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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 14:58:40 GMT
Changing the double quotes to single quotes gives:

UPDATE my_table SET labels = labels + {id: 'foo'} where id = '';

InvalidRequest: Error from server: code=2200 [Invalid query]
message="Invalid user type literal for labels of type list<frozen<label>>"


On Sat, Nov 12, 2016 at 7:50 PM, Ali Akhtar <ali.rac200@gmail.com> wrote:

> The question is about appending to a set of frozen<udt> and how to do that
> while avoiding the race condition.
>
> If I run:
>
>  UPDATE my_table SET labels = labels + {id: "foo"} where id = 'xx';
>
> I get:
>
> SyntaxException: line 1:57 no viable alternative at input '}' (...= labels
> + {id: ["fo]o"}...)
>
> Here labels is set<frozen<label>>
>
> On Sat, Nov 12, 2016 at 7:40 PM, Vladimir Yudovin <vladyu@winguzone.com>
> wrote:
>
>> If I used consistency = ALL both when getting the record, and when saving
>> the record, will that avoid the race condition?
>> If I use consistency level = all, will that cause it to end up with [1,2]?
>> No. Even if you have only one host it's possible that two threads first
>> both read data and than overwrite existing value one by one.
>>
>> The list is actually of a list<frozen<my_udt>> and not a text (I used
>> text for simplification, apologies).
>> In that case, will updates still merge the list values instead of
>> overwriting them?
>> Do you mean UPDATE cql operation? Yes, it adds new values to list,
>> allowing duplicates.
>>
>> 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.
>> As I mentioned duplicates are allowed in LIST, and as DOC says:
>>
>> These update operations are implemented internally without any
>> read-before-write. Appending and prepending a new element to the list
>> writes only the new element.
>>
>> Only when using index
>>
>> When you add an element at a particular position, Cassandra reads the
>> entire list, and then writes only the updated element. Consequently, adding
>> an element at a particular position results in greater latency than
>> appending or prefixing an element to a list.
>>
>>
>> Best regards, Vladimir Yudovin,
>>
>> *Winguzone <https://winguzone.com?from=list> - Hosted Cloud
>> CassandraLaunch your cluster in minutes.*
>>
>>
>> ---- On Sat, 12 Nov 2016 07:57:36 -0500*Ali Akhtar <ali.rac200@gmail.com
>> <ali.rac200@gmail.com>>* wrote ----
>>
>> The labels collection is of the type set<frozen<label>> , where label
is
>> a udt containing: id, name, description , all text fields.
>>
>> On Sat, Nov 12, 2016 at 5:54 PM, Ali Akhtar <ali.rac200@gmail.com> wrote:
>>
>> The problem isn't just the update / insert though, right? Don't frozen
>> entities get overwritten completely? So if I had [1] [2] being written as
>> updates, won't each update overwrite the set completely, so i'll end up
>> with either one of them instead of [1,2]?
>>
>> On Sat, Nov 12, 2016 at 5:50 PM, DuyHai Doan <doanduyhai@gmail.com>
>> wrote:
>>
>> Maybe you should use my Achilles mapper, which does generates UPDATE
>> statements on collections and not only INSERT
>> Le 12 nov. 2016 13:08, "Ali Akhtar" <ali.rac200@gmail.com> a écrit :
>>
>> 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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