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https://issues.apache.org/jira/browse/FLINK-5715?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15899687#comment-15899687
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ASF GitHub Bot commented on FLINK-5715:
---------------------------------------
Github user aljoscha commented on a diff in the pull request:
https://github.com/apache/flink/pull/3466#discussion_r104671557
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/state/ArrayListSerializer.java
---
@@ -53,11 +53,7 @@ public boolean isImmutableType() {
@Override
public ArrayList<T> copy(ArrayList<T> from) {
- ArrayList<T> newList = new ArrayList<>(from.size());
- for (int i = 0; i < from.size(); i++) {
- newList.add(elementSerializer.copy(from.get(i)));
- }
- return newList;
+ return new ArrayList<>(from);
--- End diff --
The old code was "slow" on purpose. 😉 (We need the deep copy here)
> 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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