I think dynamic schema would be good to consider (schema known and possibly
changing at runtime). Some applications cannot be written under the
assumption that the schema is known upfront.
Also, does this really need to leak into the engine? I think it would be
good to consider alternatives and tradeoffs.
Thomas
On Mon, Jan 30, 2017 at 10:44 PM, Chinmay Kolhatkar <chin...@datatorrent.com
> wrote:
> Consumer of output port operator schema is going next downstream operator.
>
>
> On Tue, Jan 31, 2017 at 4:01 AM, Sergey Golovko <ser...@datatorrent.com>
> wrote:
>
> > Sorry, I’m a new person in the APEX team. And I don't understand clearly
> > who are consumers of the output port operator schema(s).
> >
> > 1. If the consumers are non-run-time callers like the application manager
> > or UI designer, maybe it makes sense to use Java static method(s) to
> > retrieve the output port operator schema(s). I guess the performance of a
> > single call of a static method via reflection can be ignored.
> >
> > 2. If the consumer is next downstream operator, maybe it makes sense to
> > send an output port operator schema from upstream operator to next
> > downstream operator via the stream. The corresponded methods that would
> > send and receive the schema should be declared in the
> > interface/abstract-class of the upstream and downstream operators. The
> > sending/receiving of an output schema should be processed right before
> the
> > sending of the first data record via the stream.
> >
> > One of examples of a typical implementation for sending of metadata with
> a
> > regular result set is the sending of JDBC metadata as a part of JDBC
> result
> > set. And I hope the output schema (metadata of the streamed data) in the
> > implementation should contain not only a signature of the streamed
> objects
> > (like field names and data types), but also any other properties of the
> > data that can be useful by the schema receiver to process the data (for
> > instance, a delimiter for CSV record stream).
> >
> > Thanks,
> > Sergey
> >
> > On 2017-01-25 01:47 (-0800), Chinmay Kolhatkar <chin...@datatorrent.com>
> > wrote:
> > > Thank you all for the feedback.
> > >
> > > I've created a Jira for this: APEXCORE-623 and I'll attach the same
> > > document and link to this mailchain there.
> > >
> > > As a first part of this Jira, there are 2 steps I would like to
> propose:
> > > 1. Add following interface at com.datatorrent.common.util.SchemaAware.
> > >
> > > interface SchemaAware {
> > >
> > > Map<OutputPort, Schema> registerSchema(Map<InputPort, Schema>
> > inputSchema);
> > > }
> > >
> > > This interface can be implemented by Operators to communicate its
> output
> > > schema(s) to engine.
> > > Input to this schema will be schema at its input port.
> > >
> > > 2. After LogicalPlan is created call SchemaAware method from upstream
> to
> > > downstream operator in the DAG to propagate the Schema.
> > >
> > > Once this is done, changes can be done in Malhar for the operators in
> > > question.
> > >
> > > Please share your opinion on this approach.
> > >
> > > Thanks,
> > > Chinmay.
> > >
> > >
> > >
> > >
> > > On Wed, Jan 18, 2017 at 2:31 PM, Priyanka Gugale <pri...@apache.org>
> > wrote:
> > >
> > > > +1 to have this feature.
> > > >
> > > > -Priyanka
> > > >
> > > > On Tue, Jan 17, 2017 at 9:18 PM, Pramod Immaneni <
> > pra...@datatorrent.com>
> > > > wrote:
> > > >
> > > > > +1
> > > > >
> > > > > On Mon, Jan 16, 2017 at 1:23 AM, Chinmay Kolhatkar <
> > chin...@apache.org>
> > > > > wrote:
> > > > >
> > > > > > Hi All,
> > > > > >
> > > > > > Currently a DAG that is generated by user, if contains any
> POJOfied
> > > > > > operators, TUPLE_CLASS attribute needs to be set on each and
> every
> > port
> > > > > > which receives or sends a POJO.
> > > > > >
> > > > > > For e.g., if a DAG is like File -> Parser -> Transform -> Dedup
> ->
> > > > > > Formatter -> Kafka, then TUPLE_CLASS attribute needs to be set by
> > user
> > > > on
> > > > > > both input and output ports of transform, dedup operators and
> also
> > on
> > > > > > parser output and formatter input.
> > > > > >
> > > > > > The proposal here is to reduce work that is required by user to
> > > > configure
> > > > > > the DAG. Technically speaking if an operators knows input schema
> > and
> > > > > > processing properties, it can determine output schema and convey
> > it to
> > > > > > downstream operators. This way the complete pipeline can be
> > configured
> > > > > > without user setting TUPLE_CLASS or even creating POJOs and
> adding
> > them
> > > > > to
> > > > > > classpath.
> > > > > >
> > > > > > On the same idea, I want to propose an approach where the
> pipeline
> > can
> > > > be
> > > > > > configured without user setting TUPLE_CLASS or even creating
> POJOs
> > and
> > > > > > adding them to classpath.
> > > > > > Here is the document which at a high level explains the idea and
> a
> > high
> > > > > > level design:
> > > > > > https://docs.google.com/document/d/1ibLQ1KYCLTeufG7dLoHyN_
> > > > > > tRQXEM3LR-7o_S0z_porQ/edit?usp=sharing
> > > > > >
> > > > > > I would like to get opinion from community about feasibility and
> > > > > > applications of this proposal.
> > > > > > Once we get some consensus we can discuss the design in details.
> > > > > >
> > > > > > Thanks,
> > > > > > Chinmay.
> > > > > >
> > > > >
> > > >
> > >
> >
>
