Tools for enabling and disabling WAL, closes #132

docs/cli.rst

@@ -684,13 +684,17 @@ To remove the FTS tables and triggers you created, use ``disable-fts``::
 
     $ sqlite-utils disable-fts mydb.db documents
 
+.. _cli_vacuum:
+
 Vacuum
 ======
 
 You can run VACUUM to optimize your database like so::
 
     $ sqlite-utils vacuum mydb.db
 
+.. _cli_optimize:
+
 Optimize
 ========
 
@@ -705,3 +709,18 @@ If you just want to run OPTIMIZE without the VACUUM, use the ``--no-vacuum`` fla
 
     # Optimize but skip the VACUUM
     $ sqlite-utils optimize --no-vacuum mydb.db
+
+.. _cli_wal:
+
+WAL mode
+========
+
+You can enable `Write-Ahead Logging <https://www.sqlite.org/wal.html>`__ for a database file using the ``enable-wal`` command::
+
+    $ sqlite-utils enable-wal mydb.db
+
+You can disable WAL mode using ``disable-wal``::
+
+    $ sqlite-utils disable-wal mydb.db
+
+Both of these commands accept one or more database files as arguments.

docs/python-api.rst

@@ -1195,6 +1195,8 @@ You can create a unique index by passing ``unique=True``:
 
 Use ``if_not_exists=True`` to do nothing if an index with that name already exists.
 
+.. _python_api_vacuum:
+
 Vacuum
 ======
 
@@ -1204,6 +1206,31 @@ You can optimize your database by running VACUUM against it like so:
 
     Database("my_database.db").vacuum()
 
+.. _python_api_wal:
+
+WAL mode
+========
+
+You can enable `Write-Ahead Logging <https://www.sqlite.org/wal.html>`__ for a database with ``.enable_wal()``:
+
+.. code-block:: python
+
+    Database("my_database.db").enable_wal()
+
+You can disable WAL mode using ``.disable_wal()``:
+
+.. code-block:: python
+
+    Database("my_database.db").disable_wal()
+
+You can check the current journal mode for a database using the ``journal_mode`` property:
+
+.. code-block:: python
+
+    journal_mode = Database("my_database.db").journal_mode
+
+This will usually be ``wal`` or ``delete`` (meaning WAL is disabled), but can have other values - see the `PRAGMA journal_mode <https://www.sqlite.org/pragma.html#pragma_journal_mode>`__ documentation.
+
 .. _python_api_suggest_column_types:
 
 Suggesting column types

sqlite_utils/cli.py

@@ -377,6 +377,32 @@ def disable_fts(path, table):
     db[table].disable_fts()
 
 
+@cli.command(name="enable-wal")
+@click.argument(
+    "path",
+    nargs=-1,
+    type=click.Path(exists=True, file_okay=True, dir_okay=False, allow_dash=False),
+    required=True,
+)
+def enable_wal(path):
+    "Enable WAL for database files"
+    for path_ in path:
+        sqlite_utils.Database(path_).enable_wal()
+
+
+@cli.command(name="disable-wal")
+@click.argument(
+    "path",
+    nargs=-1,
+    type=click.Path(exists=True, file_okay=True, dir_okay=False, allow_dash=False),
+    required=True,
+)
+def disable_wal(path):
+    "Disable WAL for database files"
+    for path_ in path:
+        sqlite_utils.Database(path_).disable_wal()
+
+
 def insert_upsert_options(fn):
     for decorator in reversed(
         (

sqlite_utils/db.py

@@ -170,6 +170,18 @@ def triggers(self):
             ).fetchall()
         ]
 
+    @property
+    def journal_mode(self):
+        return self.conn.execute("PRAGMA journal_mode;").fetchone()[0]
+
+    def enable_wal(self):
+        if self.journal_mode != "wal":
+            self.conn.execute("PRAGMA journal_mode=wal;")
+
+    def disable_wal(self):
+        if self.journal_mode != "delete":
+            self.conn.execute("PRAGMA journal_mode=delete;")
+
     def execute_returning_dicts(self, sql, params=None):
         cursor = self.conn.execute(sql, params or tuple())
         keys = [d[0] for d in cursor.description]

tests/test_cli.py

@@ -1230,6 +1230,37 @@ def test_drop_view_error():
         assert 'Error: View "t2" does not exist' == result.output.strip()
 
 
+def test_enable_wal():
+    runner = CliRunner()
+    dbs = ["test.db", "test2.db"]
+    with runner.isolated_filesystem():
+        for dbname in dbs:
+            db = Database(dbname)
+            db["t"].create({"pk": int}, pk="pk")
+            assert db.journal_mode == "delete"
+        result = runner.invoke(cli.cli, ["enable-wal"] + dbs)
+        assert 0 == result.exit_code
+        for dbname in dbs:
+            db = Database(dbname)
+            assert db.journal_mode == "wal"
+
+
+def test_disable_wal():
+    runner = CliRunner()
+    dbs = ["test.db", "test2.db"]
+    with runner.isolated_filesystem():
+        for dbname in dbs:
+            db = Database(dbname)
+            db["t"].create({"pk": int}, pk="pk")
+            db.enable_wal()
+            assert db.journal_mode == "wal"
+        result = runner.invoke(cli.cli, ["disable-wal"] + dbs)
+        assert 0 == result.exit_code
+        for dbname in dbs:
+            db = Database(dbname)
+            assert db.journal_mode == "delete"
+
+
 @pytest.mark.parametrize(
     "args,expected",
     [