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#28 in Database implementations

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Used in 4 crates




PliantDb is considered experimental and unsupported crate version Live Build Status HTML Coverage Report for main branch Documentation for main branch

PliantDb aims to be a Rust-written, ACID-compliant, document-database inspired by CouchDB. While it is inspired by CouchDB, this project will not aim to be compatible with existing CouchDB servers, and it will be implementing its own replication, clustering, and sharding strategies.

Project Goals

The high-level goals for this project are:

  • ☑️ Be able to build a document-based database's schema using Rust types.
  • ☑️ Run within your Rust binary, simplifying basic deployments.
  • ☑️ Run as a local-only file-based database with no networking involved.
  • ☑️ Run as a networked server using QUIC with TLS enabled by default
  • Easily set up read-replicas between multiple servers.
  • Easily run a highly-available quorum-based cluster across at least 3 servers
  • ☑️ Expose a Publish/Subscribe eventing system
  • Expose a Job queue and scheduling system -- a la Sidekiq or SQS

⚠️ Status of this project

You should not attempt to use this software in anything except for experiments. This project is under active development (GitHub commit activity), but at the point of writing this README, the project is too early to be used.

If you're interested in chatting about this project or potentially wanting to contribute, come chat with us on Discord: Discord.


Check out ./pliantdb/examples for examples. To get an idea of how it works, this is a simple schema:

#[derive(Debug, Serialize, Deserialize)]
struct Shape {
    pub sides: u32,

impl Collection for Shape {
    fn collection_name() -> Result<CollectionName, InvalidNameError> {
        CollectionName::new("khonsulabs", "shapes")

    fn define_views(schema: &mut Schematic) -> Result<(), Error> {

struct ShapesByNumberOfSides;

impl View for ShapesByNumberOfSides {
    type Collection = Shape;

    type Key = u32;

    type Value = usize;

    fn version(&self) -> u64 {

    fn name(&self) -> Result<Name, InvalidNameError> {

    fn map(&self, document: &Document<'_>) -> MapResult<Self::Key, Self::Value> {
        let shape = document.contents::<Shape>()?;
        Ok(Some(document.emit_key_and_value(shape.sides, 1)))

    fn reduce(
        mappings: &[MappedValue<Self::Key, Self::Value>],
        _rereduce: bool,
    ) -> Result<Self::Value, view::Error> {
        Ok(mappings.iter().map(|m| m.value).sum())

After you have your collection(s) defined, you can open up a database and insert documents:

    let db =
        Database::<Shape>::open_local("view-examples.pliantdb", &Configuration::default()).await?;

    // Insert a new document into the Shape collection.

And query data using the Map-Reduce-powered view:

let triangles = db
println!("Number of triangles: {}", triangles.len());

Why write another database?

  • Deploying highly-available databases is hard (and often expensive). It doesn't need to be.
  • We are passionate Rustaceans and are striving for an ideal of supporting a 100% Rust-based deployment ecosystem for newly written software.
  • Specifically for the founding author @ecton, the idea for this design dates back to thoughts of fun side-projects while running my last business which was built atop CouchDB. Working on this project is fulfilling a long-time desire of his.
let triangles = db
println!("Number of triangles: {}", triangles.len());

Feature Flags

No feature flags are enabled by default in the pliantdb crate. This is because in most Rust executables, you will only need a subset of the functionality. If you'd prefer to enable everything, you can use the full feature:

pliantdb = { version = "*", default-features = false, features = "full" }
  • full: Enables local-full, server-full, and client-full.
  • cli: Enables the pliantdb executable.

Local databases only

pliantdb = { version = "*", default-features = false, features = "local-full" }
  • local-full: Enables local, local-cli, local-keyvalue, and local-pubsub
  • local: Enables the local module, which re-exports the crate pliantdb-local.
  • local-cli: Enables the StructOpt structures for embedding database management commands into your own command-line interface.
  • local-pubsub: Enables PubSub for pliantdb-local.
  • local-keyvalue: Enables the key-value store for pliantdb-local.

PliantDb server

pliantdb = { version = "*", default-features = false, features = "server-full" }
  • server-full: Enables server, server-websockets, server-keyvalue, and server-pubsub
  • server: Enables the server module, which re-exports the crate pliantdb-server.
  • server-websockets: Enables WebSocket support for pliantdb-server.
  • server-pubsub: Enables PubSub for pliantdb-server.
  • server-keyvalue: Enables the key-value store for pliantdb-server.

Client for accessing a PliantDb server

pliantdb = { version = "*", default-features = false, features = "client-full" }
  • client-full: Enables client, client-trusted-dns, client-websockets, client-keyvalue, and client-pubsub
  • client: Enables the client module, which re-exports the crate pliantdb-client.
  • client-trusted-dns: Enables using trust-dns for DNS resolution. If not enabled, all DNS resolution is done with the OS's default name resolver.
  • client-websockets: Enables WebSocket support for pliantdb-client.
  • client-pubsub: Enables PubSub for pliantdb-client.
  • client-keyvalue: Enables the key-value store for pliantdb-client.


Exporting and restoring databases with direct access

If you have a local PliantDb database, you can use the local-backup command to save and load backups:

pliantdb local-backup <database-path> save
pliantdb local-backup <destination-database-path> load <backup-path>

The format of this export should be easy to work with if you're either transitioning from PliantDb to another solution or needing to do complicated disaster recovery work. It is described here.

Developing PliantDb

Pre-commit hook

Our CI processes require that some commands succeed without warnings or errors. To ensure that code you submit passes the basic checks, install the included pre-commit hook:

./git-pre-commit-hook.sh install

Once done, tools including cargo fmt, cargo doc, and cargo test will all be checked before git commit will execute.

Open-source Licenses

This project, like all projects from Khonsu Labs, are open-source. This repository is available under the MIT License or the Apache License 2.0.


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