Challenge 6a: Single-Node Transactions

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Built transactional operations on a single node with full ACID guarantees. This is where we start building real database-like features.

What it Does

• Transactions: Atomic read/write operations

• Isolation: Transactions don't interfere with each other

• Consistency: Operations maintain data integrity

• Durability: Committed transactions persist

The Implementation

• In-memory transaction log

• Version-based concurrency control

• Atomic commit/rollback semantics

• Simple two-phase transaction protocol

Transaction Operations

• Begin: Start a new transaction

• Read: Read values within transaction context

• Write: Buffer writes until commit

• Commit: Apply all buffered writes atomically

• Rollback: Discard all transaction changes

Key Design Choices

• Optimistic Concurrency: Assume no conflicts initially

• Version Vectors: Track read/write sets for conflict detection

• Local Atomicity: Single-node makes commit simple

• Write Buffering: Defer writes until commit

ACID Properties

1. Atomicity: All operations in transaction succeed or fail together

2. Consistency: Transactions maintain data invariants

3. Isolation: Concurrent transactions don't interfere

4. Durability: Committed changes persist

Why This Works

• Single node eliminates distributed coordination

• In-memory operations are fast and atomic

• Version tracking enables optimistic concurrency

• Simple conflict detection and resolution

This foundation sets us up for multi-node distributed transactions - once we have solid single-node ACID, we can think about distributed ACID.

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