Database Project

A Rust-based database system with ACID transaction support, MVCC, and a client-server architecture.

Features

• ACID Transactions: Full transaction support with BEGIN, COMMIT, and ROLLBACK
• Isolation Levels: Read Committed and Repeatable Read isolation
• MVCC: Multi-Version Concurrency Control for snapshot isolation
• Write-Ahead Logging: ARIES-style WAL with checkpoints, compensation log records (CLRs), and 3-phase crash recovery (Analysis, Redo, Undo)
• B-Tree Index: Efficient key-value storage and retrieval
• TCP Protocol: Binary protocol for client-server communication
• Interactive CLI: Command-line client with tab completion

Project Structure

.
├── backend/              # Database server implementation
│   └── src/
│       ├── btree/        # B-tree index implementation
│       ├── command/      # Command parsing and types
│       ├── database_handler/  # Database operations
│       ├── protocol/     # Network protocol (frames, connections)
│       ├── server/       # TCP server and request handling
│       ├── storage/      # Storage engine
│       │   ├── buffer_pool.rs   # In-memory page cache
│       │   ├── disk_manager.rs  # Disk I/O
│       │   ├── mvcc.rs          # Multi-version concurrency control
│       │   ├── transaction.rs   # Transaction and snapshot management
│       │   ├── wal.rs           # Write-ahead logging
│       │   └── value.rs         # Value types
│       └── tests/        # Unit tests
└── database-client/      # Interactive CLI client

Getting Started

# Build the project
cargo build

# Start the server (default port: 5432)
cargo run --bin server

# In another terminal, start the client
cargo run --package database-client

Commands

Basic Operations

Command	Description
GET <key>	Retrieve value by key
SET <key> <value>	Store a key-value pair
UPDATE <key> <value>	Update existing value
DEL <key>	Delete a key-value pair
ALL	List all key-value pairs

String Operations

Command	Description
STRLEN <key>	Get string length
STRCAT <key> <value>	Append to string value
SUBSTR <key> <start> <len>	Extract substring

Transaction Commands

Command	Description
BEGIN [isolation]	Start transaction (returns txn_id)
COMMIT	Commit current transaction
ROLLBACK	Abort current transaction

Isolation levels: read_committed or rc (default), repeatable_read or rr

Maintenance Commands

Command	Description
VACUUM	Run garbage collection on old versions
PING	Test server connectivity

Transactional Operations

Commands can be executed within a transaction using the TXN <id> suffix:

BEGIN rr                 # Returns: 1 (RepeatableRead isolation)
SET 1 100 TXN 1          # Insert within transaction
SET 2 200 TXN 1          # Another insert
GET 1 TXN 1              # Read within transaction (sees own writes)
ALL TXN 1                # List all within transaction snapshot
COMMIT                   # Commit all changes

Read commands that support transaction context:

• GET <key> [TXN <id>]
• ALL [TXN <id>]
• STRLEN <key> [TXN <id>]

Expression Evaluation

EXPR(GET 1 + GET 2)      # Add values of key 1 and 2
SET 3 EXPR(GET 1 * 2)    # Set key 3 to double of key 1
EXPR(GET 1 + 3.14)       # Mix keys and literals

Architecture

┌─────────────────────────────────────────────────────────────┐
│                      Client Layer                            │
│              TCP Connection + Binary Protocol                │
└─────────────────────────────────────────────────────────────┘
                            │
┌─────────────────────────────────────────────────────────────┐
│                   Transaction Layer                          │
│  ┌─────────────┐ ┌──────────────┐ ┌──────────────────────┐  │
│  │ Isolation   │ │   Snapshot   │ │ Transaction Manager  │  │
│  │ RC/RR/Ser   │ │  Visibility  │ │   Active/Committed   │  │
│  └─────────────┘ └──────────────┘ └──────────────────────┘  │
└─────────────────────────────────────────────────────────────┘
                            │
┌─────────────────────────────────────────────────────────────┐
│                      MVCC Layer                              │
│         VersionedValue { value, xmin, xmax }                 │
└─────────────────────────────────────────────────────────────┘
                            │
┌─────────────────────────────────────────────────────────────┐
│                    Storage Layer                             │
│  B-Tree Index → Buffer Pool → Disk Manager → WAL            │
└─────────────────────────────────────────────────────────────┘

MVCC (Multi-Version Concurrency Control)

The database uses MVCC to provide snapshot isolation:

• Version Tracking: Each value stores xmin (creating transaction) and xmax (deleting transaction)
• Visibility Rules: Transactions only see versions created by committed transactions before their snapshot
• No Read Locks: Readers never block writers; writers never block readers
• Garbage Collection: Use VACUUM to clean up old versions no longer visible to any transaction

Isolation Levels

Level	Description
Read Committed (rc)	Each statement sees latest committed data
Repeatable Read (rr)	Transaction sees consistent snapshot from start

Example: Repeatable Read Isolation

# Terminal 1                    # Terminal 2
BEGIN rr                        
GET 1                           # Returns: 100
                                UPDATE 1 200
                                COMMIT
GET 1                           # Still returns: 100 (snapshot)
COMMIT
GET 1                           # Now returns: 200

Development

# Run all tests
cargo test

# Run specific test module
cargo test btree_tests
cargo test transaction_tests
cargo test mvcc_tests

# Run a single test
cargo test test_btree_operations -- --exact

# Format code
cargo fmt

# Run linter
cargo clippy

Value Types

The database supports multiple value types:

• Integer(i64) - 64-bit signed integers
• Float(f64) - 64-bit floating point
• String(String) - UTF-8 strings
• Boolean(bool) - true/false
• Null - null value

Configuration

Currently hardcoded defaults (configuration file support planned):

Setting	Default
Server port	5432
Buffer pool size	1000 pages
Page size	4KB
Thread pool size	4

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

See LICENSE file.