Facets

Note: Make this page's parent CDAP once facets work for both streams and datasets.

Requirements

• CDAP exposes the API for developers to build their own plugin for parsing data in a Stream.

• Developer should have the ability to build his own parser using the CDAP provided API for parsing events in the stream.
• Developer/Operations should then have the ability to deploy the parser implemented into a directory with a configuration
• User should specify at minimum a name and description for the plugin in a configuration
• User should have the ability to list the available plugins using REST API / CLI
• User should have the ability to view using REST API / CLI the pre-defined schema of the plugin in case the plugin defines one.
• User should have the ability to list the views associated with a Stream using REST API / CLI / UI
• User should have the ability to apply the plugin to a Stream and create a view
• User specified view name should be registered in a catalog allowing one to query (SQL) using the view name.
• User should have the ability to apply different plugins on the same Stream creating different view
• User should have the ability to change the plugin associated with a view
• CDAP should provide a text wrangler plugin that allows one to create rules for parsing mostly text files.

Overview

• A facet is another place where data can be read, like streams and datasets.
  
  •  Therefore, facets are readable anywhere a stream or dataset is readable (MapReduce/Spark program, flows, ETL) 
• A facet is a read-only view of a stream or dataset, with a specific read format (schema + format (csv, avro))
• If explore is enabled, then a Hive table will be created for each facet

3.2 Plan

• Facet HTTP API, client, CLI
• Facets can be a view of a stream (not dataset yet)
• Hive tables will be created for facets when explore is enabled

Facet HTTP API

Notes

• If Explore is disabled, then Hive tables will not be created for facets

Sample CLI Flow

1. User wants to create a stream "stream1" that contains CSV data and read using two facets "facet1" and "facet2".
   1. create stream stream1
   2. send stream stream1 "a,b,c"
      send stream stream1 "d,e,f" 

   3. execute "select * from stream_stream1" // may be removed later, as facets already cover this

      body
      a,b,c
      d,e,f

   4. create facet facet1 stream1 format csv "ticker string, num_traded int, price double"

   5. execute "select * from facet_facet1"

      ticker	num_traded	price
      a	b	c
      d	e	f

   6. create facet facet2 stream1 format csv "ticker string, price double" "drop=$2" <-- drop $2 indicates "drop the 2nd field"

   7. execute "select * from facet_facet2"

      ticker	price
      a	c
      d	f