apllodb

apllodb is a RDBMS purely written in Rust.

It has the following distinguished features:

• Plugable storage engine:
  • Implementing apllodb’s storage engine is unambiguous. Your storage engine crate just depends on apllodb-storage-engine-interface crate and implements StorageEngine trait (and its associated types).
  • apllodb’s default storage engine is Immutable Schema Engine (apllodb-immutable-schema-engine). This engine never deletes / requires to delete old records on UPDATE, DELETE, even on ALTER TABLE and DROP TABLE.

Also, we have plan to develop the following unique features:

• Ambiguous data (“about 100 years ago”, for example) and query toward them.
• Algebraic data type as SQL types.

Getting Started

Here shows how to build & run apllodb-cli and execute simple SQLs.

You are supposed to have installed Cargo.

git clone git@github.com:eukarya-inc/apllodb.git
cd apllodb
cargo build
./target/debug/apllodb-cli
🚀🌙 SQL>   # Press Ctrl-D to exit

🚀🌙 SQL> create database my_db;
🚀🌙 SQL> use database my_db;
🚀🌙 SQL> create table t (id integer, name text, primary key (id));
  -- Oops! You need open transaction even for DDL.
🚀🌙 SQL> begin;
🚀🌙 SQL> create table t (id integer, name text, primary key (id));
🚀🌙 SQL> select id, name from t;
0 records in total
🚀🌙 SQL> insert into t (id, name) values (1, "name 1");
🚀🌙 SQL> insert into t (id, name) values (2, "name 2");
🚀🌙 SQL> select id, name from t;
t.id: 2 t.name: "name 2"
t.id: 1 t.name: "name 1"
2 records in total
🚀🌙 SQL> commit;

Try Immutable Schema

Current core feature of apllodb is Immutable Schema.
Immutable Schema consists of Immutable DDL and Immutable DML.

With Immutable DDL, any kind of ALTER TABLE or DROP TABLE succeed without modifying existing records.
For example, if t has 1 or more records,

ALTER TABLE t ADD COLUMN c_new INTEGER NOT NULL;

would cause error in many RDMBSs because existing records cannot be NULL but this ALTER does not specify default value for c_new.

Immutable Schema preserves existing records in an old version and creates new version.

 t (version1)
| id | c_old |
|----|-------|
|  1 | "a"   |
|  2 | "b"   |
ALTER TABLE t ADD COLUMN c_new INTEGER NOT NULL;
 t (version1)    t (version2) 
| id | c_old |  | id | c_old | c_new |
|----|-------|  |----|-------|-------|
|  1 | "a"   |
|  2 | "b"   |
INSERT INTO t (id, c_old, c_new) VALUES (3, "c", 42);
 t (version1)    t (version2) 
| id | c_old |  | id | c_old | c_new |
|----|-------|  |----|-------|-------|
|  1 | "a"   |  |  3 |   "c" |    42 |
|  2 | "b"   |
INSERT INTO t (id, c_old) VALUES (4, "d");
 t (version1)    t (version2) 
| id | c_old |  | id | c_old | c_new |
|----|-------|  |----|-------|-------|
|  1 | "a"   |  |  3 |   "c" |    42 |
|  2 | "b"   |
|  4 | "d"   |

As the above example shows, DML like INSERT automatically choose appropriate version to modify.

To learn more about Immutable Schema, check this slide (Japanese version).

Currently, both Immutable DDL and Immutable DML are under development and some SQLs do not work as expected.
doc/immutable-ddl-demo.sql is a working example of Immutable DDL. Try it by copy-and-paste to apllodb-cli.

Development

This repository is a multi-package project.

Many useful tasks for development are defined in Makefile.toml. Install cargo-make to participate in apllodb’s development.

# (clone repository)
cd apllodb
cargo make test
# (write your code)
cargo make build
cargo make test
# (before making pull-request)
cargo make format
cargo make lint
# (generate rustdoc)
cargo make doc

Architecture

We refer to “Architecture of a Database System” to set boundaries between each components (crates).

The following diagram, similarly illustrated to Fig. 1.1 of the paper, shows sub-crates and their rolls.
(Box with gray text are unimplemented roles)

Entry points in apllodb-server, apllodb-sql-processor, and apllodb-storage-engine-interface are async functions so clients can run multiple SQLs at a time.

apllodb-server is the component to choose storage engine to use. apllodb-immutable-schema-engine::ApllodbImmutableSchemaEngine is specified at compile-time (as type parameter) for now.

Currently, apllodb has a single client; apllodb-cli. apllodb-cli runs from a shell, takes SQL text from stdin, and outputs query result records (or error messages) to stdout/stderr.
Also, apllodb-cli works as single-process database. apllodb-server currently does not run solely.

Of course we have plan to:

• Split server and client.
• Provides client library for programming languages (Rust binding may be the first one).

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in apllodb by you, as defined in the Apache-2.0 license, shall be
dual licensed as above, without any additional terms or conditions.