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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-5715) Asynchronous snapshotting for HeapKeyedStateBackend
Date Thu, 16 Mar 2017 10:39:41 GMT

    [ https://issues.apache.org/jira/browse/FLINK-5715?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15927806#comment-15927806
] 

ASF GitHub Bot commented on FLINK-5715:
---------------------------------------

Github user StefanRRichter commented on a diff in the pull request:

    https://github.com/apache/flink/pull/3466#discussion_r106385143
  
    --- Diff: flink-runtime/src/main/java/org/apache/flink/runtime/state/filesystem/FsStateBackend.java
---
    @@ -97,6 +100,27 @@ public FsStateBackend(String checkpointDataUri) throws IOException
{
     	 *
     	 * @param checkpointDataUri The URI describing the filesystem (scheme and optionally
authority),
     	 *                          and the path to the checkpoint data directory.
    +	 * @param asynchronousSnapshots Switch to enable asynchronous snapshots.
    +	 *
    +	 * @throws IOException Thrown, if no file system can be found for the scheme in the
URI.
    +	 */
    +	public FsStateBackend(String checkpointDataUri, boolean asynchronousSnapshots) throws
IOException {
    --- End diff --
    
    For now, I suggest to keep it as is and as soon as your PR goes in, we have a followup,
that introduced a single entry point to a builder for all backend related configuration options
that helps the user to see and navigate all options in a more centralized way, e.g. `KeyedBackends.heap().async(true).create()`.



> Asynchronous snapshotting for HeapKeyedStateBackend
> ---------------------------------------------------
>
>                 Key: FLINK-5715
>                 URL: https://issues.apache.org/jira/browse/FLINK-5715
>             Project: Flink
>          Issue Type: New Feature
>          Components: State Backends, Checkpointing
>    Affects Versions: 1.3.0
>            Reporter: Stefan Richter
>            Assignee: Stefan Richter
>
> Blocking snapshots render the HeapKeyedStateBackend practically unusable for many user
in productions. Their jobs can not tolerate stopped processing for the time it takes to write
gigabytes of data from memory to disk. Asynchronous snapshots would be a solution to this
problem. The challenge for the implementation is coming up with a copy-on-write scheme for
the in-memory hash maps that build the foundation of this backend. After taking a closer look,
this problem is twofold. First, providing CoW semantics for the hashmap itself, as a mutible
structure, thereby avoiding costly locking or blocking where possible. Second, CoW for the
mutable value objects, e.g. through cloning via serializers.  



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