What is protobuf? What happens when adding/removing a field?

Protocol Buffers (protobuf) is a compact, efficient, and cross-platform data serialization format developed by Google. It allows describing data structures in .proto files and automatically generating code for various programming languages.

When adding a new field to a protobuf message:

• The new field must have a unique number (tag).
• Old clients that do not know about the new field simply ignore it, ensuring backward compatibility.

When removing a field:

• You cannot simply delete the field number, as this may lead to conflicts during deserialization.
• Usually, the field is marked as "deprecated" and no longer used, but the field number is not reused.

Thus, protobuf supports schema evolution without breaking compatibility between different service versions.