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sqlite3/README.md
Nuno Cruces 738714bf32 Fix WAL.
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# Go bindings to SQLite using Wazero
[![Go Reference](https://pkg.go.dev/badge/image)](https://pkg.go.dev/github.com/ncruces/go-sqlite3)
[![Go Report](https://goreportcard.com/badge/github.com/ncruces/go-sqlite3)](https://goreportcard.com/report/github.com/ncruces/go-sqlite3)
[![Go Coverage](https://github.com/ncruces/go-sqlite3/wiki/coverage.svg)](https://github.com/ncruces/go-sqlite3/wiki/Test-coverage-report)
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/vfs`](https://pkg.go.dev/github.com/ncruces/go-sqlite3/vfs)
wraps the [C SQLite VFS API](https://www.sqlite.org/vfs.html) and provides a pure Go implementation.
- Package [`github.com/ncruces/go-sqlite3/gormlite`](https://pkg.go.dev/github.com/ncruces/go-sqlite3/gormlite)
provides a [GORM](https://gorm.io) driver.
### Caveats
This module replaces the SQLite [OS Interface](https://www.sqlite.org/vfs.html)
(aka VFS) with a [pure Go](vfs/) implementation.
This has 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 [patched](sqlite3/locking_mode.patch)
to always use `EXCLUSIVE` locking mode for WAL databases.
Because connection pooling is incompatible with `EXCLUSIVE` locking mode,
to open WAL databases you should 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 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 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)
- [ ] custom SQL functions
### 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)