[FLINK-39321][pipeline-connector-paimon]Fixes a bug where Flink CDC fails to write to Paimon dynamic bucket tables when dynamic-bucket.initial-buckets=1 and Flink parallelism > 1.

[zhaoruifeng01]

This closes FLINK-39321

What is the purpose of the change

This pull request fixes a bug where Flink CDC fails to write to Paimon dynamic bucket tables when dynamic-bucket.initial-buckets=1 and Flink parallelism > 1. The issue is caused by a parameter mismatch between the routing calculation in PaimonHashFunction (via RowAssignerChannelComputer ) and the assigner validation in BucketAssignOperator (via HashBucketAssigner ). When numAssigners=1 , all data should route to assigner 0, but BucketAssignOperator creates HashBucketAssigner instances with different assignId values for each subtask, causing validation failures.

Brief change log

• Modified BucketAssignOperator.java to set assignId=0 and numChannels=1 when minAssigners=1
• This ensures that all subtasks have consistent assigner parameters when numAssigners=1
• Aligns with the design principle that all data should route to assigner 0 when numAssigners=1

Verifying this change

Manually verified the change by:

1. Creating a Paimon table with dynamic bucket mode ( bucket=-1 ) and dynamic-bucket.initial-buckets=1
2. Configuring Flink CDC pipeline with parallelism=4
3. Starting the Flink CDC job to write data to the Paimon table
4. Verifying that data is written successfully without the IllegalArgumentException
5. Verifying that all data routes to subtask 0 when numAssigners=1

Does this pull request potentially affect one of the following parts

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @public(Evolving) : no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicableThis closes FLINK-39321

What is the purpose of the change

This pull request fixes a bug where Flink CDC fails to write to Paimon dynamic bucket tables when dynamic-bucket.initial-buckets=1 and Flink parallelism > 1. The issue is caused by a parameter mismatch between the routing calculation in PaimonHashFunction (via RowAssignerChannelComputer ) and the assigner validation in BucketAssignOperator (via HashBucketAssigner ). When numAssigners=1 , all data should route to assigner 0, but BucketAssignOperator creates HashBucketAssigner instances with different assignId values for each subtask, causing validation failures.

Brief change log

• Modified BucketAssignOperator.java to set assignId=0 and numChannels=1 when minAssigners=1
• This ensures that all subtasks have consistent assigner parameters when numAssigners=1
• Aligns with the design principle that all data should route to assigner 0 when numAssigners=1

Verifying this change

Manually verified the change by:

1. Creating a Paimon table with dynamic bucket mode ( bucket=-1 ) and dynamic-bucket.initial-buckets=1
2. Configuring Flink CDC pipeline with parallelism=4
3. Starting the Flink CDC job to write data to the Paimon table
4. Verifying that data is written successfully without the IllegalArgumentException
5. Verifying that all data routes to subtask 0 when numAssigners=1

Does this pull request potentially affect one of the following parts

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @public(Evolving) : no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable