org.apache.spark.util.kvstore.KVIndex Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.spark.util.kvstore;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.apache.spark.annotation.Private;
/**
* 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.
*
*/
@Private
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.METHOD})
public @interface KVIndex {
String NATURAL_INDEX_NAME = "__main__";
/**
* 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).
*/
String value() default NATURAL_INDEX_NAME;
/**
* 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.
*
*/
String parent() default "";
/**
* 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.
*/
boolean copy() default false;
}