CODEWITHSUNDEEP
apache-kafkaconfluent-schema-registry
Ihor M.
Ihor M.

Reputation: 3148

Confluent Schema Registry "subjects" and "versions"

I am learning about Confluent's Schema Registry for all Schema management needs.

And I do not quite understand their approach to versioning... There is a notion of a subject, which I see as a namespace. As far as I understand subject must be unique across Schema Registry.

Then there is schema id, or just id, which is also unique.

And, finally, there is a version.

Here is the snippet from documentation:

version: the schema version for this subject, which starts at 1 for each subject

id: the globally unique schema version id, unique across all schemas in all subjects

So, once I want to modify a schema under a particular subject, what happens to id and version fields? Does id change? Does the version get incremented?

Another quote:

When schemas evolve, they are still associated to the same subject but get a new schema ID and version

Does every change warrant a new id and a new version?

Upvotes: 1

Views: 1809

Answers (1)

OneCricketeer
OneCricketeer

Reputation: 191973

Every subject has a list of versions. You can verify this in the source code, if you wish.

Every id in the Registry is globally unique, not ids within the "list of subject versions". There's only an incremental number of versions, per subject, stored based on the compatibility mode of the registry and this is an index, not a proper ID.

If two subjects share the same schema, the schema ID is the same, although the "version index" within two different subjects could be different. See example below for this case.

Every unique schema (as defined by it's textual representation) has a unique (possibly incremental) ID. They are MD5-hashed, or "fingerprinted" for uniqueness, then globally compared to one another across a Schema Registry cluster. This is done with the equivalent of ConcurrentHashMap<String, Schema> where the key is the hash of the value Schema object

example: Use sub, v, and s for subject, version and schema

  1. Create sub1, that makes v1:s1
  2. Update it to create v2:s2
  3. Take that updated schema text and POST it to a new sub2

sub1 : [ v1:s1, v2:s2 ]
sub2 : [ v1:s2 ]

Regarding the question

want to modify a schema under a particular subject, what happens to id and version fields? Does id change? Does the version get incremented?

The version will always be incremented if you make a compatible schema change. If your edit to the subject schema happens to match some other subject schema definition, then the ID wouldn't change

Upvotes: 2

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