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From aljoscha <...@git.apache.org>
Subject [GitHub] flink pull request #4397: [FLINK-7265] [FLINK-7266] Introduce FileSystemKind...
Date Fri, 28 Jul 2017 07:18:37 GMT
Github user aljoscha commented on a diff in the pull request:

    https://github.com/apache/flink/pull/4397#discussion_r130027082
  
    --- Diff: flink-core/src/main/java/org/apache/flink/core/fs/ConsistencyLevel.java ---
    @@ -0,0 +1,119 @@
    +/*
    + * 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.core.fs;
    +
    +import org.apache.flink.annotation.PublicEvolving;
    +
    +/**
    + * An enumeration describing the level of consistency offered by a {@link FileSystem}.
    + * 
    + * <p>The consistency levels described here make statements about the visibility
    + * of file existence and file contents in the presence of <i>new file creation</i>,
    + * <i>file deletion</i>, <i>file renaming</i>, and <i>directory
listing</i>.
    + * 
    + * <p>An operation is defined as consistent if the following holds: After the function
    + * call triggering the operation returns, its result is immediately reflected in
    + * in the view presented to any other party calling a file system function.
    + * 
    + * <p>Please note that these levels do not make any statements about the effects
or visibility of
    + * file content modification or file appends. In fact, content modification or appending
are
    + * not supported in various file systems.
    + * 
    + * <p>Some of these consistency levels indicate that the storage system does not
actually
    + * qualify to be called a FileSystem, but rather a blob-/object store.
    + */
    +@PublicEvolving
    +public enum ConsistencyLevel {
    --- End diff --
    
    Have you thought about making the individual properties fields of the enum, i.e. have
fields for `newFileCreation`, `fileDeletion`, `fileRenaming`, `directoryListing`. Then `READ_AFTER_CREATE`
would become, for example, `READ_AFTER_CREATE(CONSISTENT, NOT_CONSISTENT, NOT_CONSISTENT,
NOT_CONSISTENT)`, and so on. I'm not sure whether the fields would be booleans or another
enum themselves. It seems there is at least `CONSISTENT`, `NOT_CONSISTENT`, and `ATOMIC`.
    
    That's just something to consider when merging this on master. I think we can merge as
is to fix the problem people are having with checkpointing to S3.


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