Cascading 4.0 User Guide - Configuring

1. Introduction: 1.1. What Is Cascading?

1.2. Another Perspective

1.3. Why Use Cascading?

1.4. The Cascading Philosophy

1.5. Who Are the Users?
2. Diving into the APIs: 2.1. Anatomy of a Word-Count Application

2.2. Fluid: An Alternative Fluent API
3. Cascading Basic Concepts: 3.1. Terminology

3.2. Pipe Assemblies

3.3. Pipes

3.4. Platforms

3.5. Sourcing and Sinking Data

3.6. Sink Modes

3.7. Flows
4. Tuple Fields: 4.1. Field Sets

4.2. Field Algebra

4.3. Field Typing

4.4. Type Coercion
5. Pipe Assemblies: 5.1. Each and Every Pipes

5.2. Merge

5.3. GroupBy

5.4. CoGroup

5.5. HashJoin
6. Flows: 6.1. Creating Flows from Pipe Assemblies

6.2. Configuring Flows

6.3. Skipping Flows

6.4. Creating Custom Flows

6.5. Process Levels in the Flow Hierarchy

6.6. Runtime Metrics
7. Cascades: 7.1. Creating a Cascade

7.2. The Cascade Topological Scheduler
8. Configuring: 8.1. Introduction

8.2. Creating Properties

8.3. Passing Properties
9. Local Platform: 9.1. Building an Application

9.2. Executing an Application

9.3. Source and Sink Taps

9.4. Troubleshooting and Debugging
10. The Apache Hadoop Platforms: 10.1. What is Apache Hadoop?

10.2. Hadoop 1 MapReduce vs. Hadoop 2 MapReduce

10.3. Hadoop 2 MapReduce vs Hadoop 2 Tez

10.4. Configuring Applications

10.5. Building an Application

10.6. Executing an Application

10.7. Troubleshooting and Debugging

10.8. Source and Sink Taps

10.9. Custom Taps and Schemes

10.10. Partial Aggregation instead of Combiners

10.11. Custom Types and Serialization
11. Apache Hadoop MapReduce Platform: 11.1. Configuring Applications

11.2. Creating Flows from a JobConf

11.3. Building
12. Apache Tez Platform: 12.1. Configuring Applications

12.2. Building
13. Using and Developing Operations: 13.1. Introduction

13.2. Functions

13.3. Filters

13.4. Aggregators

13.5. Buffers

13.6. Operation and BaseOperation
14. Custom Taps and Schemes: 14.1. Introduction

14.2. Custom Taps

14.3. Custom Schemes

14.4. Taps with File and Nonfile Resources

14.5. Tap Life-Cycle Methods
15. Advanced Processing: 15.1. SubAssemblies

15.2. Stream Assertions

15.3. Failure Traps

15.4. Checkpointing

15.5. Restarting a Checkpointed Flow

15.6. Flow and Cascade Event Handling

15.7. PartitionTaps

15.8. Partial Aggregation instead of Combiners
16. Built-In Operations: 16.1. Identity Function

16.2. Debug Function

16.3. Sample and Limit Functions

16.4. Insert Function

16.5. Text Functions

16.6. Regular Expression Operations

16.7. Java Expression Operations

16.8. XML Operations

16.9. Assertions

16.10. Logical Filter Operators

16.11. Buffers
17. Built-in SubAssemblies: 17.1. Optimized Aggregations

17.2. Stream Shaping
18. Cascading Best Practices: 18.1. Unit Testing

18.2. Flow Granularity

18.3. SubAssemblies, not Factories

18.4. Logical Responsibilities for SubAssemblies

18.5. Java Operators in Field Names

18.6. Debugging Planner Failures

18.7. Optimizing Joins

18.8. Debugging Streams

18.9. Handling Good and Bad Data

18.10. Maintaining State in Operations

18.11. Fields Constants

18.12. Checking the Source Code
19. Extending Cascading: 19.1. Scripting

19.2. Custom Types and Serialization

19.3. Custom Comparators and Hashing
20. Cookbook: Code Examples of Cascading Idioms: 20.1. Tuples and Fields

20.2. Stream Shaping

20.3. Common Operations

20.4. Stream Ordering

20.5. API Usage
21. The Cascading Process Planner: 21.1. FlowConnector

21.2. RuleRegistrySet

21.3. RuleRegistry

21.4. Debugging RuleRegistrySets

Configuring

Introduction

Cascading provides a number of ways to pass properties down for use by built-in or custom operations and integrations, to Cascading internals, or to the underlying platform.

Additionally the scope of the configuration properties can be application-wide, limited to a specific process level (a Flow, a FlowStep, or a FlowNode), or specific to a given Pipe or Tap instance.

Creating Properties

Cascading is very configurable. You can configure aspects of Cascading by creating a property set. Each property consists of a key-value pair. The key is a String value, such as cascading.app.appjar.path. The value is the String path to the "app JAR."

Property sets can be managed directly in a java.util.Properties instance. This class has methods that allow *.property files to be loaded from disk or other locations.

Properties is a subclass of Map<Object,Object>. Any Map type can be used, so long as key-value pairs are stored as type java.util.String.

Properties can be nested via the constructor creating a hierarchy of default key values. But calling getKeySet() and other Map-specific API calls does not return the nested key values. See Properties.getPropertyNames().

Props

All frequently used Cascading properties are encapsulated in subsystem-specific Props subclasses. All Props classes are fluent-style interfaces for creating property sets. For example, the AppProps class can be used for setting application-level configuration settings.

Example 1. Configuring the application JAR

Properties properties = AppProps.appProps()
  .setName( "sample-app" )
  .setVersion( "1.2.3" )
  .addTags( "deploy:prod", "team:engineering" )

  .setJarClass( Main.class ) (1)

    // ALTERNATIVELY ...

  .setJarPath( pathToJar ) (2)

  .buildProperties();

The Props interface allows for both setting available values as well as populating either a Properties or ConfigDef instance for use by Cascading.

There are various "Props-based" classes that expose fluent API calls. The following table lists the most commonly used classes for creating property sets with fluent-style interfaces.

cascading.property.AppProps

Allows for setting application-specific properties. Some properties are required by the underlying platform, like application JAR. Others are simple metadata used by compatible management tools, like tags.

cascading.flow.FlowConnectorProps

Allows for setting a DebugLevel or AssertionLevel for a given FlowConnector to target. Also allows for setting intermediate DecoratorTap subclasses to be used, if any.

cascading.flow.FlowProps

Allows for setting any Flow-specific properties like the maximum concurrent steps to be scheduled, or changing the default Tuple Comparator class.

cascading.flow.FlowRuntimeProps

Allows for setting specific runtime properties, like the level of parallelization to use.

cascading.cascade.CascadeProps

Allows for setting any Cascade-specific properties like the maximum concurrent Flows to be scheduled.

cascading.tap.TrapProps

Allows for fine-grained configuration of what diagnostic data traps should capture on failures.

cascading.tuple.collect.SpillableProps

Allows for fine-grained control over how to manage spilling of data during certain operators that accumulate data. Specifically thresholds and what compression codecs to use.

cascading.pipe.assembly.AggregateByProps

Allows for fine-grained control over the underlying caches used.

Passing Properties

Properties can be applied to the following scopes:

Application: through a default, shared Properties instance
Flow: through a Flow-specific Properties instance passed to the proper FlowConnector
FlowStep: through either Pipe.getStepConfigDef() or Tap.getStepConfigDef()
FlowNode: through either Pipe.getNodeConfigDef() or Tap.getNodeConfigDef()
Pipe: through Pipe.getConfigDef()
Tap: through Tap.getConfigDef()

In the cases of FlowStep and FlowNode, the Pipe and Tap instances that are coded to run on those levels are inspected for property settings. The property settings are merged and, if possible, applied to the underlying configuration for that level.

FlowNode-level properties cannot be applied to the MapReduce platform.

Planner Properties

Properties passed to a FlowConnector are checked by the Cascading query planner. In addition, these properties are pushed directly to the underlying platform as defaults. Any such properties can be overridden by a given scoped ConfigDef instance.

ConfigDef

The ConfigDef class supports the creation of a configuration properties template. The template can then be applied to an existing properties configuration set.

There are three property mode: Mode.DEFAULT, Mode.REPLACE, and Mode.UPDATE.

A DEFAULT property is only applied if there is no existing value in the property set.
A REPLACE property is always applied overriding any previous values.
An UPDATE property is always applied to an existing property, usually when the property key represents a list of values.

The following examples show using the ConfigDef at different scopes.

Example 2. Configuring properties at the FlowStep scope

Pipe join =
  new HashJoin( lhs, common, rhs, common, declared, new InnerJoin() );

SpillableProps props = SpillableProps.spillableProps()
  .setCompressSpill( true )
  .setMapSpillThreshold( 50 * 1000 );

props.setProperties( join.getStepConfigDef(), ConfigDef.Mode.DEFAULT );

Example 3. Configuring properties at the Pipe scope

Pipe join =
  new HashJoin( lhs, common, rhs, common, declared, new InnerJoin() );

SpillableProps props = SpillableProps.spillableProps()
  .setCompressSpill( true )
  .setMapSpillThreshold( 50 * 1000 );

props.setProperties( join.getConfigDef(), ConfigDef.Mode.REPLACE );