[Feature] [cdc] Avoid sending empty schema change events to Schema Evolution

[juntaozhang]

Search before asking

• I searched in the issues and found nothing similar.

Motivation

RichEventParser.parseSchemaChange() always returns a CdcSchema object even when there is no actual schema change. This causes empty schema change events to be sent to the Schema Evolution operator via side output, resulting in unnecessary network overhead and processing.

Solution

Return null from parseSchemaChange() when there is no schema change (no field changes and no comment changes). This is consistent with RichCdcMultiplexRecordEventParser which already returns null when the table
should not be synchronized.

Anything else?

after optimize:

Are you willing to submit a PR?

• I'm willing to submit a PR!