Github user uce commented on a diff in the pull request:
https://github.com/apache/flink/pull/1153#discussion_r41149990
--- 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 --
I think that won't work. It can happen that two concurrent checkpoints
return the same checkpoint ID, because creating a new node and getting the
cversion after that operation is not atomic. We can do it with
`persistent_sequential` nodes, but this will imo add complexity than reduce it.
These are corner cases of course, but the counter makes the semantics clearer
imo.
We could merge the counter into the `CompletedCheckpointsStore`?
---
If your project is set up for it, you can reply to this email and have your
reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
contact infrastructure at infrastruct...@apache.org or file a JIRA ticket
with INFRA.
---
