Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/3522#discussion_r108477718
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/state/filesystem/AbstractFileStateBackend.java
---
@@ -0,0 +1,556 @@
+/*
+ * 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.state.filesystem;
+
+import org.apache.flink.annotation.PublicEvolving;
+import org.apache.flink.api.common.JobID;
+import org.apache.flink.configuration.ConfigConstants;
+import org.apache.flink.configuration.ConfigOption;
+import org.apache.flink.configuration.ConfigOptions;
+import org.apache.flink.configuration.Configuration;
+import org.apache.flink.configuration.IllegalConfigurationException;
+import org.apache.flink.core.fs.FileStatus;
+import org.apache.flink.core.fs.FileSystem;
+import org.apache.flink.core.fs.Path;
+import org.apache.flink.runtime.state.AbstractStateBackend;
+import org.apache.flink.runtime.state.CheckpointMetadataStreamFactory;
+import org.apache.flink.runtime.state.StateBackendGlobalHooks;
+import org.apache.flink.runtime.state.StreamStateHandle;
+import org.apache.flink.util.FileUtils;
+import org.apache.flink.util.FlinkException;
+import org.apache.flink.util.FlinkRuntimeException;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import javax.annotation.Nullable;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.net.URI;
+import java.net.URISyntaxException;
+
+import static org.apache.flink.util.Preconditions.checkArgument;
+import static org.apache.flink.util.Preconditions.checkNotNull;
+
+/**
+ * A base class for all state backends that store their metadata (and
data) in files.
+ * Examples that inherit from this are the {@link FsStateBackend}, the
+ * {@link org.apache.flink.runtime.state.memory.MemoryStateBackend
MemoryStateBackend}, or the
+ * {@code RocksDBStateBackend}.
+ *
+ * <p>This class takes the base checkpoint- and savepoint directory paths,
but also accepts null
+ * for both of then, in which case creating externalized checkpoint is not
possible, and it is not
+ * possible to create a savepoint with a default path. Null is accepted to
enable implementations
+ * that only optionally support default savepoints and externalized
checkpoints.
+ *
+ * <h1>Checkpoint Layout</h1>
+ *
+ * The state backend is configured with a base directory and persists the
checkpoint data of specific
+ * checkpoints in specific subdirectories. For example, if the base
directory was set to
+ * {@code hdfs://namenode:port/flink-checkpoints/}, the state backend will
create a subdirectory with
+ * the job's ID that will contain the actual checkpoints:
+ * ({@code
hdfs://namenode:port/flink-checkpoints/1b080b6e710aabbef8993ab18c6de98b})
+ *
+ * <p>Each checkpoint individually will store all its files in a
subdirectory that includes the
+ * checkpoint number, such as {@code
hdfs://namenode:port/flink-checkpoints/1b080b6e710aabbef8993ab18c6de98b/chk-17/}.
+ *
+ * <h1>Savepoint Layout</h1>
+ *
+ * A savepoint that is set to be stored in path {@code
hdfs://namenode:port/flink-savepoints/}, will create
+ * a subdirectory {@code savepoint-jobId(0, 6)-randomDigits} in which it
stores all savepoint data.
+ * The random digits are added as "entropy" to avoid directory collisions.
+ */
+@PublicEvolving
+public abstract class AbstractFileStateBackend extends
AbstractStateBackend implements StateBackendGlobalHooks {
+
+ private static final long serialVersionUID = 1L;
+
+ private static final Logger LOG =
LoggerFactory.getLogger(AbstractFileStateBackend.class);
+
+ //
------------------------------------------------------------------------
+ // Configuration
+ //
------------------------------------------------------------------------
+
+ /**
+ * The configuration parameter for the checkpoint path/directory.
+ */
+ public static final ConfigOption<String> CHECKPOINT_PATH = ConfigOptions
+ .key(ConfigConstants.CHECKPOINTS_DIRECTORY_KEY)
+ .noDefaultValue()
+ .withDeprecatedKeys("state.backend.fs.checkpointdir");
+
+ /**
+ * The configuration parameter for the savepoint path/directory.
+ */
+ public static final ConfigOption<String> SAVEPOINT_PATH = ConfigOptions
+ .key(ConfigConstants.SAVEPOINT_DIRECTORY_KEY)
+ .noDefaultValue()
+ .withDeprecatedKeys("state.backend.fs.savepointdir");
--- End diff --
Shall we move these `ConfigOptions` to a dedicated `StateOptions` class
which is put under `org.apache.flink.configuration`? I think most of the
options live there, currently.
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