org.apache.spark.util.kvstore

Annotation Type KVIndex

@Retention(value=RUNTIME)
 @Target(value={FIELD,METHOD})
public @interface KVIndex

Tags a field to be indexed when storing an object.

Types are required to have a natural index that uniquely identifies instances in the store. The default value of the annotation identifies the natural index for the type.

Indexes allow for more efficient sorting of data read from the store. By annotating a field or "getter" method with this annotation, an index will be created that will provide sorting based on the string value of that field.

Note that creating indices means more space will be needed, and maintenance operations like updating or deleting a value will become more expensive.

Indices are restricted to String, integral types (byte, short, int, long, boolean), and arrays of those values.

Field Summary

Fields

Modifier and Type	Fields and Description
static String	NATURAL_INDEX_NAME

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
boolean	copy Whether to copy the instance's data to the index, instead of just storing a pointer to the data.
String	parent The name of the parent index of this index.
String	value The name of the index to be created for the annotated entity.

Field Detail

NATURAL_INDEX_NAME

public static final String NATURAL_INDEX_NAME

Element Detail

value

public abstract String value

The name of the index to be created for the annotated entity. Must be unique within the class. Index names are not allowed to start with an underscore (that's reserved for internal use). The default value is the natural index name (which is always a copy index regardless of the annotation's values).

Default:

"__main__"

parent

public abstract String parent

The name of the parent index of this index. By default there is no parent index, so the generated data can be retrieved without having to provide a parent value.

If a parent index is defined, iterating over the data using the index will require providing a single value for the parent index. This serves as a rudimentary way to provide relationships between entities in the store.

Default:

""

copy

public abstract boolean copy

Whether to copy the instance's data to the index, instead of just storing a pointer to the data. The default behavior is to just store a reference; that saves disk space but is slower to read, since there's a level of indirection.

Default:

false