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https://issues.apache.org/jira/browse/FLINK-2991?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15142700#comment-15142700
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ASF GitHub Bot commented on FLINK-2991:
---------------------------------------
Github user StephanEwen commented on a diff in the pull request:
https://github.com/apache/flink/pull/1605#discussion_r52599200
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/state/AbstractStateBackend.java
---
@@ -148,6 +150,18 @@ public void dispose() {
abstract protected <N, T> ReducingState<T>
createReducingState(TypeSerializer<N> namespaceSerializer,
ReducingStateDescriptor<T> stateDesc) throws Exception;
/**
+ * Creates and returns a new {@link FoldingState}.
+ *
+ * @param namespaceSerializer TypeSerializer for the state namespace.
+ * @param stateDesc The {@code StateDescriptor} that contains the name
of the state.
+ *
+ * @param <N> The type of the namespace.
+ * @param <T> Type of the values folded into the state
+ * @param <ACC> Type of the value in the state *
+ */
+ abstract protected <N, T, ACC> FoldingState<T, ACC>
createFoldingState(TypeSerializer<N> namespaceSerializer,
FoldingStateDescriptor<T, ACC> stateDesc) throws Exception;
--- End diff --
protected abstract
> Extend Window Operators to Allow Efficient Fold Operation
> ---------------------------------------------------------
>
> Key: FLINK-2991
> URL: https://issues.apache.org/jira/browse/FLINK-2991
> Project: Flink
> Issue Type: Improvement
> Components: Streaming
> Reporter: Aljoscha Krettek
> Assignee: Aljoscha Krettek
>
> Right now, a window fold is implemented as a WindowFunction that gets all the
> elements as input. No pre-aggregation is performed. The window operator
> should be extended to also allow the fold to also be pre-aggregated.
> This requires changing the signature of the {{WindowBuffer}} so that it can
> emit a type other than the input type.
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