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Hi Illia,
WEAK/QUORUM instead of true/false it is ok for me.

But we have also STRONG.

What does STRONG mean? In current concept we a using QUORUM and say that it
is strong. I guess it is confusing (at least for me) and can have different
behavior for different backends.

I believe that from user point of view only 4 usecases exist: write and
read with consistency or not.
For example if we use QUORUM for write what is usecase to use read with
STRONG one? QUORUM read is enought to get consistent data. Or if we use
WEAK (ONE) for consistent write what is the use case to use read from
QUORUM? we need to read from ALL.

But we can to use different kinds of backend's abilities to implement
consistent and incosistent operation. To provide the best flexibility of
backend  specific features I propose to use backend specific configuration
section in table schema. In this case you can get much more then in initial
concept. For example specify consistensy level ANY instead of ONE for WEAK
consistency if you want concentrate on performance of TWO if you want to
provide more fault tolerant behavior.

With my proposal we will have only one limitation in comparison with first
proposal - We have maximally flexible consistency, but  per table, not per
request. We have only 2 choices to specify consistensy per request (true or
false). But I believe that it is enough to cover user usecases



On Tue, Apr 29, 2014 at 6:16 AM, Illia Khudoshyn <ikhudoshyn at mirantis.com>wrote:

> Hi all,
>
> Dima, I think I understand your reasoning but I have some issues with
> that. I agree that binary logic is much more straightforward and easy to
> understand and use. But following that logic, having the only one hardcoded
> consistency level is even easier and more understandable.
> As I can see, the idea of the proposal is to provide user a more
> fine-grained control on consistency to leverage backend features AND at the
> same time to not bound ourselves with only this concrete backend's
> features. In scope of Maksym's proposal choice between WEAK/QUORUM for me
> is pretty much the same as your FALSE/TRUE. But I'd prefer to have more.
>
> PS Eager to see your new index design
>
>
> On Tue, Apr 29, 2014 at 7:44 AM, Dmitriy Ukhlov <dukhlov at mirantis.com>wrote:
>
>>
>> Hello Maksym,
>>
>> Thank you for your work!
>>
>> I suggest you to consider more general approach and hide backend specific
>> staff. I have the next proposal:
>> 1) add support for inconsistent write operation by adding PutItem,
>> UpdateItem and DeleteItem request parameters "consistent" = True of False
>> (as well as GetItem and Query requests)
>> 2) add possibility to set backend specific metadata (it would be nice to
>> use some generic format like json) per table in scope of create table
>> request. I suggest to specify mapping for Cassandra consistency level per
>> operation type (consistent read, inconsistent read, consistent write,
>> inconsistent write)
>>
>> I agree that now we have a limitation for inconsistent write operation on
>> tables with indexed fields and for requests with specified expected
>> conditions. I have thought about how to overcome this limitation and it
>> seems that I found out solution for index handling without CAS operation.
>> And maybe it is reasonable to redesign it a bit.
>>
>> On Mon, Apr 28, 2014 at 8:33 AM, MAKSYM IARMAK (CS) <
>> Maksym_Iarmak at symantec.com> wrote:
>>
>>>  Hi,
>>>
>>> Because of we can't use inconsistent write if we use indexed table and
>>> condition operations which indexes based on (this staff requires the state
>>> of data), we have one more issue.
>>>
>>> If we want to make write with consistency level ONE (WEAK) to the
>>> indexed table, we will have 2 variants:
>>> 1. Carry out the operation successfully and implicitly make write to the
>>> indexed table with minimally possible consistency level for it (QUORUM);
>>> 2. Raise an exception, that we can not perform this operation and list
>>> all possible CLs for this operation.
>>>
>>> I personally prefer the 2nd variant. So, does anybody have some
>>> objections or maybe another ideas?
>>>
>>>  ------------------------------
>>> *From:* MAKSYM IARMAK (CS) [Maksym_Iarmak at symantec.com]
>>> *Sent:* Friday, April 25, 2014 9:14 PM
>>> *To:* openstack-dev at lists.openstack.org
>>> *Subject:* [openstack-dev] [MagnetoDB] Configuring consistency draft of
>>> concept
>>>
>>>   >So, here is specification draft of concept.
>>>
>>> _______________________________________________
>>> OpenStack-dev mailing list
>>> OpenStack-dev at lists.openstack.org
>>> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
>>>
>>>
>>
>>
>> --
>> Best regards,
>> Dmitriy Ukhlov
>> Mirantis Inc.
>>
>
>
>
> --
>
> Best regards,
>
> Illia Khudoshyn,
> Software Engineer, Mirantis, Inc.
>
>
>
> 38, Lenina ave. Kharkov, Ukraine
>
> www.mirantis.com <http://www.mirantis.ru/>
>
> www.mirantis.ru
>
>
>
> Skype: gluke_work
>
> ikhudoshyn at mirantis.com
>



-- 
Best regards,
Dmitriy Ukhlov
Mirantis Inc.
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