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_r263622989
########## 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 Review comment: It means to fallback to default version if anything external has modified the file I guess? I can rephrase this. STRICT does mean that if a modification was made, `getVersion` will return an error to indicate that. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected] With regards, Apache Git Services
