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Dot file locking. (#179)

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Nuno Cruces
2024-10-30 12:20:21 +00:00
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parent 1ad1608228
commit b2e8636227
14 changed files with 178 additions and 25 deletions
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19
vfs/README.md
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@@ -19,20 +19,19 @@ POSIX advisory locks, which SQLite uses on Unix, are
On Linux and macOS, this package 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 POSIX advisory locks.
This package can also use
[BSD locks](https://man.freebsd.org/cgi/man.cgi?query=flock&sektion=2),
albeit with reduced concurrency (`BEGIN IMMEDIATE` behaves like `BEGIN EXCLUSIVE`).
On BSD, macOS, and illumos, BSD locks are fully compatible with POSIX advisory locks;
on Linux and z/OS, they are fully functional, but incompatible;
elsewhere, they are very likely broken.
BSD locks are the default on BSD and illumos,
but you can opt into them with the `sqlite3_flock` build tag.
On Windows, this package uses `LockFileEx` and `UnlockFileEx`,
like SQLite.
You can also opt into a cross platform locking implementation
with the `sqlite3_dotlk` build tag.
Otherwise, file locking is not supported, and you must use
[`nolock=1`](https://sqlite.org/uri.html#urinolock)
(or [`immutable=1`](https://sqlite.org/uri.html#uriimmutable))
@@ -86,8 +85,8 @@ The implementation is compatible with SQLite's
### Build Tags
The VFS can be customized with a few build tags:
- `sqlite3_flock` forces the use of BSD locks; it can be used on z/OS to enable locking,
and elsewhere to test BSD locks.
- `sqlite3_flock` forces the use of BSD locks.
- `sqlite3_dotlk` forces the use of dot-file locks.
- `sqlite3_nosys` prevents importing [`x/sys`](https://pkg.go.dev/golang.org/x/sys);
disables locking _and_ shared memory on all platforms.
- `sqlite3_noshm` disables shared memory on all platforms.
@@ -96,17 +95,19 @@ The VFS can be customized with a few build tags:
> The default configuration of this package is compatible with the standard
> [Unix and Windows SQLite VFSes](https://sqlite.org/vfs.html#multiple_vfses);
> `sqlite3_flock` builds are compatible with the
> [`unix-flock` VFS](https://sqlite.org/compile.html#enable_locking_style).
> [`unix-flock` VFS](https://sqlite.org/compile.html#enable_locking_style);
> `sqlite3_dotlk` builds are compatible with the
> [`unix-dotfile` VFS](https://sqlite.org/compile.html#enable_locking_style).
> If incompatible file locking is used, accessing databases concurrently with
> _other_ SQLite libraries will eventually corrupt data.
### Custom VFSes
- [`github.com/ncruces/go-sqlite3/vfs/adiantum`](https://pkg.go.dev/github.com/ncruces/go-sqlite3/vfs/adiantum)
wraps a VFS to offer encryption at rest.
- [`github.com/ncruces/go-sqlite3/vfs/memdb`](https://pkg.go.dev/github.com/ncruces/go-sqlite3/vfs/memdb)
implements an in-memory VFS.
- [`github.com/ncruces/go-sqlite3/vfs/readervfs`](https://pkg.go.dev/github.com/ncruces/go-sqlite3/vfs/readervfs)
implements a VFS for immutable databases.
- [`github.com/ncruces/go-sqlite3/vfs/adiantum`](https://pkg.go.dev/github.com/ncruces/go-sqlite3/vfs/adiantum)
wraps a VFS to offer encryption at rest.
- [`github.com/ncruces/go-sqlite3/vfs/xts`](https://pkg.go.dev/github.com/ncruces/go-sqlite3/vfs/xts)
wraps a VFS to offer encryption at rest.