Github user StephanEwen commented on a diff in the pull request:
https://github.com/apache/flink/pull/4907#discussion_r147090207
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/state/filesystem/AbstractFileStateBackend.java
---
@@ -0,0 +1,206 @@
+/*
+ * 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.configuration.CheckpointingOptions;
+import org.apache.flink.configuration.ConfigOption;
+import org.apache.flink.configuration.Configuration;
+import org.apache.flink.configuration.IllegalConfigurationException;
+import org.apache.flink.core.fs.Path;
+import org.apache.flink.runtime.state.AbstractStateBackend;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import javax.annotation.Nullable;
+import java.net.URI;
+
+/**
+ * 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
--- End diff --
The main difference between `FsStatebackend` and `MemoryStateBackend` is
the following (already now as well, BTW):
- `FsStateBackend` writes directly individual files for individual state
chunks and always writes out metadata to a file.
- `MemoryStateBackend` aggregates all state (data and metadata) in a
single file. It only writes that file of a checkpoint directory is configured,
or if HA is activated, otherwise it just keeps it in the JobManager's memory.
Thats so that one can start playing around without any checkpoint config.
---
