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Changelog category (leave one):

• New Feature

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):
Add setting to fields not found in Avro schema

Detailed description / Documentation draft:
Add setting input_format_avro_allow_missing_fields to allow reading fields not found in Avro schema (using default value instead).
Useful for Kafka + schema evolution when old messages are missing newly added field in their schema and preventing ClickHouse from making progress.
Related to #11986

Not using input_format_defaults_for_omitted_fields because it defaults to true.

By adding documentation, you'll allow users to try your new feature immediately, not when someone else will have time to document it later. Documentation is necessary for all features that affect user experience in any way. You can add brief documentation draft above, or add documentation right into your patch as Markdown files in docs folder.

If you are doing this for the first time, it's recommended to read the lightweight Contributing to ClickHouse Documentation guide first.