mridulm commented on a change in pull request #28618: URL: https://github.com/apache/spark/pull/28618#discussion_r486084517
########## File path: core/src/main/java/org/apache/spark/shuffle/api/metadata/ShuffleOutputTracker.java ########## @@ -0,0 +1,56 @@ +/* + * 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.shuffle.api.metadata; + +/** + * :: Private :: + * + * A plugin that can monitor the storage of shuffle data from map tasks, and can provide + * metadata to shuffle readers to aid their reading of shuffle blocks in reduce tasks. + * <p> + * {@link MapOutputMetadata} instances provided from the plugin tree's implementation of + * {@link org.apache.spark.shuffle.api.ShuffleMapOutputWriter} are sent to + * <p> + * Implementations MUST be thread-safe. Spark will invoke methods in this module in parallel. Review comment: As an example, `registerShuffle` is invoked with write lock held, while `unregisterShuffle` is invoked without any lock. As a public api we are exposing, the locking semantics needs to be elaborated; so that users can evaluate what can be done safely/without contention, and what needs additional protection (for example, `updateMapOutput` can be performed without contention from `registerShuffle` or `registerMapOutput`) Additionally, it also informs users about how to design their implementations. For example, if an implementation makes rpc calls (or other blocking calls) from `registerMapOutput` , there could be nontrivial side effects in driver. (I just picked some api calls to illustrate, we need to elaborate for each). ---------------------------------------------------------------- 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] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
