Github user ajs6f commented on a diff in the pull request: https://github.com/apache/jena/pull/369#discussion_r172251788 --- Diff: jena-arq/src/main/java/org/apache/jena/sparql/core/TxnDataset2Graph.java --- @@ -0,0 +1,240 @@ +/* + * 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.jena.sparql.core; + +import java.util.*; +import java.util.function.Consumer; + +import org.apache.jena.graph.Graph; +import org.apache.jena.graph.TransactionHandler; +import org.apache.jena.query.ReadWrite; +import org.apache.jena.query.TxnType; +import org.apache.jena.reasoner.InfGraph; +import org.apache.jena.shared.LockMRSW; +import org.apache.jena.sparql.JenaTransactionException; + +/** + * A {@link Transactional} that passes the transaction operations down to transactions on + * independent graphs. + * <p> + * There are limitations: + * <ul> + * <li>we can't atomically do all the commits together in the crash situation. + * <li>This {@code Transactional} maintains a MRSW policy because that is all that is + * required of graphs in general. + * </ul> + * It does cover the important case of one graph ({@link DatasetGraphOne}) where the one + * graph is an InfGraph and should work when the graphs in the dataset is not changing or + * when a new memory graph is added mid-transaction. + * <p> + * This is not "nested transactions" - theer is no overall "commit" or "abort". If + * failure/restart occurs, some graphs may have commited and others not. It is the best + * that can be done given for an arbitrary collection of graphs, backed by different + * storage and having different capabilities. + * <p> + * Best practice is to change the graph membership outside of any transaction, + * ideally at setup time of the object using this class. (Caution: SPARQL Update + * can create graphs. + * @See {@link DatasetGraphMapLink} + * @See {@link DatasetGraphOne} + */ +public class TxnDataset2Graph extends TransactionalLock { + /** + * Control whether to pass down transactions from the dataset to the graph in the + * dataset. This should be set to "true"; setting it "false" causes the onld, --- End diff -- `onld` => `old`
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