Custom data-types

Sean Cribbs sean at basho.com
Fri Aug 29 09:36:18 EDT 2014


Alex,

In short, no, you can't create custom types through schemas. Schemas
currently only refer to Riak Search 2.

We would love that too, but it hasn't happened yet. The problem is not
conceiving of a data type but making its behavior both sensible and
convergent in the face of concurrent activity or network partitions.
For instance, say that two tweets come in around the same time. Who
goes first in the "stack" you described? How can multiple independent
copies reason about which ones to drop from the bottom of the stack to
keep it bounded to 100? What happens if a replica is separated from
the others for a while and has really stale entries, is it valid to
serve those to a user? What happens when one replica pushes an element
and another one pops it at the same time?

These sound like they might be trivial problems, but they are
incredibly hard to reason about in the general case. You have to
reason about the ordering of events, the scope of their effects, and
decide on a least-surprising behavior to expose to the user. Although
we have given a pretty familiar/friendly interface to the data types
shipping in 2.0, their behavior is strictly different from the types
you would use in a single-threaded program in local memory.

On Thu, Aug 28, 2014 at 4:47 PM, Alex De la rosa
<alex.rosa.box at gmail.com> wrote:
> Hi there,
>
> Correct me if I'm wrong, but I think I read somewhere that custom data-types
> can be created through schemas or something like that. So, apart from
> COUNTERS, SETS and MAPS we could have some custom defined ones.
>
> I would love to have a STACKS data-type that would work like a FIFO stack,
> so I could save the last 100 objects for some action. Imagine we are
> building Twitter where millions of tweets are sent all the time, but we want
> to quickly know the last 100 tweets for a user. Imagine something like:
>
> obj.stacks['last_tweets'].add(id_of_last_tweet)
>
> IN: last_tweet ---> STACK_OF_100_TWEETS ---> OUT: older than the 100th goes
> out
>
> Is this possible? If so, how to do it?
>
> Thanks and Best Regards,
> Alex
>
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>



-- 
Sean Cribbs <sean at basho.com>
Software Engineer
Basho Technologies, Inc.
http://basho.com/




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