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package org.apache.flink.streaming.api.operators; /** The builder class for {@link OperatorAttributes}. */ @PublicEvolving public class OperatorAttributesBuilder { @Nullable private Boolean ... outputStreamRecordValueStored = null; @Nullable private Boolean inputStreamRecordStored = null; public OperatorAttributesBuilder() { ... objectReuseCompliant = false; inputStreamRecordStored = true; } /** * Set to truefalse if it is guaranteed that the operator will not store and access reference to the * value of the StreamRecord StreamRecord#value that it has already emitted. */ public OperatorAttributesBuilder setObjectReuseCompliantsetOutputStreamRecordValueStored(boolean objectReuseCompliantoutputStreamRecordValueStored) {...} /** * Set to false if it is guaranteed that the operator will not store and access reference to the * input StreamRecord instance. */ public voidOperatorAttributesBuilder setInputStreamRecordStored(boolean inputStreamRecordStored) {...} /** * If any operator attribute is null, we will log it at DEBUG level and use the following * default values. * - outputStreamRecordValueStored defaults to true * - inputStreamRecordStored defaults to true */ public OperatorAttributes build() {...} } |
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package org.apache.flink.streaming.api.operators; /** * OperatorAttributes element provides Job Manager with information that can be * used to optimize job performance. */ @PublicEvolving public class OperatorAttributes { /** * Returns truefalse if it is guaranteed that the operator will not store and access reference to the * value of the StreamRecord StreamRecord#value that it has already emitted. */ public boolean isObjectReuseCompliantisOutputStreamRecordValueStored() {...} /** * Return false if it is guaranteed that the operator will not store and access reference to the * input StreamRecord instance. */ public boolean isInputStreamRecordStored() {...} } |
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@PublicEvolving public interface StreamOperator<OUT> extends CheckpointListener, KeyContext, Serializable { ... default OperatorAttributes getOperatorAttributes() { return new OperatorAttributesBuilder().build(); } } @PublicEvolving public interface StreamOperatorFactory<OUT> extends Serializable { ... default OperatorAttributes getOperatorAttributes() { return new OperatorAttributesBuilder().build(); } } |
3) Add the isObjectReuseCompliant
isOutputValueStored
method that returns false
by default to the Function
interface. And the RichFunction
overwrite the isOutputValueStored
method to return true
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@Public public interface Function extends java.io.Serializable { /** * Returns truefalse if it is guaranteed that the function will not store and access * reference to the output value. */ default boolean isObjectReuseCompliantisOutputValueStored() { return true; } } @Public public interface RichFunction extends Function { /** * RichFunction is able to put the values to the state backend so the method returns true by * default. For RichFunction that doesn't store output value to the state backend, it can return * false. */ @Override default boolean isOutputValueStored() { return true; } } |
4) Update the description of pipeline.object-reuse
to mention that when it is false, Flink will decide whether to use object reuse based on the operator attributes.
Here is the updated description:
When it is true, objects that Flink internally uses for deserialization and passing data to user-code functions will be reused. When it is false, Flink will decide whether to use object reuse based on the operator attributes. Keep in mind that this can lead to bugs when the user-code function of an operation is not aware of this behavior.
Proposed Changes
1) Update OperatorChain
to take advantage of the isObjectReuseCompliant
isOutputStreamRecordValueStored
and isInputStreamRecordStored
attribute.
Currently, the OperatorChain
only considers the global execution configuration pipeline.object-reuse
to determine whether to enable object-reuse for data transfer between chained operators.
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If
pipeline.object-reuse
is set to true, records emitted by this operator will be re-used.Otherwise, if i
sObjectReuseCompliantisOutputStreamRecordValueStored()
returns truefalseIf the downstream operator
isInputStreamRecordStored()
return false, records emitted by this operator will be re-used.- Otherwise,
StreamRecord
will be shallow-copied before being given to the next operator in the chain.
Otherwise, records emitted by this operator will be deep-copied before being given to the next operator in the chain.
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2) Update operators/functions defined in Flink codebase to override the i sObjectReuseCompliantisOutputStreamRecordValueStored()
as appropriate.
We will enumerate all operators/functions defined in Flink, identify those operators/functions which that do not store or access reference to the value of the output StreamRecord, and override their i sObjectReuseCompliantisOutputStreamRecordValueStored()
method to return truefalse. Those operators which that do not store or or access reference to the input StreamRecord
should override the isInputStreamRecordStored()
method to return false.
After implementing the proposed change, the operator/function developer will have the flexibility to avoid unnecessary deep-copy overhead by appropriately overriding the i sObjectReuseCompliantisOutputStreamRecordValueStored()
method. This empowers Flink to achieve optimal performance with the default configuration.
POC and Analysis
We implement a POC and run the flink-benchmarks against the POC with global object-reuse disabled. We verify that, with the change proposed in the FLIP, many of the operators in the benchmark can enable object-reuse without code change. Only the custom operator and the AbstractUdfStreamOperator
that contains a RichFunction
cannot enable object-reuse to its output. In order to enable object-reuse of those operator/function, couple lines of code are needed to set the operator attributes accordingly. After that, all the operator in flink-benchmarks can enable object-reuse with the global object-reuse disable.
Compatibility, Deprecation, and Migration Plan
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Migration plan: users are recommended to update their existing operator/function implementation to override the i sObjectReuseCompliantisOutputStreamRecordValueStored()
API if their operator/function does not store and access reference to the records StreamRecord#value
that it has already emitted. And override the isInputStreamRecordStored()
API if their operator does not store and access the input StreamRecord
instance. We plan to write blogs to promote the new API.
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