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From Ufuk Celebi <...@apache.org>
Subject Re: Questions regarding queryable state
Date Thu, 16 Mar 2017 10:20:58 GMT
On Thu, Mar 16, 2017 at 10:00 AM, Kathleen Sharp
<kathleen.sharp@signavio.com> wrote:
> Hi,
>
> I have some questions regarding the Queryable State feature:
>
> Is it possible to use the QueryClient to get a list of keys for a given State?

No, this is not possible at the moment. You would have to trigger a
query for each key and then gather all results (for example via
Future.sequence [1]).

> At the moment it is not possible to use ListState - will this ever be
> introduced?

This is not exposed via the asQueryableState API, because it is not
possible to ever clear the list in that case. You can write a custom
function and create the list state yourself, like this (pseudo code):

stream.keyBy().flatMap({
   ListStateDescriptor<T> listStateDesc = ...
   listStateDesc.setQueryable(name); // make queryable

   ListState state = getRuntimeContext().getListState(listState)
});

I would only use this if the list is also cleared at some point in
time (otherwise it will grow without bounds).

>
> My first impression is that I would need one of these 2 to be able to
> use Queryable state.
>
> I would then probably need to build only top of the queryable state
> client to allow filtering, pagination etc of results. Is the intention
> to enrich the client at some point with this (assuming list state
> becomes supported)?

I can imagine to support querying multiple keys at once, with list
state I'm not sure.

> The queryable state client needs a job id, is there any recommended
> way of getting ahold of this?

No, this is a major shortcoming. :-( I would like to go over the
queryable state client for the next release and make sure to get some
of these annoyances out of the way, like using the job name instead of
the JobID or requiring another query name for the job if you want to
make it queryable via name.

[1] http://www.scala-lang.org/api/current/scala/concurrent/Future$.html#sequence[A,M[X]<:TraversableOnce[X]](in:M[scala.concurrent.Future[A]])(implicitcbf:scala.collection.generic.CanBuildFrom[M[scala.concurrent.Future[A]],A,M[A]],implicitexecutor:scala.concurrent.ExecutionContext):scala.concurrent.Future[M[A]]

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