Topic Configuration

Topic-level configuration is dynamic config: read and written over the standard Kafka protocol, persisted in the meta layer, no restart needed. Unlike Broker Runtime Configuration (static, process-level), it applies to an individual topic.

How to read/write

Operation	Kafka API	CLI example
Read	DescribeConfigs	kafka-configs.sh --describe --entity-type topics --entity-name <topic>
Full alter	AlterConfigs	kafka-configs.sh --alter --entity-type topics --entity-name <topic> --add-config k=v
Incremental alter	IncrementalAlterConfigs	same as above (recent kafka-configs.sh uses incremental by default)
Set on create	CreateTopics --config	kafka-topics.sh --create --topic <topic> --config k=v

Keys passed via --config at create time are persisted too and can later be echoed back by --describe.

Supported standard keys

The following standard Kafka topic config keys can be stored and echoed back correctly:

Key	Description
retention.ms	Message retention time
cleanup.policy	Cleanup policy (delete / compact)
compression.type	Compression type
max.message.bytes	Max size of a single batch
retention.bytes	Max retained bytes per partition
segment.bytes	Segment size
Other standard keys	Stored and echoed

Status and limitations

Current implementation status

Topic config today behaves as "storable, echoable, with correct dynamic-source marking", but most keys are not yet fully wired into engine behavior:

• A written config is persisted, and DescribeConfigs echoes it back with the correct dynamic source marking (dynamic topic config).
• However, the value does not necessarily change actual engine behavior yet. For example, retention.ms is only partially applied; cleanup.policy=compact, compression.type, etc. are mostly not enforced in the storage engine yet.
• Think of topic config as "metadata first": the API and echo are ready; behavior enforcement is being filled in incrementally.

Config enforcement is on the Roadmap.

Relationship to broker config

max.message.bytes has both a broker-level default (kafka_runtime.max_message_bytes, see Broker Configuration) and a topic-level override. Cluster-level switches (e.g. auto.create.topics.enable) are a separate category, see Dynamic Configuration.