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From Bhupesh Chawda <bhup...@datatorrent.com>
Subject Re: [DISCUSS] Proposal for adapting Malhar operators for batch use cases
Date Tue, 28 Feb 2017 10:13:26 GMT
Hi David,

If using time window does not seem appropriate, we can have another class
which is more suited for such sequential and distinct windows. Perhaps, a
CustomWindow option can be introduced which takes in a window id. The
purpose of this window option could be to translate the window id into
appropriate timestamps.

Another option would be to go with a custom timestampExtractor for such
tuples which translates the each unique file name to a distinct timestamp
while using time windows in the windowed operator.

~ Bhupesh


_______________________________________________________

Bhupesh Chawda

E: bhupesh@datatorrent.com | Twitter: @bhupeshsc

www.datatorrent.com  |  apex.apache.org



On Tue, Feb 28, 2017 at 12:28 AM, David Yan <davidyan@gmail.com> wrote:

> I now see your rationale on putting the filename in the window.
> As far as I understand, the reasons why the filename is not part of the key
> and the Global Window is not used are:
>
> 1) The files are processed in sequence, not in parallel
> 2) The windowed operator should not keep the state associated with the file
> when the processing of the file is done
> 3) The trigger should be fired for the file when a file is done processing.
>
> However, if the file is just a sequence has nothing to do with a timestamp,
> assigning a timestamp to a file is not an intuitive thing to do and would
> just create confusions to the users, especially when it's used as an
> example for new users.
>
> How about having a separate class called SequenceWindow? And perhaps
> TimeWindow can inherit from it?
>
> David
>
> On Mon, Feb 27, 2017 at 8:58 AM, Thomas Weise <thw@apache.org> wrote:
>
> > On Mon, Feb 27, 2017 at 8:50 AM, Bhupesh Chawda <bhupesh@datatorrent.com
> >
> > wrote:
> >
> > > I think my comments related to count based windows might be causing
> > > confusion. Let's not discuss count based scenarios for now.
> > >
> > > Just want to make sure we are on the same page wrt. the "each file is a
> > > batch" use case. As mentioned by Thomas, the each tuple from the same
> > file
> > > has the same timestamp (which is just a sequence number) and that helps
> > > keep tuples from each file in a separate window.
> > >
> >
> > Yes, in this case it is a sequence number, but it could be a time stamp
> > also, depending on the file naming convention. And if it was event time
> > processing, the watermark would be derived from records within the file.
> >
> > Agreed, the source should have a mechanism to control the time stamp
> > extraction along with everything else pertaining to the watermark
> > generation.
> >
> >
> > > We could also implement a "timestampExtractor" interface to identify
> the
> > > timestamp (sequence number) for a file.
> > >
> > > ~ Bhupesh
> > >
> > >
> > > _______________________________________________________
> > >
> > > Bhupesh Chawda
> > >
> > > E: bhupesh@datatorrent.com | Twitter: @bhupeshsc
> > >
> > > www.datatorrent.com  |  apex.apache.org
> > >
> > >
> > >
> > > On Mon, Feb 27, 2017 at 9:52 PM, Thomas Weise <thw@apache.org> wrote:
> > >
> > > > I don't think this is a use case for count based window.
> > > >
> > > > We have multiple files that are retrieved in a sequence and there is
> no
> > > > knowledge of the number of records per file. The requirement is to
> > > > aggregate each file separately and emit the aggregate when the file
> is
> > > read
> > > > fully. There is no concept of "end of something" for an individual
> key
> > > and
> > > > global window isn't applicable.
> > > >
> > > > However, as already explained and implemented by Bhupesh, this can be
> > > > solved using watermark and window (in this case the window timestamp
> > > isn't
> > > > a timestamp, but a file sequence, but that doesn't matter.
> > > >
> > > > Thomas
> > > >
> > > >
> > > > On Mon, Feb 27, 2017 at 8:05 AM, David Yan <davidyan@gmail.com>
> wrote:
> > > >
> > > > > I don't think this is the way to go. Global Window only means the
> > > > timestamp
> > > > > does not matter (or that there is no timestamp). It does not
> > > necessarily
> > > > > mean it's a large batch. Unless there is some notion of event time
> > for
> > > > each
> > > > > file, you don't want to embed the file into the window itself.
> > > > >
> > > > > If you want the result broken up by file name, and if the files are
> > to
> > > be
> > > > > processed in parallel, I think making the file name be part of the
> > key
> > > is
> > > > > the way to go. I think it's very confusing if we somehow make the
> > file
> > > to
> > > > > be part of the window.
> > > > >
> > > > > For count-based window, it's not implemented yet and you're welcome
> > to
> > > > add
> > > > > that feature. In case of count-based windows, there would be no
> > notion
> > > of
> > > > > time and you probably only trigger at the end of each window. In
> the
> > > case
> > > > > of count-based windows, the watermark only matters for batch since
> > you
> > > > need
> > > > > a way to know when the batch has ended (if the count is 10, the
> > number
> > > of
> > > > > tuples in the batch is let's say 105, you need a way to end the
> last
> > > > window
> > > > > with 5 tuples).
> > > > >
> > > > > David
> > > > >
> > > > > On Mon, Feb 27, 2017 at 2:41 AM, Bhupesh Chawda <
> > > bhupesh@datatorrent.com
> > > > >
> > > > > wrote:
> > > > >
> > > > > > Hi David,
> > > > > >
> > > > > > Thanks for your comments.
> > > > > >
> > > > > > The wordcount example that I created based on the windowed
> operator
> > > > does
> > > > > > processing of word counts per file (each file as a separate
> batch),
> > > > i.e.
> > > > > > process counts for each file and dump into separate files.
> > > > > > As I understand Global window is for one large batch; i.e. all
> > > incoming
> > > > > > data falls into the same batch. This could not be processed
using
> > > > > > GlobalWindow option as we need more than one windows. In this
> > case, I
> > > > > > configured the windowed operator to have time windows of 1ms
each
> > and
> > > > > > passed data for each file with increasing timestamps: (file1,
1),
> > > > (file2,
> > > > > > 2) and so on. Is there a better way of handling this scenario?
> > > > > >
> > > > > > Regarding (2 - count based windows), I think there is a trigger
> > > option
> > > > to
> > > > > > process count based windows. In case I want to process every
1000
> > > > tuples
> > > > > as
> > > > > > a batch, I could set the Trigger option to CountTrigger with
the
> > > > > > accumulation set to Discarding. Is this correct?
> > > > > >
> > > > > > I agree that (4. Final Watermark) can be done using Global
> window.
> > > > > >
> > > > > > ​~ Bhupesh​
> > > > > >
> > > > > > _______________________________________________________
> > > > > >
> > > > > > Bhupesh Chawda
> > > > > >
> > > > > > E: bhupesh@datatorrent.com | Twitter: @bhupeshsc
> > > > > >
> > > > > > www.datatorrent.com  |  apex.apache.org
> > > > > >
> > > > > >
> > > > > >
> > > > > > On Mon, Feb 27, 2017 at 12:18 PM, David Yan <davidyan@gmail.com>
> > > > wrote:
> > > > > >
> > > > > > > I'm worried that we are making the watermark concept too
> > > complicated.
> > > > > > >
> > > > > > > Watermarks should simply just tell you what windows can
be
> > > considered
> > > > > > > complete.
> > > > > > >
> > > > > > > Point 2 is basically a count-based window. Watermarks do
not
> > play a
> > > > > role
> > > > > > > here because the window is always complete at the n-th
tuple.
> > > > > > >
> > > > > > > If I understand correctly, point 3 is for batch processing
of
> > > files.
> > > > > > Unless
> > > > > > > the files contain timed events, it sounds to be that this
can
> be
> > > > > achieved
> > > > > > > with just a Global Window. For signaling EOF, a watermark
with
> a
> > > > > > +infinity
> > > > > > > timestamp can be used so that triggers will be fired upon
> receipt
> > > of
> > > > > that
> > > > > > > watermark.
> > > > > > >
> > > > > > > For point 4, just like what I mentioned above, can be achieved
> > > with a
> > > > > > > watermark with a +infinity timestamp.
> > > > > > >
> > > > > > > David
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > On Sat, Feb 18, 2017 at 8:04 AM, Bhupesh Chawda <
> > > > > bhupesh@datatorrent.com
> > > > > > >
> > > > > > > wrote:
> > > > > > >
> > > > > > > > Hi Thomas,
> > > > > > > >
> > > > > > > > For an input operator which is supposed to generate
> watermarks
> > > for
> > > > > > > > downstream operators, I can think about the following
> > watermarks
> > > > that
> > > > > > the
> > > > > > > > operator can emit:
> > > > > > > > 1. Time based watermarks (the high watermark / low
watermark)
> > > > > > > > 2. Number of tuple based watermarks (Every n tuples)
> > > > > > > > 3. File based watermarks (Start file, end file)
> > > > > > > > 4. Final watermark
> > > > > > > >
> > > > > > > > File based watermarks seem to be applicable for batch
(file
> > > based)
> > > > as
> > > > > > > well,
> > > > > > > > and hence I thought of looking at these first. Does
this seem
> > to
> > > be
> > > > > in
> > > > > > > line
> > > > > > > > with the thought process?
> > > > > > > >
> > > > > > > > ~ Bhupesh
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > _______________________________________________________
> > > > > > > >
> > > > > > > > Bhupesh Chawda
> > > > > > > >
> > > > > > > > Software Engineer
> > > > > > > >
> > > > > > > > E: bhupesh@datatorrent.com | Twitter: @bhupeshsc
> > > > > > > >
> > > > > > > > www.datatorrent.com  |  apex.apache.org
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > On Thu, Feb 16, 2017 at 10:37 AM, Thomas Weise <
> thw@apache.org
> > >
> > > > > wrote:
> > > > > > > >
> > > > > > > > > I don't think this should be designed based on
a simplistic
> > > file
> > > > > > > > > input-output scenario. It would be good to include
a
> stateful
> > > > > > > > > transformation based on event time.
> > > > > > > > >
> > > > > > > > > More complex pipelines contain stateful transformations
> that
> > > > depend
> > > > > > on
> > > > > > > > > windowing and watermarks. I think we need a watermark
> concept
> > > > that
> > > > > is
> > > > > > > > based
> > > > > > > > > on progress in event time (or other monotonic
increasing
> > > > sequence)
> > > > > > that
> > > > > > > > > other operators can generically work with.
> > > > > > > > >
> > > > > > > > > Note that even file input in many cases can produce
time
> > based
> > > > > > > > watermarks,
> > > > > > > > > for example when you read part files that are
bound by
> event
> > > > time.
> > > > > > > > >
> > > > > > > > > Thanks,
> > > > > > > > > Thomas
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > On Wed, Feb 15, 2017 at 4:02 AM, Bhupesh Chawda
<
> > > > > > > bhupesh@datatorrent.com
> > > > > > > > >
> > > > > > > > > wrote:
> > > > > > > > >
> > > > > > > > > > For better understanding the use case for
control tuples
> in
> > > > > batch,
> > > > > > ​I
> > > > > > > > am
> > > > > > > > > > creating a prototype for a batch application
using File
> > Input
> > > > and
> > > > > > > File
> > > > > > > > > > Output operators.
> > > > > > > > > >
> > > > > > > > > > To enable basic batch processing for File
IO operators, I
> > am
> > > > > > > proposing
> > > > > > > > > the
> > > > > > > > > > following changes to File input and output
operators:
> > > > > > > > > > 1. File Input operator emits a watermark
each time it
> opens
> > > and
> > > > > > > closes
> > > > > > > > a
> > > > > > > > > > file. These can be "start file" and "end
file" watermarks
> > > which
> > > > > > > include
> > > > > > > > > the
> > > > > > > > > > corresponding file names. The "start file"
tuple should
> be
> > > sent
> > > > > > > before
> > > > > > > > > any
> > > > > > > > > > of the data from that file flows.
> > > > > > > > > > 2. File Input operator can be configured
to end the
> > > application
> > > > > > > after a
> > > > > > > > > > single or n scans of the directory (a batch).
This is
> where
> > > the
> > > > > > > > operator
> > > > > > > > > > emits the final watermark (the end of application
control
> > > > tuple).
> > > > > > > This
> > > > > > > > > will
> > > > > > > > > > also shutdown the application.
> > > > > > > > > > 3. The File output operator handles these
control tuples.
> > > > "Start
> > > > > > > file"
> > > > > > > > > > initializes the file name for the incoming
tuples. "End
> > file"
> > > > > > > watermark
> > > > > > > > > > forces a finalize on that file.
> > > > > > > > > >
> > > > > > > > > > The user would be able to enable the operators
to send
> only
> > > > those
> > > > > > > > > > watermarks that are needed in the application.
If none of
> > the
> > > > > > options
> > > > > > > > are
> > > > > > > > > > configured, the operators behave as in a
streaming
> > > application.
> > > > > > > > > >
> > > > > > > > > > There are a few challenges in the implementation
where
> the
> > > > input
> > > > > > > > operator
> > > > > > > > > > is partitioned. In this case, the correlation
between the
> > > > > start/end
> > > > > > > > for a
> > > > > > > > > > file and the data tuples for that file is
lost. Hence we
> > need
> > > > to
> > > > > > > > maintain
> > > > > > > > > > the filename as part of each tuple in the
pipeline.
> > > > > > > > > >
> > > > > > > > > > The "start file" and "end file" control
tuples in this
> > > example
> > > > > are
> > > > > > > > > > temporary names for watermarks. We can have
generic
> "start
> > > > > batch" /
> > > > > > > > "end
> > > > > > > > > > batch" tuples which could be used for other
use cases as
> > > well.
> > > > > The
> > > > > > > > Final
> > > > > > > > > > watermark is common and serves the same
purpose in each
> > case.
> > > > > > > > > >
> > > > > > > > > > Please let me know your thoughts on this.
> > > > > > > > > >
> > > > > > > > > > ~ Bhupesh
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > On Wed, Jan 18, 2017 at 12:22 AM, Bhupesh
Chawda <
> > > > > > > > > bhupesh@datatorrent.com>
> > > > > > > > > > wrote:
> > > > > > > > > >
> > > > > > > > > > > Yes, this can be part of operator configuration.
Given
> > > this,
> > > > > for
> > > > > > a
> > > > > > > > user
> > > > > > > > > > to
> > > > > > > > > > > define a batch application, would mean
configuring the
> > > > > connectors
> > > > > > > > > (mostly
> > > > > > > > > > > the input operator) in the application
for the desired
> > > > > behavior.
> > > > > > > > > > Similarly,
> > > > > > > > > > > there can be other use cases that can
be achieved other
> > > than
> > > > > > batch.
> > > > > > > > > > >
> > > > > > > > > > > We may also need to take care of the
following:
> > > > > > > > > > > 1. Make sure that the watermarks or
control tuples are
> > > > > consistent
> > > > > > > > > across
> > > > > > > > > > > sources. Meaning an HDFS sink should
be able to
> interpret
> > > the
> > > > > > > > watermark
> > > > > > > > > > > tuple sent out by, say, a JDBC source.
> > > > > > > > > > > 2. In addition to I/O connectors, we
should also look
> at
> > > the
> > > > > need
> > > > > > > for
> > > > > > > > > > > processing operators to understand
some of the control
> > > > tuples /
> > > > > > > > > > watermarks.
> > > > > > > > > > > For example, we may want to reset the
operator behavior
> > on
> > > > > > arrival
> > > > > > > of
> > > > > > > > > > some
> > > > > > > > > > > watermark tuple.
> > > > > > > > > > >
> > > > > > > > > > > ~ Bhupesh
> > > > > > > > > > >
> > > > > > > > > > > On Tue, Jan 17, 2017 at 9:59 PM, Thomas
Weise <
> > > > thw@apache.org>
> > > > > > > > wrote:
> > > > > > > > > > >
> > > > > > > > > > >> The HDFS source can operate in
two modes, bounded or
> > > > > unbounded.
> > > > > > If
> > > > > > > > you
> > > > > > > > > > >> scan
> > > > > > > > > > >> only once, then it should emit
the final watermark
> after
> > > it
> > > > is
> > > > > > > done.
> > > > > > > > > > >> Otherwise it would emit watermarks
based on a policy
> > > (files
> > > > > > names
> > > > > > > > > etc.).
> > > > > > > > > > >> The mechanism to generate the marks
may depend on the
> > type
> > > > of
> > > > > > > source
> > > > > > > > > and
> > > > > > > > > > >> the user needs to be able to influence/configure
it.
> > > > > > > > > > >>
> > > > > > > > > > >> Thomas
> > > > > > > > > > >>
> > > > > > > > > > >>
> > > > > > > > > > >> On Tue, Jan 17, 2017 at 5:03 AM,
Bhupesh Chawda <
> > > > > > > > > > bhupesh@datatorrent.com>
> > > > > > > > > > >> wrote:
> > > > > > > > > > >>
> > > > > > > > > > >> > Hi Thomas,
> > > > > > > > > > >> >
> > > > > > > > > > >> > I am not sure that I completely
understand your
> > > > suggestion.
> > > > > > Are
> > > > > > > > you
> > > > > > > > > > >> > suggesting to broaden the
scope of the proposal to
> > treat
> > > > all
> > > > > > > > sources
> > > > > > > > > > as
> > > > > > > > > > >> > bounded as well as unbounded?
> > > > > > > > > > >> >
> > > > > > > > > > >> > In case of Apex, we treat
all sources as unbounded
> > > > sources.
> > > > > > Even
> > > > > > > > > > bounded
> > > > > > > > > > >> > sources like HDFS file source
is treated as
> unbounded
> > by
> > > > > means
> > > > > > > of
> > > > > > > > > > >> scanning
> > > > > > > > > > >> > the input directory repeatedly.
> > > > > > > > > > >> >
> > > > > > > > > > >> > Let's consider HDFS file source
for example:
> > > > > > > > > > >> > In this case, if we treat
it as a bounded source, we
> > can
> > > > > > define
> > > > > > > > > hooks
> > > > > > > > > > >> which
> > > > > > > > > > >> > allows us to detect the end
of the file and send the
> > > > "final
> > > > > > > > > > watermark".
> > > > > > > > > > >> We
> > > > > > > > > > >> > could also consider HDFS file
source as a streaming
> > > source
> > > > > and
> > > > > > > > > define
> > > > > > > > > > >> hooks
> > > > > > > > > > >> > which send watermarks based
on different kinds of
> > > windows.
> > > > > > > > > > >> >
> > > > > > > > > > >> > Please correct me if I misunderstand.
> > > > > > > > > > >> >
> > > > > > > > > > >> > ~ Bhupesh
> > > > > > > > > > >> >
> > > > > > > > > > >> >
> > > > > > > > > > >> > On Mon, Jan 16, 2017 at 9:23
PM, Thomas Weise <
> > > > > thw@apache.org
> > > > > > >
> > > > > > > > > wrote:
> > > > > > > > > > >> >
> > > > > > > > > > >> > > Bhupesh,
> > > > > > > > > > >> > >
> > > > > > > > > > >> > > Please see how that can
be solved in a unified way
> > > using
> > > > > > > windows
> > > > > > > > > and
> > > > > > > > > > >> > > watermarks. It is bounded
data vs. unbounded data.
> > In
> > > > Beam
> > > > > > for
> > > > > > > > > > >> example,
> > > > > > > > > > >> > you
> > > > > > > > > > >> > > can use the "global window"
and the final
> watermark
> > to
> > > > > > > > accomplish
> > > > > > > > > > what
> > > > > > > > > > >> > you
> > > > > > > > > > >> > > are looking for. Batch
is just a special case of
> > > > streaming
> > > > > > > where
> > > > > > > > > the
> > > > > > > > > > >> > source
> > > > > > > > > > >> > > emits the final watermark.
> > > > > > > > > > >> > >
> > > > > > > > > > >> > > Thanks,
> > > > > > > > > > >> > > Thomas
> > > > > > > > > > >> > >
> > > > > > > > > > >> > >
> > > > > > > > > > >> > > On Mon, Jan 16, 2017
at 1:02 AM, Bhupesh Chawda <
> > > > > > > > > > >> bhupesh@datatorrent.com
> > > > > > > > > > >> > >
> > > > > > > > > > >> > > wrote:
> > > > > > > > > > >> > >
> > > > > > > > > > >> > > > Yes, if the user
needs to develop a batch
> > > application,
> > > > > > then
> > > > > > > > > batch
> > > > > > > > > > >> aware
> > > > > > > > > > >> > > > operators need to
be used in the application.
> > > > > > > > > > >> > > > The nature of the
application is mostly
> controlled
> > > by
> > > > > the
> > > > > > > > input
> > > > > > > > > > and
> > > > > > > > > > >> the
> > > > > > > > > > >> > > > output operators
used in the application.
> > > > > > > > > > >> > > >
> > > > > > > > > > >> > > > For example, consider
an application which needs
> > to
> > > > > filter
> > > > > > > > > records
> > > > > > > > > > >> in a
> > > > > > > > > > >> > > > input file and store
the filtered records in
> > another
> > > > > file.
> > > > > > > The
> > > > > > > > > > >> nature
> > > > > > > > > > >> > of
> > > > > > > > > > >> > > > this app is to end
once the entire file is
> > > processed.
> > > > > > > > Following
> > > > > > > > > > >> things
> > > > > > > > > > >> > > are
> > > > > > > > > > >> > > > expected of the
application:
> > > > > > > > > > >> > > >
> > > > > > > > > > >> > > >    1. Once the input
data is over, finalize the
> > > output
> > > > > > file
> > > > > > > > from
> > > > > > > > > > >> .tmp
> > > > > > > > > > >> > > >    files. - Responsibility
of output operator
> > > > > > > > > > >> > > >    2. End the application,
once the data is read
> > and
> > > > > > > > processed -
> > > > > > > > > > >> > > >    Responsibility
of input operator
> > > > > > > > > > >> > > >
> > > > > > > > > > >> > > > These functions
are essential to allow the user
> to
> > > do
> > > > > > higher
> > > > > > > > > level
> > > > > > > > > > >> > > > operations like
scheduling or running a workflow
> > of
> > > > > batch
> > > > > > > > > > >> applications.
> > > > > > > > > > >> > > >
> > > > > > > > > > >> > > > I am not sure about
intermediate (processing)
> > > > operators,
> > > > > > as
> > > > > > > > > there
> > > > > > > > > > >> is no
> > > > > > > > > > >> > > > change in their
functionality for batch use
> cases.
> > > > > > Perhaps,
> > > > > > > > > > allowing
> > > > > > > > > > >> > > > running multiple
batches in a single application
> > may
> > > > > > require
> > > > > > > > > > similar
> > > > > > > > > > >> > > > changes in processing
operators as well.
> > > > > > > > > > >> > > >
> > > > > > > > > > >> > > > ~ Bhupesh
> > > > > > > > > > >> > > >
> > > > > > > > > > >> > > > On Mon, Jan 16,
2017 at 2:19 PM, Priyanka
> Gugale <
> > > > > > > > > > priyag@apache.org
> > > > > > > > > > >> >
> > > > > > > > > > >> > > > wrote:
> > > > > > > > > > >> > > >
> > > > > > > > > > >> > > > > Will it make
an impression on user that, if he
> > > has a
> > > > > > batch
> > > > > > > > > > >> usecase he
> > > > > > > > > > >> > > has
> > > > > > > > > > >> > > > > to use batch
aware operators only? If so, is
> > that
> > > > what
> > > > > > we
> > > > > > > > > > expect?
> > > > > > > > > > >> I
> > > > > > > > > > >> > am
> > > > > > > > > > >> > > > not
> > > > > > > > > > >> > > > > aware of how
do we implement batch scenario so
> > > this
> > > > > > might
> > > > > > > > be a
> > > > > > > > > > >> basic
> > > > > > > > > > >> > > > > question.
> > > > > > > > > > >> > > > >
> > > > > > > > > > >> > > > > -Priyanka
> > > > > > > > > > >> > > > >
> > > > > > > > > > >> > > > > On Mon, Jan
16, 2017 at 12:02 PM, Bhupesh
> > Chawda <
> > > > > > > > > > >> > > > bhupesh@datatorrent.com>
> > > > > > > > > > >> > > > > wrote:
> > > > > > > > > > >> > > > >
> > > > > > > > > > >> > > > > > Hi All,
> > > > > > > > > > >> > > > > >
> > > > > > > > > > >> > > > > > While
design / implementation for custom
> > control
> > > > > > tuples
> > > > > > > is
> > > > > > > > > > >> > ongoing, I
> > > > > > > > > > >> > > > > > thought
it would be a good idea to consider
> > its
> > > > > > > usefulness
> > > > > > > > > in
> > > > > > > > > > >> one
> > > > > > > > > > >> > of
> > > > > > > > > > >> > > > the
> > > > > > > > > > >> > > > > > use cases
-  batch applications.
> > > > > > > > > > >> > > > > >
> > > > > > > > > > >> > > > > > This is
a proposal to adapt / extend
> existing
> > > > > > operators
> > > > > > > in
> > > > > > > > > the
> > > > > > > > > > >> > Apache
> > > > > > > > > > >> > > > > Apex
> > > > > > > > > > >> > > > > > Malhar
library so that it is easy to use
> them
> > in
> > > > > batch
> > > > > > > use
> > > > > > > > > > >> cases.
> > > > > > > > > > >> > > > > > Naturally,
this would be applicable for
> only a
> > > > > subset
> > > > > > of
> > > > > > > > > > >> operators
> > > > > > > > > > >> > > like
> > > > > > > > > > >> > > > > > File,
JDBC and NoSQL databases.
> > > > > > > > > > >> > > > > > For example,
for a file based store, (say
> HDFS
> > > > > store),
> > > > > > > we
> > > > > > > > > > could
> > > > > > > > > > >> > have
> > > > > > > > > > >> > > > > > FileBatchInput
and FileBatchOutput operators
> > > which
> > > > > > allow
> > > > > > > > > easy
> > > > > > > > > > >> > > > integration
> > > > > > > > > > >> > > > > > into a
batch application. These operators
> > would
> > > be
> > > > > > > > extended
> > > > > > > > > > from
> > > > > > > > > > >> > > their
> > > > > > > > > > >> > > > > > existing
implementations and would be "Batch
> > > > Aware",
> > > > > > in
> > > > > > > > that
> > > > > > > > > > >> they
> > > > > > > > > > >> > may
> > > > > > > > > > >> > > > > > understand
the meaning of some specific
> > control
> > > > > tuples
> > > > > > > > that
> > > > > > > > > > flow
> > > > > > > > > > >> > > > through
> > > > > > > > > > >> > > > > > the DAG.
Start batch and end batch seem to
> be
> > > the
> > > > > > > obvious
> > > > > > > > > > >> > candidates
> > > > > > > > > > >> > > > that
> > > > > > > > > > >> > > > > > come to
mind. On receipt of such control
> > tuples,
> > > > > they
> > > > > > > may
> > > > > > > > > try
> > > > > > > > > > to
> > > > > > > > > > >> > > modify
> > > > > > > > > > >> > > > > the
> > > > > > > > > > >> > > > > > behavior
of the operator - to reinitialize
> > some
> > > > > > metrics
> > > > > > > or
> > > > > > > > > > >> finalize
> > > > > > > > > > >> > > an
> > > > > > > > > > >> > > > > > output
file for example.
> > > > > > > > > > >> > > > > >
> > > > > > > > > > >> > > > > > We can
discuss the potential control tuples
> > and
> > > > > > actions
> > > > > > > in
> > > > > > > > > > >> detail,
> > > > > > > > > > >> > > but
> > > > > > > > > > >> > > > > > first
I would like to understand the views
> of
> > > the
> > > > > > > > community
> > > > > > > > > > for
> > > > > > > > > > >> > this
> > > > > > > > > > >> > > > > > proposal.
> > > > > > > > > > >> > > > > >
> > > > > > > > > > >> > > > > > ~ Bhupesh
> > > > > > > > > > >> > > > > >
> > > > > > > > > > >> > > > >
> > > > > > > > > > >> > > >
> > > > > > > > > > >> > >
> > > > > > > > > > >> >
> > > > > > > > > > >>
> > > > > > > > > > >
> > > > > > > > > > >
> > > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

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