issue_comments

Updated docs: https://docs.datasette.io/en/latest/getting_started.html#using-datasette-on-your-own-computer and https://docs.datasette.io/en/latest/cli-reference.html#datasette-serve-help

One thing to note is that the datasette-copy-to-memory plugin broke with a locked file, because it does this: https://github.com/simonw/datasette-copy-to-memory/blob/d541c18a78ae6f707a8f9b1e7fc4c020a9f68f2e/datasette_copy_to_memory/init.py#L27 python tmp.execute("ATTACH DATABASE ? AS _copy_from", [db.path]) That would need to use a URI filename too for it to work with locked files.

I'm going to skip adding a test for this - the test logic would have to be pretty convoluted to exercise it properly, and it's a pretty minor and low-risk feature in the scheme of things.

I tried writing a test like this:

python @pytest.mark.parametrize("locked", (True, False)) def test_locked_sqlite_db(tmp_path_factory, locked): dir = tmp_path_factory.mktemp("test_locked_sqlite_db") test_db = str(dir / "test.db") sqlite3.connect(test_db).execute("create table t (id integer primary key)") if locked: fp = open(test_db, "w") fcntl.lockf(fp.fileno(), fcntl.LOCK_EX) runner = CliRunner() result = runner.invoke( cli, [ "serve", "--memory", "--get", "/test", ], catch_exceptions=False, ) But it didn't work, because the test runs in the same process - so taking an exclusive lock on that file didn't cause an error when the test later tried to access it via Datasette!

I think I do that with fcntl.flock(): https://docs.python.org/3/library/fcntl.html#fcntl.flock

Not sure how to test this - I'd need to open my own lock against a database file somehow.

I knocked out a quick prototype of this and it worked!

datasette ~/Library/Application\ Support/Google/Chrome/Default/History --nolock

Here's the prototype diff:

```diff diff --git a/datasette/app.py b/datasette/app.py index b7b8437..f43700d 100644 --- a/datasette/app.py +++ b/datasette/app.py @@ -213,6 +213,7 @@ class Datasette: config_dir=None, pdb=False, crossdb=False, + nolock=False, ): assert config_dir is None or isinstance( config_dir, Path @@ -238,6 +239,7 @@ class Datasette: self.databases = collections.OrderedDict() self._refresh_schemas_lock = asyncio.Lock() self.crossdb = crossdb + self.nolock = nolock if memory or crossdb or not self.files: self.add_database(Database(self, is_memory=True), name="_memory") # memory_name is a random string so that each Datasette instance gets its own diff --git a/datasette/cli.py b/datasette/cli.py index 3c6e1b2..7e44665 100644 --- a/datasette/cli.py +++ b/datasette/cli.py @@ -452,6 +452,11 @@ def uninstall(packages, yes): is_flag=True, help="Enable cross-database joins using the /_memory database", ) +@click.option( + "--nolock", + is_flag=True, + help="Ignore locking and open locked files in read-only mode", +) @click.option( "--ssl-keyfile", help="SSL key file", @@ -486,6 +491,7 @@ def serve( open_browser, create, crossdb, + nolock, ssl_keyfile, ssl_certfile, return_instance=False, @@ -545,6 +551,7 @@ def serve( version_note=version_note, pdb=pdb, crossdb=crossdb, + nolock=nolock, )

 # if files is a single directory, use that as config_dir=

diff --git a/datasette/database.py b/datasette/database.py index 44d3266..fa55804 100644 --- a/datasette/database.py +++ b/datasette/database.py @@ -89,6 +89,8 @@ class Database: # mode=ro or immutable=1? if self.is_mutable: qs = "?mode=ro" + if self.ds.nolock: + qs += "&nolock=1" else: qs = "?immutable=1" assert not (write and not self.is_mutable) ```