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From Ali Akhtar <ali.rac...@gmail.com>
Subject Re: Consistency when adding data to collections concurrently?
Date Sat, 12 Nov 2016 12:08:25 GMT
I am using the Java Cassandra mapper for all of these cases, so my code
looks like this:

Item myItem = myaccessor.get( itemId );
Mapper<Item> mapper = mappingManager.create( Item.class );

myItem.labels.add( newLabel );
mapper.save( myItem );

On Sat, Nov 12, 2016 at 5:06 PM, Ali Akhtar <ali.rac200@gmail.com> wrote:

> Thanks DuyHai, I will switch to using a set.
>
> But I'm still not sure how to resolve the original question.
>
> - Original labels = []
> - Request 1 arrives with label = 1, and request 2 arrives with label = 2
> - Updates are sent to c* with labels = [1] and labels = [2] simultaneously.
>
> What will happen in the above case? Will it cause the labels to end up as
> [1,2] (what I want) or either [1] or [2]?
>
> If I use consistency level = all, will that cause it to end up with [1,2]?
>
> On Sat, Nov 12, 2016 at 4:59 PM, DuyHai Doan <doanduyhai@gmail.com> wrote:
>
>> Don't use list, use set instead. If you need ordering of insertion, use a
>> map<timeuuid,text> where timeuuid is generated by the client to guarantee
>> insertion order
>>
>> When setting a new value to a list, C* will do a read-delete-write
>> internally e.g. read the current list, remove all its value (by a range
>> tombstone) and then write the new list. Please note that prepend & append
>> operations on list do not require this read-delete-write and thus performs
>> slightly better
>>
>> On Sat, Nov 12, 2016 at 11:34 AM, Ali Akhtar <ali.rac200@gmail.com>
>> wrote:
>>
>>> I have a table where each record contains a list<string> of labels.
>>>
>>> I have an endpoint which responds to new labels being added to a record
>>> by the user.
>>>
>>> Consider the following scenario:
>>>
>>> - Record X, labels = []
>>> - User selects 2 labels, clicks a button, and 2 http requests are
>>> generated.
>>> - The server receives request for Label 1 and Label 2 at the same time.
>>> - Both requests see the labels as empty, add 1 label to the collection,
>>> and send it.
>>> - Record state as label 1 request sees it: [1], as label 2 sees it: [2]
>>>
>>> How will the above conflict be resolved? What can I do so I end up with
>>> [1, 2] instead of either [1] or [2] after both requests have been processed?
>>>
>>
>>
>

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