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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-7265) FileSystems should describe their kind and consistency level
Date Fri, 28 Jul 2017 07:19:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-7265?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16104573#comment-16104573
] 

ASF GitHub Bot commented on FLINK-7265:
---------------------------------------

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.


> FileSystems should describe their kind and consistency level
> ------------------------------------------------------------
>
>                 Key: FLINK-7265
>                 URL: https://issues.apache.org/jira/browse/FLINK-7265
>             Project: Flink
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 1.3.1
>            Reporter: Stephan Ewen
>            Assignee: Stephan Ewen
>             Fix For: 1.4.0, 1.3.2
>
>
> Currently, all {{FileSystem}} types look the same to Flink.
> However, certain operations should only be executed on certain kinds of file systems.
> For example, it makes no sense to attempt to delete an empty parent directory on S3,
because there are no such thinks as directories, only hierarchical naming in the keys (file
names).



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