[
https://issues.apache.org/jira/browse/FLINK-39435?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
sherlock-lin updated FLINK-39435:
---------------------------------
Description:
In `KafkaSourceEnumerator.handlePartitionSplitChanges()`, there is a
long-standing `TODO` comment:
!image-2026-04-14-17-16-33-680.png!
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.
was:
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.
> [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,
> image-2026-04-14-17-16-33-680.png
>
>
> In `KafkaSourceEnumerator.handlePartitionSplitChanges()`, there is a
> long-standing `TODO` comment:
> !image-2026-04-14-17-16-33-680.png!
>
> 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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