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From Matt Franklin <m.ben.frank...@gmail.com>
Subject Re: Proposing Changes to the StreamsProvider interface and StreamsProviderTask
Date Tue, 06 May 2014 13:24:19 GMT
On Mon, May 5, 2014 at 1:15 PM, Steve Blackmon <sblackmon@apache.org> wrote:

> What I meant to say re #1 below is that batch-level metadata could be
> useful for modules downstream of the StreamsProvider /
> StreamsPersistReader, and the StreamsResultSet gives us a class to
> which we can add new metadata in core as the project evolves, or
> supplement on a per-module or per-implementation basis via
> subclassing.  Within a provider there's no need to modify or extend
> StreamsResultSet to maintain and utilize state from a third-party API.
>

I agree that in batch mode, metadata might be important.  In conversations
with other people, I think what might be missing is a completely reactive,
event-driven mode where a provider pushes to the rest of the stream rather
than gets polled.


>
> I think I would support making StreamsResultSet an interface rather
> than a class.
>

+1 on interface


>
> Steve Blackmon
> sblackmon@apache.org
>
> On Mon, May 5, 2014 at 12:07 PM, Steve Blackmon <steve@blackmon.org>
> wrote:
> > Comments on this in-line below.
> >
> > On Thu, May 1, 2014 at 4:38 PM, Ryan Ebanks <ryanebanks@gmail.com>
> wrote:
> >> The use and implementations of the StreamsProviders seems to have
> drifted
> >> away from what it was originally designed for.  I recommend that we
> change
> >> the StreamsProvider interface and StreamsProvider task to reflect the
> >> current usage patterns and to be more efficient.
> >>
> >> Current Problems:
> >>
> >> 1.) newPerpetualStream in LocalStream builder is not perpetual.  The
> >> StreamProvider task will shut down after a certain amount of empty
> returns
> >> from the provider.  A perpetual stream implies that it will run in
> >> perpetuity.  If I open a Twitter Gardenhose that is returning tweets
> with
> >> obscure key words, I don't want my stream shutting down if it is just
> quiet
> >> for a few time periods.
> >>
> >> 2.) StreamsProviderTasks assumes that a single read*, will return all
> the
> >> data for that request.  This means that if I do a readRange for a year,
> the
> >> provider has to hold all of that data in memory and return it as one
> >> StreamsResultSet.  I believe the readPerpetual was designed to get
> around
> >> this problem.
> >>
> >> Proposed Fixes/Changes:
> >>
> >> Fix 1.) Remove the StreamsResultSet.  No implementations in the project
> >> currently use it for anything other than a wrapper around a Queue that
> is
> >> then iterated over.  StreamsProvider will now return a
> Queue<StreamsDatum>
> >> instead of a StreamsResultSet.  This will allow providers to queue data
> as
> >> they receive it, and the StreamsProviderTask can pop them off as soon as
> >> they are available.  It will help fix problem #2, as well as help to
> lower
> >> memory usage.
> >>
> >
> > I'm not convinced this is a good idea.  StreamsResultSet is a useful
> > abstraction even if no modules are using it as more than a wrapper for
> > Queue at the moment.  For example read* in a provider or persistReader
> > could return batch-level (as opposed to datum-level) metadata from the
> > underlying API which would be useful state for the provider.
> > Switching to Queue would eliminate our ability to add those
> > capabilities at the core level or at the module level.
> >
> >> Fix 2.) Add a method, public boolean isRunning(), to the StreamsProvider
> >> interface.  The StreamsProviderTask can call this function to see if the
> >> provider is still operating. This will help fix problems #1 and #2. This
> >> will allow the provider to run mulitthreaded, queue data as it's
> available,
> >> and notify the task when it's done so that it can be closed down
> properly.
> >>  It will also allow the stream to be run in perpetuity as the StreamTask
> >> won't shut down providers that have not been producing data for a while.
> >>
> >
> > I think this is a good idea.  +1
> >
> >> Right now the StreamsProvider and StreamsProviderTask seem to be full of
> >> short term fixes that need to be redesigned into long term solutions.
>  With
> >> enough positive feedback, I will create Jira tasks, a feature branch,
> and
> >> begin work.
> >>
> >> Sincerely,
> >> Ryan Ebanks
>

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