ibuenros commented on a change in pull request #2568: [GOBBLIN-697] Implementation of data file versioning and preservation in distcp. URL: https://github.com/apache/incubator-gobblin/pull/2568#discussion_r263622734
########## File path: gobblin-utility/src/main/java/org/apache/gobblin/util/filesystem/DataFileVersion.java ########## @@ -0,0 +1,127 @@ +/* + * 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.gobblin.util.filesystem; + +import com.typesafe.config.Config; +import java.io.IOException; +import java.io.Serializable; +import java.util.Set; + +import org.apache.gobblin.util.ClassAliasResolver; +import org.apache.gobblin.util.ConfigUtils; +import org.apache.hadoop.fs.FileSystem; +import org.apache.hadoop.fs.Path; + + +/** + * An interface to set and get "versions" to data files. + * + * The version is a rough signature to the data contents. It allows data preserving functionality (like copy) to replicate + * the version independently of metadata with other semantics like file modification time. + * + * Examples where this might be useful is data syncing between two locations. Relying on modification times to detect + * data changes may lead to a feedback loop of copying: data gets created at location A at time 0, + * at time 1 data is copied to location B, sync mechanism might incorrectly believe that since mod time of location B + * is higher, it should be synced back to location A, etc. + * + * Required properties: + * - REPLICABLE: Two calls to `getVersion` on a file that has clearly not been modified must return the same version. + * - MONOTONOUS: The default version of a file is an increasing function of modification time. + * - CONSERVATIVE: If file f had its version last set to v, but the versioning implementation determines the file MIGHT + * have been modified and it chooses to return a version, it will return a value strictly larger than v. + * + * A common pattern to achieve monotonicity and conservativeness will be to invalidate the version of a data file + * if it is detected that the file was modified without updating the version (e.g. by a process which is unaware of versioning). + * + * @param <T> the type for the version objects. Must be comparable and serializable. + */ +public interface DataFileVersion<T extends Comparable<T> & Serializable> { + + /** + * Characteristics a {@link DataFileVersion} may have. + */ + enum Characteristic { + /** The default version for a data file is the modtime of the file. Versions can in general be compared against modtimes. */ + COMPATIBLE_WITH_MODTIME, + /** Version can be explicitly set. If false, `set*` methods will always return false */ + SETTABLE, + /** If a file has been modified and a set* method was not called, `getVersion` will throw an error. */ + STRICT + } + + String DATA_FILE_VERSION_KEY = "org.apache.gobblin.dataFileVersionStrategy"; + + /** + * Instantiate a {@link DataFileVersion} according to input configuration. + */ + static DataFileVersion instantiateDataFileVersion(FileSystem fs, Config config) throws IOException { + String versionStrategy = ConfigUtils.getString(config, DATA_FILE_VERSION_KEY, ModTimeDataFileVersion.Factory.class.getName()); + + ClassAliasResolver resolver = new ClassAliasResolver(DataFileVersionFactory.class); + + try { + Class<? extends DataFileVersionFactory> klazz = resolver.resolveClass(versionStrategy); + return klazz.newInstance().createDataFileVersionStrategy(fs, config); + } catch (ReflectiveOperationException roe) { + throw new IOException(roe); + } + } + + /** + * A Factory for {@link DataFileVersion}s. + */ + interface DataFileVersionFactory<T extends Comparable<T> & Serializable> { + /** + * Build a {@link DataFileVersion} with the input configuration. + */ + DataFileVersion<T> createDataFileVersionStrategy(FileSystem fs, Config config); + } + + /** + * Get the version of a path. + */ + T getVersion(Path path) throws IOException; + + /** + * Set the version of a path to a specific version (generally replicated from another path). + * + * @return whether the version was set successfully + */ + boolean setVersion(Path path, T version) throws IOException; + + /** + * Set the version of a path to a value automatically set by the versioning system. Note this call must respect the + * monotonicity requirement. + * + * @return whether the version was set successfully + */ + boolean setDefaultVersion(Path path) throws IOException; Review comment: In some way there are two operations you would want to do with versioning: set a version to the "current" or "default" value, and propagate the version from one file to another. For setting the version, the caller might not know which strategy the user chose, but the version might have a way to determine what the version of a file might be (e.g. current timestamp, or look up in a registry, etc.), so the caller would just call `setDefaultVersion`. For propagating a version, you can just get the version of one file, and apply it to the new file, without knowledge about what strategy the user chose. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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