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From ibrahim El-sanosi <ibrahimsaba...@gmail.com>
Subject Re: lightweight transactions with potential problem?
Date Wed, 26 Aug 2015 11:19:56 GMT
Thank you lot

Ibrahim

On Wed, Aug 26, 2015 at 12:15 PM, Sylvain Lebresne <sylvain@datastax.com>
wrote:

> Yes
>
> On Wed, Aug 26, 2015 at 1:05 PM, ibrahim El-sanosi <
> ibrahimsabattt@gmail.com> wrote:
>
>> OKKKKKKKKK. I see what the purpose of acknowledgment round here. So
>> acknowledgment is optional here, depend on CL setting as we normally do in
>> Cassandra.
>> So we can say that acknowledgment is not really related to Paxos phase,
>> it depends on CL in Cassandra?
>>
>> Ibrahim
>>
>> On Wed, Aug 26, 2015 at 11:50 AM, Sylvain Lebresne <sylvain@datastax.com>
>> wrote:
>>
>>> On Wed, Aug 26, 2015 at 12:19 PM, ibrahim El-sanosi <
>>> ibrahimsabattt@gmail.com> wrote:
>>>
>>>> Yes, Sylvain, your answer makes more sense. The phase is in Paxos
>>>> protocol sometimes called learning or decide phase, BUT this phase does not
>>>> have acknowledgment round, just learning or decide message from the
>>>> proposer to learners. So why we need acknowledgment round with commit phase
>>>> in lightweight transactions?
>>>>
>>>
>>> It's not _needed_ as far as Paxos is concerned. But it's useful in the
>>> context of Cassandra. The commit phase is about actually persisting to
>>> replica the update decided by the Paxos algorithm and thus making that
>>> update visible to non paxos reads. Being able to apply normal consistencies
>>> to this phase is thus useful, since it allows user to get visibility
>>> guarantees even for non-paxos reads if they so wish, and that's exactly
>>> what we do and why we optionally wait on acknowledgments (and I say
>>> optionally because how many acks we wait on depends on the user provided
>>> consistency level and if that's CL.ANY then the whole Paxos operation
>>> actually return without waiting on any of those acks).
>>>
>>>
>>>
>>
>

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