Transaction Correctness Guide

Turso uses WAL (Write-Ahead Logging) mode exclusively.

Files: .db, .db-wal (no .db-shm - Turso uses in-memory WAL index)

WAL Mechanics

Write Path

1. Writer appends frames (page data) to WAL file (sequential I/O)
2. COMMIT = frame with non-zero db_size in header (marks transaction end)
3. Original DB unchanged until checkpoint

Read Path

1. Reader acquires read mark (mxFrame = last valid commit frame)
2. For each page: check WAL up to mxFrame, fall back to main DB
3. Reader sees consistent snapshot at its read mark

Checkpointing

Transfers WAL content back to main DB.