Module ondisk

Database

Database is a lightweight, single append-only file, key-value store designed as an alternative to RocksDB.

Storage Format

Each entry in the Database has the following structure:

+------------+-----------+-----------+
|    HDR     |    KEY    |   VALUE   |
| (17 bytes) | (X bytes) | (X bytes) |
+------------+-----------+-----------+
      ^
      |
      |
+------------+--------------+-----------+------------+
| KEY_LENGTH | VALUE_LENGTH | BITFLAGS  |   CRC32    |
| (4 bytes)  | (8 bytes)    | (1 byte)  | (4 bytes)  |
+------------+--------------+-----------+------------+

Where:

• HDR: A 17 bytes header
  • KEY_LENGTH: Length of the key, stored in 4 bytes.
  • VALUE_LENGTH: Length of the value, stored in 8 bytes.
  • BITFLAGS: A 1 byte bitflags including:
    • key_is_compressed: A flag indicating if the key is compressed.
    • value_is_compressed: A flag indicating if the value is compressed.
    • is_removed: A flag indicating if the entry has been removed.
  • CRC32: The CRC32 checksum of the entry (including its header), stored in 4 bytes.
• KEY: The key data
• VALUE: The value data

Example Usage

Create an instance of MyDatabase:

let mut db = Database::create("/tmp/my_database")?;

// Insert a key-value pair:
db.set(k("key1"), v("value1"))?;

// Retrieve a value by key:
let result = db.get(&k("key1"))?;
assert_eq!(result, Some(v("value1")));

Re-exports

pub use batch::Batch;

Modules

batch

compression 🔒

database 🔒

lock 🔒

Structs

Database

Type Aliases

Uuid