Capstone: Mini Storage Engine

Why this module exists

Real systems are about composition. This capstone stitches together the core components you built: pages, WAL, recovery, and indexing. The result is a tiny but correct storage engine.

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1) Components

Your capstone includes:

• Slotted pages for records
• WAL for durability
• Recovery (redo + undo)
• B+Tree index for key lookups

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2) Failure model

We assume a crash can happen at any moment:

• pages may be dirty in memory
• WAL is durable up to its end

Recovery must produce a consistent state as if only committed transactions occurred.

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3) Correctness over speed

This is a toy engine. The goal is correctness and invariants, not throughput. The code should be small but explicit: every update must be logged and ordered.

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What you will build

• A mini key/value engine with WAL-backed recovery and indexed lookups.

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Key takeaways

• End-to-end correctness is a composition of small invariants.
• WAL and recovery are the backbone of durability.
• Index correctness depends on stable record IDs.