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Posted to reviews@helix.apache.org by "desaikomal (via GitHub)" <gi...@apache.org> on 2023/05/16 17:55:28 UTC
[GitHub] [helix] desaikomal commented on a diff in pull request #2488: add leader election API and dummy class
desaikomal commented on code in PR #2488:
URL: https://github.com/apache/helix/pull/2488#discussion_r1195506806
##########
meta-client/src/main/java/org/apache/helix/metaclient/recipes/leaderelection/LeaderElectionClient.java:
##########
@@ -0,0 +1,125 @@
+package org.apache.helix.metaclient.recipes.leaderelection;
+
+/*
+ * 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.List;
+
+import org.apache.helix.metaclient.api.MetaClientInterface;
+import org.apache.helix.metaclient.factories.MetaClientConfig;
+
+
+/**
+ * LeaderElectionClient does distributed leader election using CRUD and change notification APIs
+ * provided by underlying metadata client. Leader election config can provide many
+ * configs like base path for all participating nodes, sync/async mode, TTL etc.
+ *
+ * Participants join a leader election group by calling the following API.
Review Comment:
nit: all sentences can end with '.' at the end. just a nit.
##########
meta-client/src/main/java/org/apache/helix/metaclient/recipes/leaderelection/LeaderElectionClient.java:
##########
@@ -0,0 +1,125 @@
+package org.apache.helix.metaclient.recipes.leaderelection;
+
+/*
+ * 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.List;
+
+import org.apache.helix.metaclient.api.MetaClientInterface;
+import org.apache.helix.metaclient.factories.MetaClientConfig;
+
+
+/**
+ * LeaderElectionClient does distributed leader election using CRUD and change notification APIs
+ * provided by underlying metadata client. Leader election config can provide many
+ * configs like base path for all participating nodes, sync/async mode, TTL etc.
+ *
+ * Participants join a leader election group by calling the following API.
+ * The Leader Election client maintains and elect an active leader from participant pool
+ * All participants wanted to be elected as leader joins a pool
+ * LeaderElection client maintains an active leader, by monitoring liveness of current leader and
+ * re-elect if needed and user no need to call elect or re-elect explicitly.
+ * This LeaderElection client will notify registered listeners for any leadership change.
+ */
+public class LeaderElectionClient {
+
+ /**
+ * Construct a LeaderElectionClient using a user passed in leaderElectionConfig. It creates a MetaClient
+ * instance underneath.
+ * When MetaClient is auto closed be cause of being disconnected and auto retry connection timed out, A new
+ * MetaClient instance will be created and keeps retry connection.
+ */
+ public LeaderElectionClient(MetaClientConfig metaClientConfig) {
+
+ }
+
+ /**
+ * Construct a LeaderElectionClient using a user passed in MetaClient object
+ * When MetaClient is auto closed be cause of being disconnected and auto retry connection timed out, user
+ * will need to create a new MetaClient and a new LeaderElectionClient instance.
+ */
+ public LeaderElectionClient(MetaClientInterface MetaClient) {
+
+ }
+
+ /**
+ * Returns true if current participant is able to acquire leadership.
+ */
+ public boolean isLeader(String leaderPath, String participant) {
+ return false;
+ }
+
+ /**
+ * Participants join a leader election group by calling the following API.
+ * The Leader Election client maintains and elect an active leader from participant pool
+ */
+ public boolean joinLeaderElectionParticipantPool(String leaderPath, String participant,
+ Object userInfo) {
+ return false;
+ }
+
+ /**
+ * Any participant may exit the exitLeaderElectionParticipantPool by calling the API.
+ * If the participant is not the current leader, it leaves the pool and won't be elected as next leader.
+ * If the participant is the current leader, it leaves the pool and a new leader will be elected if there are other participants in the pool.
+ * Throws exception if the participant is not in the pool.
+ */
+ public boolean exitLeaderElectionParticipantPool(String leaderPath, String participant) {
+ return false;
+ }
+
+ /**
+ * Releases leadership for participant.
+ * Throws exception if the leadership is not owned by this participant.
+ */
+ public void relinquishLeader(String leaderPath, String participant) {
+ }
+
+ /**
+ * Get current leader nodes.
+ * Returns null if no Leader at a given point.
+ */
+ public String getLeader(String leaderPath) {
+ return null;
+ }
+
+ /**
+ * Return a list of hosts in participant pool
+ */
+ public List<String> getFollowers(String leaderPath) {
Review Comment:
getParticipants sounds appropriate. this is not master/follower correct?
##########
meta-client/src/main/java/org/apache/helix/metaclient/recipes/leaderelection/LeaderElectionClient.java:
##########
@@ -0,0 +1,125 @@
+package org.apache.helix.metaclient.recipes.leaderelection;
+
+/*
+ * 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.List;
+
+import org.apache.helix.metaclient.api.MetaClientInterface;
+import org.apache.helix.metaclient.factories.MetaClientConfig;
+
+
+/**
+ * LeaderElectionClient does distributed leader election using CRUD and change notification APIs
+ * provided by underlying metadata client. Leader election config can provide many
+ * configs like base path for all participating nodes, sync/async mode, TTL etc.
+ *
+ * Participants join a leader election group by calling the following API.
+ * The Leader Election client maintains and elect an active leader from participant pool
+ * All participants wanted to be elected as leader joins a pool
+ * LeaderElection client maintains an active leader, by monitoring liveness of current leader and
+ * re-elect if needed and user no need to call elect or re-elect explicitly.
+ * This LeaderElection client will notify registered listeners for any leadership change.
+ */
+public class LeaderElectionClient {
+
+ /**
+ * Construct a LeaderElectionClient using a user passed in leaderElectionConfig. It creates a MetaClient
+ * instance underneath.
+ * When MetaClient is auto closed be cause of being disconnected and auto retry connection timed out, A new
+ * MetaClient instance will be created and keeps retry connection.
+ */
+ public LeaderElectionClient(MetaClientConfig metaClientConfig) {
+
+ }
+
+ /**
+ * Construct a LeaderElectionClient using a user passed in MetaClient object
+ * When MetaClient is auto closed be cause of being disconnected and auto retry connection timed out, user
+ * will need to create a new MetaClient and a new LeaderElectionClient instance.
+ */
+ public LeaderElectionClient(MetaClientInterface MetaClient) {
+
+ }
+
+ /**
+ * Returns true if current participant is able to acquire leadership.
+ */
+ public boolean isLeader(String leaderPath, String participant) {
+ return false;
+ }
+
+ /**
+ * Participants join a leader election group by calling the following API.
+ * The Leader Election client maintains and elect an active leader from participant pool
+ */
+ public boolean joinLeaderElectionParticipantPool(String leaderPath, String participant,
+ Object userInfo) {
+ return false;
+ }
+
+ /**
+ * Any participant may exit the exitLeaderElectionParticipantPool by calling the API.
+ * If the participant is not the current leader, it leaves the pool and won't be elected as next leader.
+ * If the participant is the current leader, it leaves the pool and a new leader will be elected if there are other participants in the pool.
+ * Throws exception if the participant is not in the pool.
+ */
+ public boolean exitLeaderElectionParticipantPool(String leaderPath, String participant) {
+ return false;
+ }
+
+ /**
+ * Releases leadership for participant.
+ * Throws exception if the leadership is not owned by this participant.
+ */
+ public void relinquishLeader(String leaderPath, String participant) {
+ }
+
+ /**
+ * Get current leader nodes.
+ * Returns null if no Leader at a given point.
+ */
+ public String getLeader(String leaderPath) {
+ return null;
+ }
+
+ /**
+ * Return a list of hosts in participant pool
+ */
+ public List<String> getFollowers(String leaderPath) {
+ return null;
+ }
+
+ /**
+ * APIs to register/unregister listener to leader path. All the participants can listen to any
+ * leaderPath, Including leader going down or a new leader comes up.
+ * Whenever current leader for that leaderPath goes down (considering it's ephemeral entity which
+ * get's auto-deleted after TTL or session timeout) or a new leader comes up, it notifies all
+ * participants who have been listening on entryChange event.
+ */
+ public boolean subscribeLeadershipChanges(String leaderPath,
Review Comment:
what is the contract - when leaderPath doesn't exist? will we create and wait for others to participate?
##########
meta-client/src/main/java/org/apache/helix/metaclient/recipes/leaderelection/LeaderInfo.java:
##########
@@ -0,0 +1,42 @@
+package org.apache.helix.metaclient.recipes.leaderelection;
+
+/*
+ * 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 org.apache.helix.metaclient.datamodel.DataRecord;
+
+
+public class LeaderInfo {
+
+ private String _leaderElectionGroupName;
+ private final DataRecord _record;
+
+
+ public LeaderInfo( String leaderElectionGroupName) {
+ _leaderElectionGroupName = leaderElectionGroupName;
+ _record = new DataRecord(_leaderElectionGroupName);
+ }
+
+ public enum LeaderAttribute {
+ LEADER_NAME,
+ PARTICIPANTS_LIST
Review Comment:
Are these meta data which will be persisted?
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