Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/1153#discussion_r41158214
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/checkpoint/ZooKeeperCheckpointIDCounter.java
---
@@ -0,0 +1,130 @@
+/*
+ * 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.flink.runtime.checkpoint;
+
+import org.apache.curator.framework.CuratorFramework;
+import org.apache.curator.framework.recipes.shared.SharedCount;
+import org.apache.curator.framework.recipes.shared.VersionedValue;
+import org.apache.curator.framework.state.ConnectionState;
+import org.apache.curator.framework.state.ConnectionStateListener;
+import org.apache.flink.runtime.jobmanager.RecoveryMode;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * {@link CheckpointIDCounter} instances for JobManagers running in {@link
RecoveryMode#ZOOKEEPER}.
+ *
+ * <p>Each counter creates a ZNode:
+ * <pre>
+ * +----O /flink/checkpoint-counter/<job-id> 1 [persistent]
+ * .
+ * .
+ * .
+ * +----O /flink/checkpoint-counter/<job-id> N [persistent]
+ * </pre>
+ *
+ * <p>The checkpoints IDs are required to be ascending (per job). In order
to guarantee this in case
+ * of job manager failures we use ZooKeeper to have a shared counter
across job manager instances.
+ */
+public class ZooKeeperCheckpointIDCounter implements CheckpointIDCounter {
--- End diff --
As talked offline: It's seems to be ok that concurrently running jobs have
overlapping checkpoint IDs. Thus, using ZooKeeper's provided sequential ID to
distinguish checkpoint nodes unambiguously and using a checkpoint ID counter on
a JobManager basis should be ok.
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