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https://issues.apache.org/jira/browse/FLINK-34258?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17811775#comment-17811775
]
Jane Chan commented on FLINK-34258:
-----------------------------------
The generated AggHandler can be found in the attachment.
To highlight the problem, I quoted the `getAccumulators` and `emitValue`
methods here.
Even if `agg0_acc_external` got updated within `emitValue`, without
`getAccumulators` converting `agg0_acc_external` to `agg0_acc_internal`, the
`GroupTableAggFunction` would not get the updated accumulator.
{code:java}
@Override
public org.apache.flink.table.data.RowData getAccumulators() throws
Exception {
acc$3 = new org.apache.flink.table.data.GenericRowData(1);
agg0_acc_internal = (org.apache.flink.table.data.RowData)
converter$0.toInternalOrNull(
(org.apache.flink.table.planner.runtime.utils.JavaUserDefinedTableAggFunctions.Top2Accumulator)
agg0_acc_external);
if (false) {
acc$3.setField(0, null);
} else {
acc$3.setField(0, agg0_acc_internal);
}
return acc$3;
}
@Override
public void emitValue(
org.apache.flink.util.Collector<org.apache.flink.table.data.RowData> out,
org.apache.flink.table.data.RowData key, boolean isRetract)
throws Exception {
convertCollector.reset(key, isRetract, out);
function_org$apache$flink$table$planner$runtime$utils$JavaUserDefinedTableAggFunctions$IncrementalTop2
.emitUpdateWithRetract(agg0_acc_external, convertCollector);
}
{code}
> Incorrect example of accumulator usage within emitUpdateWithRetract for
> TableAggregateFunction
> ----------------------------------------------------------------------------------------------
>
> Key: FLINK-34258
> URL: https://issues.apache.org/jira/browse/FLINK-34258
> Project: Flink
> Issue Type: Bug
> Components: Documentation, Table SQL / API
> Affects Versions: 1.19.0, 1.18.1
> Reporter: Jane Chan
> Priority: Minor
> Attachments: GroupTableAggHandler$10.java
>
>
> The
> [documentation|https://nightlies.apache.org/flink/flink-docs-master/docs/dev/table/functions/udfs/#retraction-example]
> provides an example of using `emitUpdateWithRetract`. However, the example
> is misleading as it incorrectly suggests that the accumulator can be updated
> within the `emitUpdateWithRetract method`. In reality, the order of
> invocation is to first call `getAccumulator` and then
> `emitUpdateWithRetract`, which means that updating the accumulator within
> `emitUpdateWithRetract` will not take effect. Please see
> [GroupTableAggFunction#L141|https://github.com/apache/flink/blob/20450485b20cb213b96318b0c3275e42c0300e15/flink-table/flink-table-runtime/src/main/java/org/apache/flink/table/runtime/operators/aggregate/GroupTableAggFunction.java#L141]
> ~
> [GroupTableAggFunction#L146|https://github.com/apache/flink/blob/20450485b20cb213b96318b0c3275e42c0300e15/flink-table/flink-table-runtime/src/main/java/org/apache/flink/table/runtime/operators/aggregate/GroupTableAggFunction.java#L146]
> for more details.
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