Module wal 

Write-Ahead Log (WAL)

Provides durability guarantees for record operations.

Architecture

┌─────────────────────────────────────────────────────────────┐
│                   Write-Ahead Log (WAL)                      │
├─────────────────────────────────────────────────────────────┤
│  1. Log entry to WAL (fsync)                                 │
│  2. Apply to in-memory buffer                                │
│  3. Periodically checkpoint to persistent store              │
│  4. Truncate WAL after successful checkpoint                 │
└─────────────────────────────────────────────────────────────┘

Invariants

• INV-003: WAL-before-buffer (operations logged before applied)

Entry Types

• Insert: Add a new record
• UpdateStats: Update outcome statistics
• Delete: Mark record as deleted

Structs

WalConfig

WAL configuration.

WalEntry

A single WAL entry.

WalReader

WAL file reader.

WalWriter

Write-ahead log writer.

Enums

WalEntryType

Type of WAL entry.