spark KVStore 源码
spark KVStore 代码
文件路径:/common/kvstore/src/main/java/org/apache/spark/util/kvstore/KVStore.java
/*
* 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.io.Closeable;
import java.util.Collection;
import org.apache.spark.annotation.Private;
/**
* Abstraction for a local key/value store for storing app data.
*
* <p>
* There are two main features provided by the implementations of this interface:
* </p>
*
* <h3>Serialization</h3>
*
* <p>
* If the underlying data store requires serialization, data will be serialized to and deserialized
* using a {@link KVStoreSerializer}, which can be customized by the application. The serializer is
* based on Jackson, so it supports all the Jackson annotations for controlling the serialization of
* app-defined types.
* </p>
*
* <p>
* Data is also automatically compressed to save disk space.
* </p>
*
* <h3>Automatic Key Management</h3>
*
* <p>
* When using the built-in key management, the implementation will automatically create unique
* keys for each type written to the store. Keys are based on the type name, and always start
* with the "+" prefix character (so that it's easy to use both manual and automatic key
* management APIs without conflicts).
* </p>
*
* <p>
* Another feature of automatic key management is indexing; by annotating fields or methods of
* objects written to the store with {@link KVIndex}, indices are created to sort the data
* by the values of those properties. This makes it possible to provide sorting without having
* to load all instances of those types from the store.
* </p>
*
* <p>
* KVStore instances are thread-safe for both reads and writes.
* </p>
*/
@Private
public interface KVStore extends Closeable {
/**
* Returns app-specific metadata from the store, or null if it's not currently set.
*
* <p>
* The metadata type is application-specific. This is a convenience method so that applications
* don't need to define their own keys for this information.
* </p>
*/
<T> T getMetadata(Class<T> klass) throws Exception;
/**
* Writes the given value in the store metadata key.
*/
void setMetadata(Object value) throws Exception;
/**
* Read a specific instance of an object.
*
* @param naturalKey The object's "natural key", which uniquely identifies it. Null keys
* are not allowed.
* @throws java.util.NoSuchElementException If an element with the given key does not exist.
*/
<T> T read(Class<T> klass, Object naturalKey) throws Exception;
/**
* Writes the given object to the store, including indexed fields. Indices are updated based
* on the annotated fields of the object's class.
*
* <p>
* Writes may be slower when the object already exists in the store, since it will involve
* updating existing indices.
* </p>
*
* @param value The object to write.
*/
void write(Object value) throws Exception;
/**
* Removes an object and all data related to it, like index entries, from the store.
*
* @param type The object's type.
* @param naturalKey The object's "natural key", which uniquely identifies it. Null keys
* are not allowed.
* @throws java.util.NoSuchElementException If an element with the given key does not exist.
*/
void delete(Class<?> type, Object naturalKey) throws Exception;
/**
* Returns a configurable view for iterating over entities of the given type.
*/
<T> KVStoreView<T> view(Class<T> type) throws Exception;
/**
* Returns the number of items of the given type currently in the store.
*/
long count(Class<?> type) throws Exception;
/**
* Returns the number of items of the given type which match the given indexed value.
*/
long count(Class<?> type, String index, Object indexedValue) throws Exception;
/**
* A cheaper way to remove multiple items from the KVStore
*/
<T> boolean removeAllByIndexValues(Class<T> klass, String index, Collection<?> indexValues)
throws Exception;
}
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