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Version: 2.10.1

Manage schema

This guide demonstrates the ways to manage schemas:

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 Producer

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.

AutoUpdate Consumer

Manage AutoUpdate strategy​

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

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.

MethodDescription
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.

    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:

    FieldDescription
    typeThe schema type.
    schemaThe 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.
  • propertiesThe 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"
    }
    }

    Get a schema (latest)​

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

    Use the get subcommand.


    $ pulsar-admin schemas get <topic-name>

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

    Get a schema (specific)​

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

    Use the get subcommand.


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

    Extract a schema​

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

    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.

    Use the delete subcommand.


    $ pulsar-admin schemas delete <topic-name>

    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​

    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.

    Set schema compatibility check strategy​

    You can set schema compatibility check strategy at the topic, namespace or broker level.

    The schema compatibility check strategy set at different levels has priority: topic level > namespace level > broker level.

    • If you set the strategy at both topic and namespace level, it uses the topic-level strategy.

    • If you set the strategy at both namespace and broker level, it uses the namespace-level strategy.

    • If you do not set the strategy at any level, it uses the FULL strategy. For all available values, see here.

    Topic level​

    To set a schema compatibility check strategy at the topic level, use one of the following methods.

    Use the pulsar-admin topicPolicies set-schema-compatibility-strategy command.


    pulsar-admin topicPolicies set-schema-compatibility-strategy <strategy> <topicName>


    To get the topic-level schema compatibility check strategy, use one of the following methods.

    Use the pulsar-admin topicPolicies get-schema-compatibility-strategy command.


    pulsar-admin topicPolicies get-schema-compatibility-strategy <topicName>


    To remove the topic-level schema compatibility check strategy, use one of the following methods.

    Use the pulsar-admin topicPolicies remove-schema-compatibility-strategy command.


    pulsar-admin topicPolicies remove-schema-compatibility-strategy <topicName>

    Namespace level​

    You can set schema compatibility check strategy at namespace level using one of the following methods.

    Use the pulsar-admin namespaces set-schema-compatibility-strategy command.


    pulsar-admin namespaces set-schema-compatibility-strategy options

    Broker level​

    You can set schema compatibility check strategy at broker level by setting schemaCompatibilityStrategy in broker.conf or standalone.conf file.

    Example


    schemaCompatibilityStrategy=ALWAYS_INCOMPATIBLE