emqx4.3/apps/emqx_durable_storage/README.md

EMQX Replay

emqx_ds is an application implementing durable storage for MQTT messages within EMQX.

Features

• Streams. Stream is an abstraction that encompasses topics, shards, different data layouts, etc. The client application must only aware of the streams.

• Batching. All the API functions are batch-oriented.

• Iterators. Iterators can be stored durably or transferred over network. They take relatively small space.

• Support for various backends. Almost any DBMS that supports range queries can serve as a emqx_durable_storage backend.

• Builtin backend based on RocksDB.

  • Changing storage layout on the fly: it's achieved by creating a new set of tables (known as "generation") and the schema.
  • Sharding based on publisher's client ID

Limitation

• Builtin backend currently doesn't replicate data across different sites
• There is no local cache of messages, which may result in transferring the same data multiple times

Documentation links

TBD

Usage

Currently it's only used to implement persistent sessions.

In the future it can serve as a storage for retained messages or as a generic message buffering layer for the bridges.

Configurations

emqx_durable_storage doesn't have any configurable parameters. Instead, it relies on the upper-level business applications to create a correct configuration and pass it to emqx_ds:open_db(DBName, Config) function according to its needs.

HTTP APIs

None

Other

TBD

Contributing

Please see our contributing.md.