narendly commented on a change in pull request #727: Add MetadataStoreRoutingDataWriter and its ZK implementation with DistributedLock URL: https://github.com/apache/helix/pull/727#discussion_r375675502
########## File path: helix-rest/src/main/java/org/apache/helix/rest/metadatastore/accessor/ZkRoutingDataWriter.java ########## @@ -0,0 +1,265 @@ +package org.apache.helix.rest.metadatastore.accessor; + +/* + * 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. + */ + +import java.util.Collections; +import java.util.List; +import java.util.Map; + +import org.I0Itec.zkclient.exception.ZkNodeExistsException; +import org.apache.helix.ZNRecord; +import org.apache.helix.manager.zk.ZNRecordSerializer; +import org.apache.helix.manager.zk.ZkBaseDataAccessor; +import org.apache.helix.manager.zk.client.DedicatedZkClientFactory; +import org.apache.helix.manager.zk.client.HelixZkClient; +import org.apache.helix.rest.metadatastore.concurrency.DistributedLock; +import org.apache.helix.rest.metadatastore.concurrency.ZkDistributedLock; +import org.apache.helix.rest.metadatastore.constant.MetadataStoreRoutingConstants; +import org.apache.helix.rest.metadatastore.exceptions.ZkLockException; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + + +public class ZkRoutingDataWriter implements MetadataStoreRoutingDataWriter { + private static final Logger LOG = LoggerFactory.getLogger(ZkBaseDataAccessor.class); + + private final String _namespace; + private final String _zkAddress; + private final HelixZkClient _zkClient; + private final DistributedLock _routingDataLock; Review comment: @dasahcc I agree that making Helix API service (Helix REST) an Helix application is a clever solution, but I have some concerns about that approach - wouldn't we be creating a circular dependency? As in, Helix cluster has problems, which causes problems with REST's single writer invariant, and you need to use REST endpoints to fix Helix cluster but REST has problems... and so on. Also, there was an agreement on this approach with users of Helix because we have an assumption that write operations are rare. Ideally, all operations provided by the writer would be ACL-ed and will only be done by admin. In that sense, I believe this is an appropriate approach since it is simple, self-contained without any other dependency (say Helix controller), and it follows a distributed lock recipe that ZooKeeper is very well-known and tested for. ---------------------------------------------------------------- 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 --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
