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From Jacques-Henri Berthemet <jacques-henri.berthe...@genesys.com>
Subject RE: LWT on data mutated by non-LWT operation is valid ?
Date Mon, 26 Mar 2018 08:42:51 GMT
If you check the Jira issue I linked you'll see a recent comment describing a potential explanation
for my mixed LWT/non-LWT problem. So, it looks like there can be some edge cases.

I'd say that if data was inserted a while ago (seconds) there should be no problems.

--
Jacques-Henri Berthemet

-----Original Message-----
From: Hiroyuki Yamada [mailto:mogwaing@gmail.com] 
Sent: Sunday, March 25, 2018 1:10 AM
To: user@cassandra.apache.org
Subject: Re: LWT on data mutated by non-LWT operation is valid ?

Thank you JH.
But, it's still a little bit unclear to me

Let me clarify the question.
What I wanted to know is whether or not linearizability is sustained by doing LWT  (Consistency:
QUORUM, Serial Consistency: SERIAL) on data previously mutated by non-LWT (Consistency: QUORUM).
I think It should be OK if non-LWT surely correctly happened before the LWT, but I'm wondering
if there is a corner case where it's not OK.

For example, to test LWT (Update) operations, initial data should be inserted by LWT operations
? or it can be non-LWT operations ?

Thanks,
Hiroyuki

On Sat, Mar 24, 2018 at 8:27 PM, Jacques-Henri Berthemet <jacques-henri.berthemet@genesys.com>
wrote:
> Hi Hiroyuki,
>
>
> For both operations you'll have to provide partition key so "conflict" 
> at DB level can always be resolved.
>
> But if two operations, LWT and non-LWT, are racing against each others 
> the result is unpredictable, if non-LWT is applied after LWT the 
> result will be overwritten.
>
>
> It seems mixing LWT and non-LWT can result in strange results, we 
> recently opened a bug on non-working delete after LWT insert:
> https://issues.apache.org/jira/browse/CASSANDRA-14304
> .apache.org
>
>
> Regards,
>
> JH
>
> ________________________________
> From: Hiroyuki Yamada <mogwaing@gmail.com>
> Sent: Saturday, March 24, 2018 4:38:15 AM
> To: user@cassandra.apache.org
> Subject: LWT on data mutated by non-LWT operation is valid ?
>
> Hi all,
>
> I have some question about LWT.
>
> I am wondering if LWT works only for data mutated by LWT or not.
> In other words, doing LWT on some data mutated by non-LWT operations 
> is still valid ?
> I don't fully understand how system.paxos table works in LWT, but 
> row_key should be empty for a data mutated by non-LWT operation, so 
> conflict resolution seems impossible.
> It works only if a previous non-LWT operation is completely finished ?
>
> Thanks in advance.
>
> Best regards,
> Hiroyuki
>
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