An embedded SQL database written in Rust.

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Overview

Stoolap is an embedded SQL database with MVCC transactions, written entirely in Rust. It supports both in-memory and persistent storage modes with full ACID compliance.

Installation

# Add to Cargo.toml
[dependencies]
stoolap = "0.1"

Or build from source:

git clone https://github.com/stoolap/stoolap.git
cd stoolap
cargo build --release

Quick Start

As a Library

use stoolap::api::Database;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let db = Database::open_in_memory()?;

    db.execute("CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT)", ())?;
    db.execute("INSERT INTO users VALUES (1, 'Alice')", ())?;

    for row in db.query("SELECT * FROM users", ())? {
        let row = row?;
        println!("{}: {}", row.get::<i64>(0)?, row.get::<String>(1)?);
    }

    Ok(())
}

Command Line

./stoolap                                    # In-memory REPL
./stoolap --db "file:///path/to/data"        # Persistent database
./stoolap -q "SELECT 1 + 1"                  # Execute query directly

Features

MVCC Transactions

Full multi-version concurrency control with two isolation levels:

-- Read Committed (default)
BEGIN;
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
UPDATE accounts SET balance = balance + 100 WHERE id = 2;
COMMIT;

-- Snapshot Isolation
BEGIN TRANSACTION ISOLATION LEVEL SNAPSHOT;
SELECT * FROM accounts;  -- Consistent view throughout transaction
COMMIT;

Time-Travel Queries

Query historical data at any point in time:

-- Query data as it existed at a specific timestamp
SELECT * FROM orders AS OF TIMESTAMP '2024-01-15 10:30:00';

-- Query data as of a specific transaction
SELECT * FROM inventory AS OF TRANSACTION 1234;

-- Compare current vs historical data
SELECT
    current.price,
    historical.price AS old_price
FROM products current
JOIN products AS OF TIMESTAMP '2024-01-01' historical
    ON current.id = historical.id
WHERE current.price != historical.price;

Index Types

Stoolap automatically selects optimal index types, or you can specify explicitly:

-- B-tree: Range queries, sorting, prefix matching
CREATE INDEX idx_date ON orders(created_at) USING BTREE;
SELECT * FROM orders WHERE created_at BETWEEN '2024-01-01' AND '2024-12-31';

-- Hash: O(1) equality lookups
CREATE INDEX idx_email ON users(email) USING HASH;
SELECT * FROM users WHERE email = '[email protected]';

-- Bitmap: Low-cardinality columns, efficient AND/OR
CREATE INDEX idx_status ON orders(status) USING BITMAP;
SELECT * FROM orders WHERE status = 'pending' AND priority = 'high';

-- Multi-column composite indexes
CREATE INDEX idx_lookup ON events(user_id, event_type, created_at);
SELECT * FROM events WHERE user_id = 100 AND event_type = 'click';

Window Functions

Full support for analytical queries:

SELECT
    employee_name,
    department,
    salary,
    ROW_NUMBER() OVER (PARTITION BY department ORDER BY salary DESC) as rank,
    salary - LAG(salary) OVER (ORDER BY hire_date) as salary_change,
    AVG(salary) OVER (PARTITION BY department) as dept_avg,
    SUM(salary) OVER (ORDER BY hire_date ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) as running_total
FROM employees;

Common Table Expressions

Including recursive queries:

-- Non-recursive CTE
WITH high_value_orders AS (
    SELECT * FROM orders WHERE amount > 1000
)
SELECT customer_id, COUNT(*) FROM high_value_orders GROUP BY customer_id;

-- Recursive CTE (e.g., organizational hierarchy)
WITH RECURSIVE org_chart AS (
    SELECT id, name, manager_id, 1 as level
    FROM employees WHERE manager_id IS NULL

    UNION ALL

    SELECT e.id, e.name, e.manager_id, oc.level + 1
    FROM employees e
    JOIN org_chart oc ON e.manager_id = oc.id
)
SELECT * FROM org_chart ORDER BY level, name;

Advanced Aggregations

-- ROLLUP: Hierarchical subtotals
SELECT region, product, SUM(sales)
FROM sales_data
GROUP BY ROLLUP(region, product);

-- CUBE: All possible subtotal combinations
SELECT region, product, SUM(sales)
FROM sales_data
GROUP BY CUBE(region, product);

-- GROUPING SETS: Explicit grouping combinations
SELECT region, product, SUM(sales), GROUPING(region), GROUPING(product)
FROM sales_data
GROUP BY GROUPING SETS ((region, product), (region), ());

Subqueries

Scalar, correlated, EXISTS, and IN subqueries:

-- Correlated subquery
SELECT * FROM employees e
WHERE salary > (SELECT AVG(salary) FROM employees WHERE department = e.department);

-- EXISTS
SELECT * FROM customers c
WHERE EXISTS (SELECT 1 FROM orders o WHERE o.customer_id = c.id AND o.amount > 1000);

-- IN with subquery
SELECT * FROM products
WHERE category_id IN (SELECT id FROM categories WHERE active = true);

Query Optimizer

Cost-based optimizer with statistics:

-- Collect table statistics
ANALYZE orders;

-- View query execution plan
EXPLAIN SELECT * FROM orders WHERE customer_id = 100;

-- View plan with actual execution statistics
EXPLAIN ANALYZE SELECT * FROM orders o
JOIN customers c ON o.customer_id = c.id
WHERE c.country = 'US';

Data Types

Type	Description	Example
INTEGER	64-bit signed integer	42, -100
FLOAT	64-bit floating point	3.14, -0.001
TEXT	UTF-8 string	'hello', '日本語'
BOOLEAN	true/false	TRUE, FALSE
TIMESTAMP	Date and time	'2024-01-15 10:30:00'
JSON	JSON data	'{"key": "value"}'

Built-in Functions

String Functions

UPPER, LOWER, LENGTH, TRIM, LTRIM, RTRIM, CONCAT, SUBSTRING, REPLACE, REVERSE, LEFT, RIGHT, LPAD, RPAD, REPEAT, POSITION, LOCATE, INSTR, SPLIT_PART, INITCAP, ASCII, CHR, TRANSLATE

Math Functions

ABS, CEIL, FLOOR, ROUND, TRUNC, SQRT, POWER, MOD, SIGN, GREATEST, LEAST, EXP, LN, LOG, LOG10, LOG2, SIN, COS, TAN, ASIN, ACOS, ATAN, ATAN2, DEGREES, RADIANS, PI, RAND, RANDOM

Date/Time Functions

NOW, CURRENT_DATE, CURRENT_TIME, CURRENT_TIMESTAMP, EXTRACT, DATE_TRUNC, DATE_ADD, DATE_SUB, DATEDIFF, YEAR, MONTH, DAY, HOUR, MINUTE, SECOND, DAYOFWEEK, DAYOFYEAR, WEEK, QUARTER, TO_CHAR, TO_DATE, TO_TIMESTAMP

JSON Functions

JSON_EXTRACT, JSON_EXTRACT_PATH, JSON_TYPE, JSON_TYPEOF, JSON_VALID, JSON_KEYS, JSON_ARRAY_LENGTH

Aggregate Functions

COUNT, SUM, AVG, MIN, MAX, STDDEV, STDDEV_POP, STDDEV_SAMP, VARIANCE, VAR_POP, VAR_SAMP, STRING_AGG, ARRAY_AGG, FIRST, LAST, BIT_AND, BIT_OR, BIT_XOR, BOOL_AND, BOOL_OR

Window Functions

ROW_NUMBER, RANK, DENSE_RANK, NTILE, LAG, LEAD, FIRST_VALUE, LAST_VALUE, NTH_VALUE, PERCENT_RANK, CUME_DIST

Other Functions

COALESCE, NULLIF, CAST, CASE, IF, IIF, NVL, NVL2, DECODE, GREATEST, LEAST, GENERATE_SERIES

Persistence

Stoolap uses write-ahead logging (WAL) with periodic snapshots:

# In-memory (default) - data lost on exit
./stoolap --db "memory://"

# File-based - durable storage
./stoolap --db "file:///var/lib/stoolap/data"

Features:

• WAL: All changes logged before applied, survives crashes
• Snapshots: Periodic full database snapshots for faster recovery
• Index persistence: All indexes saved and restored

Architecture

src/
├── api/        # Public API (Database, Connection, Rows)
├── core/       # Types (Value, Row, Schema, Error)
├── parser/     # SQL lexer and parser
├── planner/    # Query planning
├── optimizer/  # Cost-based query optimizer
├── executor/   # Query execution engine
├── functions/  # 100+ built-in functions
│   ├── scalar/     # String, math, date, JSON
│   ├── aggregate/  # COUNT, SUM, AVG, etc.
│   └── window/     # ROW_NUMBER, RANK, LAG, etc.
└── storage/    # Storage engine
    ├── mvcc/       # Multi-version concurrency control
    └── index/      # B-tree, Hash, Bitmap indexes

Building

cargo build              # Debug build
cargo build --release    # Release build (optimized)
cargo test               # Run tests
cargo clippy             # Lint
cargo doc --open         # Generate documentation

Performance

See BENCHMARKS.md for detailed performance comparisons with SQLite.

Contributing

See CONTRIBUTING.md for guidelines.

License

Apache License 2.0. See LICENSE.