Avro Schema Evolution Demystified: Backward and Forward Compatibility Explained
Avro is designed to support both backward and forward compatibility, making it a flexible and powerful choice for data serialization. Here’s an explanation of backward and forward compatibility in the context of Avro:Avro is designed to support both backward and forward compatibility, making it a flexible and powerful choice for data serialization. Here’s an explanation of backward and forward compatibility in the context of Avro:
Backward Compatibility:
Backward compatibility ensures that a new version of a schema can read data written in an older version of the schema. In other words, if you have data serialized with an older schema, it should be possible to deserialize and interpret that data using a newer version of the schema without encountering errors.
Common changes that maintain backward compatibility include:
1.Adding Fields:
- New fields are added to the schema with default values. Old data can be read without these fields, and default values will be used.
2. Removing Optional Fields:
- Optional fields (with default values) can be safely removed. Existing data will not have these fields, and default values will be assumed during deserialization.
3. Reordering Fields:
- Fields can be reordered without affecting compatibility, as Avro uses field names for serialization and deserialization.
Forward Compatibility:
Forward compatibility ensures that an older version of a schema can read data written in a newer version of the schema. This allows applications with an older schema to consume data produced by a newer schema.
Common changes that maintain forward compatibility include:
- Adding Optional Fields:
- New optional fields are added to the schema, and older consumers can ignore these fields.
2. Changing Field Types:
- If a field’s type is changed to a compatible type (e.g., from int to long), older consumers can still read the data.
3. Adding Enums or Symbols:
- New symbols or enums can be added to existing enums without breaking compatibility, as older consumers will treat unknown symbols as if they were the default.
Example:
Consider a simple example where you have an Avro schema for a user:
If you want to add a new optional field “email” to the schema, it remains backward-compatible because old data doesn’t have to include the “email” field, and new consumers can handle the absence of “email.”
{
"type": "record",
"name": "User",
"fields": [
{"name": "id", "type": "int"},
{"name": "name", "type": "string"},
{"name": "email", "type": ["null", "string"], "default": null}
]
}