# Topic

This schema defines the Topic entity. A topic is a feed into which message are published to by publishers and read from by consumers in a messaging service.

**$id:** [**https://open-metadata.org/schema/entity/data/topic.json**](https://open-metadata.org/schema/entity/data/topic.json)

Type: `object`

## Properties

* **id** `required`
  * Unique identifier that identifies this topic instance.
  * $ref: [../../type/basic.json\#/definitions/uuid](../types/basic.md#uuid)
* **name** `required`
  * Name that identifies the topic.
  * $ref: [\#/definitions/topicName](topic.md#topicname)
* **fullyQualifiedName**
  * Name that uniquely identifies a topic in the format 'messagingServiceName.topicName'.
  * Type: `string`
* **description**
  * Description of the topic instance.
  * Type: `string`
* **service** `required`
  * Link to the messaging cluster/service where this topic is hosted in.
  * $ref: [../../type/entityReference.json](../types/entityreference.md)
* **partitions** `required`
  * Number of partitions into which the topic is divided.
  * Type: `integer`
  * Range:  ≥ 1
* **schemaText**
  * Schema used for message serialization. Optional as some topics may not have associated schemas.
  * Type: `string`
* **schemaType**
  * Schema used for message serialization.
  * $ref: [\#/definitions/schemaType](topic.md#schematype)
* **cleanupPolicies**
  * Topic clean up policies. For Kafka - `cleanup.policy` configuration.
  * Type: `array`
    * **Items**
    * $ref: [\#/definitions/cleanupPolicy](topic.md#cleanuppolicy)
* **retentionTime**
  * Retention time in milliseconds. For Kafka - `retention.ms` configuration.
  * Type: `number`
* **maximumMessageSize**
  * Maximum message size in bytes. For Kafka - `max.message.bytes` configuration.
  * Type: `integer`
* **minimumInSyncReplicas**
  * Minimum number replicas in sync to control durability. For Kafka - `min.insync.replicas` configuration.
  * Type: `integer`
* **retentionSize**
  * Maximum size of a partition in bytes before old data is discarded. For Kafka - `retention.bytes` configuration.
  * Type: `number`
  * Default: _"-1"_
* **owner**
  * Owner of this topic.
  * $ref: [../../type/entityReference.json](../types/entityreference.md)
* **followers**
  * Followers of this table.
  * $ref: [../../type/entityReference.json\#/definitions/entityReferenceList](../types/entityreference.md#entityreferencelist)
* **tags**
  * Tags for this table.
  * Type: `array`
    * **Items**
    * $ref: [../../type/tagLabel.json](../types/taglabel.md)
* **href**
  * Link to the resource corresponding to this entity.
  * $ref: [../../type/basic.json\#/definitions/href](../types/basic.md#href)

## Type definitions in this schema

### topicName

* Name that identifies a topic.
* Type: `string`
* The value must match this pattern: `^[^.]*$`
* Length: between 1 and 64

### schemaType

* Schema type used for the message.
* The value is restricted to the following: 
  1. _"Avro"_
  2. _"Protobuf"_
  3. _"JSON"_
  4. _"Other"_

### cleanupPolicy

* Topic clean up policy. For Kafka - `cleanup.policy` configuration.
* The value is restricted to the following: 
  1. _"delete"_
  2. _"compact"_

_This document was updated on: Thursday, August 26, 2021_