Write-Ahead Logging - SQLite

The persistence of WAL mode means that applications can be converted to using SQLite in WAL mode without making any changes to the application itself. One has merely to run " PRAGMA journal_mode=WAL; " on the database file (s) using the command-line shell or other utility, then restart the application.

SQLite WAL: Write-Ahead Logging Explained - SQL Docs

What is SQLite Write-Ahead Logging (WAL)? SQLite WAL is a crash-recovery mechanism that provides atomicity and durability guarantees for SQLite databases. Here's how it works: In WAL mode, all changes are first written to a separate WAL (write-ahead log) file. This happens before the changes are written to the actual database file.

Runnable SQLite Docs: WAL & Concurrency | Coddy

A practical guide to SQLite WAL mode: enabling write-ahead logging, how concurrent reads and writes work, checkpoints, the -wal and -shm files, and when not to use it.

SQLite Write-Ahead Logging (WAL) Explained in 3 Minutes

SQLite is a widely used database engine favored for its simplicity, low footprint, and being lightweight. In contrast to the traditional rollback journal mode of writing data, SQLite offers an alternative mechanism called Write-Ahead Logging (WAL). This technique can enhance concurrency and potentially improve the performance of database operations in many scenarios.

SQLite WAL mode: what changes and when to use it

SQLite WAL mode: what changes and when to use it Write-Ahead Logging explained for SQLite developers: concurrency, checkpointing, backup implications, and pragma settings.

Write-Ahead Logging (WAL) | sqlite/sqlite | DeepWiki

Purpose and Scope This page documents the WAL (Write-Ahead Logging) subsystem in SQLite, covering the on-disk WAL file format, the shared-memory WAL index (the -shm file), read and write transaction protocols, checkpoint operations, and the locking scheme used to coordinate concurrent access. WAL mode is one of two journaling modes in SQLite.

SQLite WAL Internals — Frame Format, wal-index, Checkpoints, and ...

SQLite Write-Ahead Logging WAL is the protocol that makes a SQLite database with multiple concurrent readers and a single writer behave like a real concurrent database. Set PRAGMA journal_mode=WAL once and reads stop blocking writes; writes stop blocking reads. The mechanism is a separate append-only log file, a tiny shared-memory index, and a checkpoint process that periodically folds the log ...

SQLite WAL Internals: Frames, Commits, Concurrency

A WAL frame is the fundamental unit of change in WAL mode. What a Frame Contains Each frame includes: Database page number Updated page content Frame header metadata Transaction reference How Frames Are Written When a transaction modifies data: SQLite identifies affected pages Each modified page is written as a frame into the WAL file Example ...

Write-Ahead Logging | SQLite Documentation

The persistence of WAL mode means that applications can be converted to using SQLite in WAL mode without making any changes to the application itself. One has merely to run " PRAGMA journal_mode=WAL; " on the database file (s) using the command-line shell or other utility, then restart the application.

SQLite WAL Mode Explained: Concurrent Reads and Writes (2026)

The primary problem WAL solves is the reader-writer conflict inherent in SQLite's default rollback journal modes. In rollback mode, writers lock the entire database, preventing any readers from accessing it. If a read operation is in progress when a write begins, the writer has to wait for the reader to finish.