. The case mentioned looks like the
> following: initially all nodes have (p=1, a=1, b=1). Then two concurrent
> updates are send: a=2 and b=2. One node gets b=2, deletes view (a=1, b=1,
> p=1) and inserts (a=1, b=2, p=1), then dies. The others get a=1, when is
> why they delete (a=1, b=1, p=1) and insert (a=2, b=1, p=1). Then (a=1,
> b=2, p=1) will never be deleted.
>
> What I don't understand is, why that can never happen with a single
> column. Consider (p=1, a=1) with two updates a=2 and a=3. One node receives
> a=2, deletes view entry (a=1, p=1) and inserts (a=2, p=1), then dies. The
> others get a=3, delete (a=1, p=1) and insert (a=3, p=1). Now, how is (a=2,
> p=1) removed from the view replica that was connected to the dying node? I
> don't get what's different here.
>
> I would really appreciate if someone could share some insight here!
>
> Fridtjof
>

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