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https://issues.apache.org/jira/browse/FLINK-39435?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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sherlock-lin updated FLINK-39435:
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Attachment: image-2026-04-14-17-15-57-350.png
> [flink-connector-kafka] Switching Kafka topics via Savepoint restore causes
> dual-topic consumption AND new topic consumed from earliest instead of
> configured offset
> --------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: FLINK-39435
> URL: https://issues.apache.org/jira/browse/FLINK-39435
> Project: Flink
> Issue Type: Bug
> Environment: - Flink version: 1.17.0
> Reporter: sherlock-lin
> Priority: Major
> Labels: bug, flink-connector-kafka
> Attachments: image-2026-04-14-17-15-57-350.png
>
>
> In `KafkaSourceEnumerator.handlePartitionSplitChanges()`, there is a
> long-standing `TODO` comment:
> {quote}```
> // TODO: Handle removed partitions.
> addPartitionSplitChangeToPendingAssignments(partitionSplitChange.newPartitionSplits);
> assignPendingPartitionSplits(context.registeredReaders().keySet());
> ```
>
> {quote}
> Two separate bugs are triggered simultaneously:
> *{*}Bug 1 — Dual-topic consumption (old topic is never stopped){*}*
> The job consumes from *{*}both `topic-A` and `topic-B` simultaneously{*}*:
> - `topic-A` splits come from the *{*}Reader State{*}* restored from
> Savepoint (`SourceOperator.open()` →
> `sourceReader.addSplits(restoredSplits)`).
> - `topic-B` splits come from the *{*}Enumerator{*}* discovering new
> partitions (`initializePartitionSplits()` → `assignSplits()`).
> - In `KafkaPartitionSplitReader.handleSplitsChanges()`, line:
> ```java
> newPartitionAssignments.addAll(consumer.assignment()); // merges, does NOT
> replace
> consumer.assign(newPartitionAssignments);
> ```
> The old topic's partitions remain in the consumer assignment permanently. The
> Enumerator detects the removed partitions in `getPartitionChange()` but does
> nothing with them (`// TODO: Handle removed partitions.`).
> *{*}Bug 2 — New topic consumed from earliest instead of configured
> `latest()`{*}*
> Even though the job is configured with
> `.setStartingOffsets(OffsetsInitializer.latest())`, the new topic (`topic-B`)
> is consumed from the *{*}earliest{*}* available offset.
> Log evidence:
> ```
> INFO KafkaSourceEnumerator - Assigning splits to readers
> {57=[[Partition: topic-B-0, StartingOffset: -2, StoppingOffset:
> -9223372036854775808], ...]}
> ```
> Sentinel `-2` = `EARLIEST_OFFSET`, not `-1` (`LATEST_OFFSET`) as configured.
> Root cause: `setStartingOffsets()` only takes effect for *{*}truly new
> partitions{*}* discovered by the Enumerator. During Savepoint restore, the
> Reader State injects old splits directly into the Reader via
> `SourceOperator.open() → sourceReader.addSplits(restoredSplits)`, bypassing
> `setStartingOffsets()` entirely. The default `startingOffsetsInitializer` in
> `KafkaSourceBuilder` (line 106) is `OffsetsInitializer.earliest()`, and for
> partitions not found in Reader State this default is used instead of the
> user-configured value.
> *{*}Expected behavior{*}*
> When `getPartitionChange()` detects `removedPartitions`, the Enumerator
> should send a signal to the affected Readers to *{*}unassign{*}* those
> partitions from their `KafkaConsumer`, so the job only consumes from the
> newly subscribed topic.
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