sqlite3/README.md

# Go bindings to SQLite using Wazero

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Go module `github.com/ncruces/go-sqlite3` wraps a [WASM](https://webassembly.org/) build of [SQLite](https://sqlite.org/),
and uses [wazero](https://wazero.io/) to provide `cgo`-free SQLite bindings.

- Package [`github.com/ncruces/go-sqlite3`](https://pkg.go.dev/github.com/ncruces/go-sqlite3)
wraps the [C SQLite API](https://www.sqlite.org/cintro.html)
([example usage](https://pkg.go.dev/github.com/ncruces/go-sqlite3#example-package)).
- Package [`github.com/ncruces/go-sqlite3/driver`](https://pkg.go.dev/github.com/ncruces/go-sqlite3/driver)
provides a [`database/sql`](https://pkg.go.dev/database/sql) driver
([example usage](https://pkg.go.dev/github.com/ncruces/go-sqlite3/driver#example-package)).
- Package [`github.com/ncruces/go-sqlite3/embed`](https://pkg.go.dev/github.com/ncruces/go-sqlite3/embed)
embeds a build of SQLite into your application.
- Package [`github.com/ncruces/go-sqlite3/sqlite3vfs`](https://pkg.go.dev/github.com/ncruces/go-sqlite3/sqlite3vfs)
wraps the [C SQLite VFS API](https://www.sqlite.org/vfs.html) and provides a pure Go implementation.

### Caveats

This module replaces the SQLite [OS Interface](https://www.sqlite.org/vfs.html) (aka VFS)
with a [pure Go](sqlite3vfs/) implementation.
This has numerous benefits, but also comes with some drawbacks.

#### Write-Ahead Logging

Because WASM does not support shared memory,
[WAL](https://www.sqlite.org/wal.html) support is [limited](https://www.sqlite.org/wal.html#noshm).

To work around this limitation, SQLite is compiled with
[`SQLITE_DEFAULT_LOCKING_MODE=1`](https://www.sqlite.org/compile.html#default_locking_mode),
making `EXCLUSIVE` the default locking mode.
For non-WAL databases, `NORMAL` locking mode can be activated with
[`PRAGMA locking_mode=NORMAL`](https://www.sqlite.org/pragma.html#pragma_locking_mode).

Because connection pooling is incompatible with `EXCLUSIVE` locking mode,
the `database/sql` driver defaults to `NORMAL` locking mode.
To open WAL databases, or use `EXCLUSIVE` locking mode,
disable connection pooling by calling
[`db.SetMaxOpenConns(1)`](https://pkg.go.dev/database/sql#DB.SetMaxOpenConns).

#### POSIX Advisory Locks

POSIX advisory locks, which SQLite uses, are
[broken by design](https://www.sqlite.org/src/artifact/90c4fa?ln=1073-1161).

On Linux, macOS and illumos, this module uses
[OFD locks](https://www.gnu.org/software/libc/manual/html_node/Open-File-Description-Locks.html)
to synchronize access to database files.
OFD locks are fully compatible with process-associated POSIX advisory locks.

On BSD Unixes, this module uses
[BSD locks](https://man.freebsd.org/cgi/man.cgi?query=flock&sektion=2).
BSD locks may _not_ be compatible with process-associated POSIX advisory locks.

#### Testing

The pure Go VFS is stress tested by running an unmodified build of SQLite's
[mptest](https://github.com/sqlite/sqlite/blob/master/mptest/mptest.c)
on Linux, macOS and Windows.
Performance is tested by running
[speedtest1](https://github.com/sqlite/sqlite/blob/master/test/speedtest1.c).

### Roadmap

- [ ] advanced SQLite features
  - [x] nested transactions
  - [x] incremental BLOB I/O
  - [x] online backup
  - [ ] session extension
- [ ] custom SQL functions
- [ ] custom VFSes
  - [x] custom VFS API
  - [x] in-memory VFS
  - [x] read-only VFS, wrapping an [`io.ReaderAt`](https://pkg.go.dev/io#ReaderAt)
  - [ ] cloud-based VFS, based on [Cloud Backed SQLite](https://sqlite.org/cloudsqlite/doc/trunk/www/index.wiki)

### Alternatives

- [`modernc.org/sqlite`](https://pkg.go.dev/modernc.org/sqlite)
- [`crawshaw.io/sqlite`](https://pkg.go.dev/crawshaw.io/sqlite)
- [`github.com/mattn/go-sqlite3`](https://pkg.go.dev/github.com/mattn/go-sqlite3)
- [`github.com/zombiezen/go-sqlite`](https://pkg.go.dev/github.com/zombiezen/go-sqlite)