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https://issues.apache.org/jira/browse/FLINK-5024?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15847080#comment-15847080
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ASF GitHub Bot commented on FLINK-5024:
---------------------------------------
Github user aljoscha commented on a diff in the pull request:
https://github.com/apache/flink/pull/3243#discussion_r98710331
--- Diff:
flink-core/src/main/java/org/apache/flink/api/common/state/StateDescriptor.java
---
@@ -20,34 +20,29 @@
import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.api.common.ExecutionConfig;
-import org.apache.flink.api.common.typeinfo.TypeInformation;
-import org.apache.flink.api.common.typeutils.TypeSerializer;
-import org.apache.flink.api.java.typeutils.TypeExtractor;
-import org.apache.flink.core.memory.DataInputViewStreamWrapper;
-import org.apache.flink.core.memory.DataOutputViewStreamWrapper;
import org.apache.flink.util.Preconditions;
-import java.io.ByteArrayInputStream;
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import java.io.ObjectInputStream;
-import java.io.ObjectOutputStream;
import java.io.Serializable;
import static java.util.Objects.requireNonNull;
/**
- * Base class for state descriptors. A {@code StateDescriptor} is used for
creating partitioned
- * {@link State} in stateful operations. This contains the name and can
create an actual state
- * object given a {@link StateBackend} using {@link #bind(StateBackend)}.
- *
+ * Base class for state descriptors. A {@code StateDescriptor} is used for
creating
+ * {@link State keyed state} in stateful operations. The descriptor
contains the name of the state,
--- End diff --
Just a quick note: `StateDescriptors` are also used for non-keyed state,
i.e. operator state.
> Add SimpleStateDescriptor to clarify the concepts
> -------------------------------------------------
>
> Key: FLINK-5024
> URL: https://issues.apache.org/jira/browse/FLINK-5024
> Project: Flink
> Issue Type: Improvement
> Components: State Backends, Checkpointing
> Reporter: Xiaogang Shi
> Assignee: Xiaogang Shi
>
> Currently, StateDescriptors accept two type arguments : the first one is the
> type of the created state and the second one is the type of the values in the
> states.
> The concepts however is a little confusing here because in ListStates, the
> arguments passed to the StateDescriptors are the types of the list elements
> instead of the lists. It also makes the implementation of MapStates difficult.
> I suggest not to put the type serializer in StateDescriptors, making
> StateDescriptors independent of the data structures of the values.
> A new type of StateDescriptor named SimpleStateDescriptor can be provided to
> abstract those states (namely ValueState, ReducingState and FoldingState)
> whose states are not composited.
> The states (e.g. ListStates and MapStates) can implement their own
> descriptors according to their data structures.
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