Manage schema

This guide demonstrates the ways to manage schemas:

• Automatically

  • Schema AutoUpdate

• Manually

  • Schema manual management

  • Custom schema storage

Schema AutoUpdate

If a schema passes the schema compatibility check, Pulsar producer automatically updates this schema to the topic it produces by default.

AutoUpdate for producer

For a producer, the AutoUpdate happens in the following cases:

• If a topic doesn’t have a schema, Pulsar registers a schema automatically.

• If a topic has a schema:

  • If a producer doesn’t carry a schema:

  • If isSchemaValidationEnforced or schemaValidationEnforced is disabled in the namespace to which the topic belongs, the producer is allowed to connect to the topic and produce data.

  • If isSchemaValidationEnforced or schemaValidationEnforced is enabled in the namespace to which the topic belongs, the producer is rejected and disconnected.

  • If a producer carries a schema:

  A broker performs the compatibility check based on the configured compatibility check strategy of the namespace to which the topic belongs.

  • If the schema is registered, a producer is connected to a broker.

  • If the schema is not registered:

    • If isAllowAutoUpdateSchema sets to false, the producer is rejected to connect to a broker.

    • If isAllowAutoUpdateSchema sets to true:

      • If the schema passes the compatibility check, then the broker registers a new schema automatically for the topic and the producer is connected.

      • If the schema does not pass the compatibility check, then the broker does not register a schema and the producer is rejected to connect to a broker.

AutoUpdate for consumer

For a consumer, the AutoUpdate happens in the following cases:

• If a consumer connects to a topic without a schema (which means the consumer receiving raw bytes), the consumer can connect to the topic successfully without doing any compatibility check.

• If a consumer connects to a topic with a schema.

  • If a topic does not have all of them (a schema/data/a local consumer and a local producer):

    • If isAllowAutoUpdateSchema sets to true, then the consumer registers a schema and it is connected to a broker.

    • If isAllowAutoUpdateSchema sets to false, then the consumer is rejected to connect to a broker.

  • If a topic has one of them (a schema/data/a local consumer and a local producer), then the schema compatibility check is performed.

    • If the schema passes the compatibility check, then the consumer is connected to the broker.

    • If the schema does not pass the compatibility check, then the consumer is rejected to connect to the broker.

Manage AutoUpdate strategy

You can use the pulsar-admin command to manage the AutoUpdate strategy as below:

• Enable AutoUpdate

• Disable AutoUpdate

• Adjust compatibility

Enable AutoUpdate

To enable AutoUpdate on a namespace, you can use the pulsar-admin command.

bin/pulsar-admin namespaces set-is-allow-auto-update-schema --enable tenant/namespace

Disable AutoUpdate

To disable AutoUpdate on a namespace, you can use the pulsar-admin command.

bin/pulsar-admin namespaces set-is-allow-auto-update-schema --disable tenant/namespace

Once the AutoUpdate is disabled, you can only register a new schema using the pulsar-admin command.

Adjust compatibility

To adjust the schema compatibility level on a namespace, you can use the pulsar-admin command.

bin/pulsar-admin namespaces set-schema-compatibility-strategy --compatibility <compatibility-level> tenant/namespace

Schema validation

By default, schemaValidationEnforced is disabled for producers:

• This means a producer without a schema can produce any kind of messages to a topic with schemas, which may result in producing trash data to the topic.

• This allows non-java language clients that don’t support schema can produce messages to a topic with schemas.

However, if you want a stronger guarantee on the topics with schemas, you can enable schemaValidationEnforced across the whole cluster or on a per-namespace basis.

Enable schema validation

To enable schemaValidationEnforced on a namespace, you can use the pulsar-admin command.

bin/pulsar-admin namespaces set-schema-validation-enforce --enable tenant/namespace

Disable schema validation

To disable schemaValidationEnforced on a namespace, you can use the pulsar-admin command.

bin/pulsar-admin namespaces set-schema-validation-enforce --disable tenant/namespace

Schema manual management

To manage schemas, you can use one of the following methods.

Method	Description
Admin CLI	You can use the pulsar-admin tool to manage Pulsar schemas, brokers, clusters, sources, sinks, topics, tenants and so on. For more information about how to use the pulsar-admin tool, see here.
REST API	Pulsar exposes schema related management API in Pulsar’s admin RESTful API. You can access the admin RESTful endpoint directly to manage schemas. For more information about how to use the Pulsar REST API, see here.
Java Admin API	Pulsar provides Java admin library.

Upload a schema

To upload (register) a new schema for a topic, you can use one of the following methods.

Admin CLI

Use the upload subcommand.

$ pulsar-admin schemas upload --filename <schema-definition-file> <topic-name>

The schema-definition-file is in JSON format.

{
    "type": "<schema-type>",
    "schema": "<an-utf8-encoded-string-of-schema-definition-data>",
    "properties": {} // the properties associated with the schema
}

The schema-definition-file includes the following fields:

Field	Description
type	The schema type.
schema	The schema definition data, which is encoded in UTF 8 charset. If the schema is a primitive schema, this field should be blank. If the schema is a struct schema, this field should be a JSON string of the Avro schema definition.
properties	The additional properties associated with the schema.

Here are examples of the schema-definition-file for a JSON schema.

Example 1

{
    "type": "JSON",
    "schema": "{\"type\":\"record\",\"name\":\"User\",\"namespace\":\"com.foo\",\"fields\":[{\"name\":\"file1\",\"type\":[\"null\",\"string\"],\"default\":null},{\"name\":\"file2\",\"type\":\"string\",\"default\":null},{\"name\":\"file3\",\"type\":[\"null\",\"string\"],\"default\":\"dfdf\"}]}",
    "properties": {}
}

Example 2

{
    "type": "STRING",
    "schema": "",
    "properties": {
        "key1": "value1"
    }
}

REST API

Send a POST request to this endpoint: POST /admin/v2/schemas/:tenant/:namespace/:topic/schema/uploadSchema

The post payload is in JSON format.

{
    "type": "<schema-type>",
    "schema": "<an-utf8-encoded-string-of-schema-definition-data>",
    "properties": {} // the properties associated with the schema
}

The post payload includes the following fields:

Field	Description
type	The schema type.
schema	The schema definition data, which is encoded in UTF 8 charset. If the schema is a primitive schema, this field should be blank. If the schema is a struct schema, this field should be a JSON string of the Avro schema definition.
properties	The additional properties associated with the schema.

Java Admin API

void createSchema(String topic, PostSchemaPayload schemaPayload)

The PostSchemaPayload includes the following fields:

Field	Description
type	The schema type.
schema	The schema definition data, which is encoded in UTF 8 charset. If the schema is a primitive schema, this field should be blank. If the schema is a struct schema, this field should be a JSON string of the Avro schema definition.
properties	The additional properties associated with the schema.

Here is an example of PostSchemaPayload:

PulsarAdmin admin = …;

PostSchemaPayload payload = new PostSchemaPayload();
payload.setType("INT8");
payload.setSchema("");

admin.createSchema("my-tenant/my-ns/my-topic", payload);

Get a schema (latest)

To get the latest schema for a topic, you can use one of the following methods.

Admin CLI

Use the get subcommand.

$ pulsar-admin schemas get <topic-name>

{
    "version": 0,
    "type": "String",
    "timestamp": 0,
    "data": "string",
    "properties": {
        "property1": "string",
        "property2": "string"
    }
}

REST API

Send a GET request to this endpoint: GET /admin/v2/schemas/:tenant/:namespace/:topic/schema/getSchema

Here is an example of a response, which is returned in JSON format.

{
    "version": "<the-version-number-of-the-schema>",
    "type": "<the-schema-type>",
    "timestamp": "<the-creation-timestamp-of-the-version-of-the-schema>",
    "data": "<an-utf8-encoded-string-of-schema-definition-data>",
    "properties": {} // the properties associated with the schema
}

The response includes the following fields:

Field	Description
version	The schema version, which is a long number.
type	The schema type.
timestamp	The timestamp of creating this version of schema.
data	The schema definition data, which is encoded in UTF 8 charset. If the schema is a primitive schema, this field should be blank. If the schema is a struct schema, this field should be a JSON string of the Avro schema definition.
properties	The additional properties associated with the schema.

Java Admin API

SchemaInfo createSchema(String topic)

The SchemaInfo includes the following fields:

Field	Description
name	The schema name.
type	The schema type.
schema	A byte array of the schema definition data, which is encoded in UTF 8 charset. If the schema is a primitive schema, this byte array should be empty. If the schema is a struct schema, this field should be a JSON string of the Avro schema definition converted to a byte array.
properties	The additional properties associated with the schema.

Here is an example of SchemaInfo:

PulsarAdmin admin = …;

SchemaInfo si = admin.getSchema("my-tenant/my-ns/my-topic");

Get a schema (specific)

To get a specific version of a schema, you can use one of the following methods.

Admin CLI

Use the get subcommand.

$ pulsar-admin schemas get <topic-name> --version=<version>

REST API

Send a GET request to a schema endpoint: GET /admin/v2/schemas/:tenant/:namespace/:topic/schema/:version/getSchema

Here is an example of a response, which is returned in JSON format.

{
    "version": "<the-version-number-of-the-schema>",
    "type": "<the-schema-type>",
    "timestamp": "<the-creation-timestamp-of-the-version-of-the-schema>",
    "data": "<an-utf8-encoded-string-of-schema-definition-data>",
    "properties": {} // the properties associated with the schema
}

The response includes the following fields:

Field	Description
version	The schema version, which is a long number.
type	The schema type.
timestamp	The timestamp of creating this version of schema.
data	The schema definition data, which is encoded in UTF 8 charset. If the schema is a primitive schema, this field should be blank. If the schema is a struct schema, this field should be a JSON string of the Avro schema definition.
properties	The additional properties associated with the schema.

Java Admin API

SchemaInfo createSchema(String topic, long version)

The SchemaInfo includes the following fields:

Field	Description
name	The schema name.
type	The schema type.
schema	A byte array of the schema definition data, which is encoded in UTF 8. If the schema is a primitive schema, this byte array should be empty. If the schema is a struct schema, this field should be a JSON string of the Avro schema definition converted to a byte array.
properties	The additional properties associated with the schema.

Here is an example of SchemaInfo:

PulsarAdmin admin = …;

SchemaInfo si = admin.getSchema("my-tenant/my-ns/my-topic", 1L);

Extract a schema

To provide a schema via a topic, you can use the following method.

Admin CLI

Use the extract subcommand.

$ pulsar-admin schemas extract --classname <class-name> --jar <jar-path> --type <type-name>

Delete a schema

To delete a schema for a topic, you can use one of the following methods.

note

In any case, the delete action deletes all versions of a schema registered for a topic.

Admin CLI

Use the delete subcommand.

$ pulsar-admin schemas delete <topic-name>

REST API

Send a DELETE request to a schema endpoint: DELETE /admin/v2/schemas/:tenant/:namespace/:topic/schema/deleteSchema

Here is an example of a response, which is returned in JSON format.

{
    "version": "<the-latest-version-number-of-the-schema>",
}

The response includes the following field:

Field	Description
version	The schema version, which is a long number.

Java Admin API

void deleteSchema(String topic)

Here is an example of deleting a schema.

PulsarAdmin admin = …;

admin.deleteSchema("my-tenant/my-ns/my-topic");

Custom schema storage

By default, Pulsar stores various data types of schemas in Apache BookKeeper deployed alongside Pulsar.

However, you can use another storage system if needed.

Implement

To use a non-default (non-BookKeeper) storage system for Pulsar schemas, you need to implement the following Java interfaces:

• SchemaStorage interface

• SchemaStorageFactory interface

SchemaStorage interface

The SchemaStorage interface has the following methods:

public interface SchemaStorage {
    // How schemas are updated
    CompletableFuture<SchemaVersion> put(String key, byte[] value, byte[] hash);

    // How schemas are fetched from storage
    CompletableFuture<StoredSchema> get(String key, SchemaVersion version);

    // How schemas are deleted
    CompletableFuture<SchemaVersion> delete(String key);

    // Utility method for converting a schema version byte array to a SchemaVersion object
    SchemaVersion versionFromBytes(byte[] version);

    // Startup behavior for the schema storage client
    void start() throws Exception;

    // Shutdown behavior for the schema storage client
    void close() throws Exception;
}

tip

For a complete example of schema storage implementation, see BookKeeperSchemaStorage class.

SchemaStorageFactory interface

The SchemaStorageFactory interface has the following method:

public interface SchemaStorageFactory {
    @NotNull
    SchemaStorage create(PulsarService pulsar) throws Exception;
}

tip

For a complete example of schema storage factory implementation, see BookKeeperSchemaStorageFactory class.

Deploy

To use your custom schema storage implementation, perform the following steps.

1. Package the implementation in a JAR file.

2. Add the JAR file to the lib folder in your Pulsar binary or source distribution.

3. Change the schemaRegistryStorageClassName configuration in broker.conf to your custom factory class.

4. Start Pulsar.