"""SQLite in write-ahead-log mode (docs/database.md): readers no longer wait for a writer.

In the old rollback-journal mode a long write (the podcast refresh every 15 minutes, a book of
30 MB going in) kept every reader out until it was done, and requests failed with "database is
locked" — even GET /books/. WAL is set once per database file and stays; synchronous=NORMAL is
the safe pairing for it. A connection that can't switch (another one holds the file) just goes
on as it is; the next one switches.
"""
from django.db.backends.signals import connection_created


def _sqlite_wal(sender, connection, **kwargs):
    if connection.vendor != 'sqlite':
        return
    with connection.cursor() as cursor:
        try:
            cursor.execute('PRAGMA journal_mode=WAL')
        except Exception:  # noqa: BLE001 - locked right now; another connection will do it
            pass
        cursor.execute('PRAGMA synchronous=NORMAL')


connection_created.connect(_sqlite_wal, dispatch_uid='diora_sqlite_wal')