OperationalError: database is locked

Question

I have made some repetitive operations in my application (testing it), and suddenly I’m getting a weird error:

OperationalError: database is locked

I've restarted the server, but the error persists. What can it be all about?

Answer 1

From django doc:

SQLite is meant to be a lightweight database, and thus can't support a high level of concurrency. OperationalError: database is locked errors indicate that your application is experiencing more concurrency than sqlite can handle in default configuration. This error means that one thread or process has an exclusive lock on the database connection and another thread timed out waiting for the lock the be released.

Python's SQLite wrapper has a default timeout value that determines how long the second thread is allowed to wait on the lock before it times out and raises the OperationalError: database is locked error.

If you're getting this error, you can solve it by:

• Switching to another database backend. At a certain point SQLite becomes too "lite" for real-world applications, and these sorts of concurrency errors indicate you've reached that point.
• Rewriting your code to reduce concurrency and ensure that database transactions are short-lived.
• Increase the default timeout value by setting the timeout database option

http://docs.djangoproject.com/en/dev/ref/databases/#database-is-locked-errorsoption

Answer 2

In my case, It was because I open the database from SQLite Browser. When I close it from the browser, the problem is gone.

Answer 3

The practical reason for this is often that the python or django shells have opened a request to the DB and it wasn't closed properly; killing your terminal access often frees it up. I had this error on running command line tests today.

Edit: I get periodic upvotes on this. If you'd like to kill access without rebooting the terminal, then from commandline you can do:

from django import db
db.connections.close_all()

Answer 4

I disagree with @Patrick's answer which, by quoting this doc, implicitly links OP's problem (Database is locked) to this:

Switching to another database backend. At a certain point SQLite becomes too "lite" for real-world applications, and these sorts of concurrency errors indicate you've reached that point.

This is a bit "too easy" to incriminate SQlite for this problem (which is very powerful when correctly used; it's not only a toy for small databases, fun fact: An SQLite database is limited in size to 140 terabytes).

Unless you have a very busy server with thousands of connections at the same second, the reason for this Database is locked error is probably more a bad use of the API, than a problem inherent to SQlite which would be "too light". Here are more informations about Implementation Limits for SQLite.

---

Now the solution:

I had the same problem when I was using two scripts using the same database at the same time:

• one was accessing the DB with write operations
• the other was accessing the DB in read-only

Solution: always do cursor.close() as soon as possible after having done a (even read-only) query.

Here are more details.

Answer 5

As others have told, there is another process that is using the SQLite file and has not closed the connection. In case you are using Linux, you can see which processes are using the file (for example db.sqlite3) using the fuser command as follows:

$ sudo fuser -v db.sqlite3
                     USER        PID ACCESS COMMAND
/path/to/db.sqlite3:
                     user        955 F....  apache2

If you want to stop the processes to release the lock, use fuser -k which sends the KILL signal to all processes accessing the file:

sudo fuser -k db.sqlite3

Note that this is dangerous as it might stop the web server process in a production server.

Thanks to @cz-game for pointing out fuser!

Answer 6

I encountered this error message in a situation that is not (clearly) addressed by the help info linked in patrick's answer.

When I used transaction.atomic() to wrap a call to FooModel.objects.get_or_create() and called that code simultaneously from two different threads, only one thread would succeed, while the other would get the "database is locked" error. Changing the timeout database option had no effect on the behavior.

I think this is due to the fact that sqlite cannot handle multiple simultaneous writers, so the application must serialize writes on their own.

I solved the problem by using a threading.RLock object instead of transaction.atomic() when my Django app is running with a sqlite backend. That's not entirely equivalent, so you may need to do something else in your application.

Here's my code that runs FooModel.objects.get_or_create simultaneously from two different threads, in case it is helpful:

from concurrent.futures import ThreadPoolExecutor

import configurations
configurations.setup()

from django.db import transaction
from submissions.models import ExerciseCollectionSubmission

def makeSubmission(user_id):
    try:
        with transaction.atomic():
            e, _ = ExerciseCollectionSubmission.objects.get_or_create(
                student_id=user_id, exercise_collection_id=172)
    except Exception as e:
        return f'failed: {e}'

    e.delete()

    return 'success'


futures = []

with ThreadPoolExecutor(max_workers=2) as executor:
    futures.append(executor.submit(makeSubmission, 296))
    futures.append(executor.submit(makeSubmission, 297))

for future in futures:
    print(future.result())

Answer 7

This also could happen if you are connected to your sqlite db via dbbrowser plugin through pycharm. Disconnection will solve the problem

Answer 8

For me it gets resolved once I closed the django shell which was opened using python manage.py shell

Answer 9

I've got the same error! One of the reasons was the DB connection was not closed. Therefore, check for unclosed DB connections. Also, check if you have committed the DB before closing the connection.

Answer 10

I had a similar error, right after the first instantiation of Django (v3.0.3). All recommendations here did not work apart from:

• deleted the db.sqlite3 file and lose the data there, if any,
• python manage.py makemigrations
• python manage.py migrate

---

Btw, if you want to just test PostgreSQL:

docker run --rm --name django-postgres \
  -e POSTGRES_PASSWORD=mypassword \
  -e PGPORT=5432 \
  -e POSTGRES_DB=myproject \
  -p 5432:5432 \
  postgres:9.6.17-alpine

Change the settings.py to add this DATABASES:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': 'myproject',
        'USER': 'postgres',
        'PASSWORD': 'mypassword',
        'HOST': 'localhost',
        'PORT': '5432',
    }
}

...and add database adapter:

pip install psycopg2-binary

Then the usual:

python manage.py makemigrations
python manage.py migrate

Answer 11

Just close (stop) and open (start) the database. This solved my problem.

Answer 12

I found this worked for my needs. (thread locking) YMMV conn = sqlite3.connect(database, timeout=10)

https://docs.python.org/3/library/sqlite3.html

sqlite3.connect(database[, timeout, detect_types, isolation_level, check_same_thread, factory, cached_statements, uri])

When a database is accessed by multiple connections, and one of the processes modifies the database, the SQLite database is locked until that transaction is committed. The timeout parameter specifies how long the connection should wait for the lock to go away until raising an exception. The default for the timeout parameter is 5.0 (five seconds).

Answer 13

In my case, I added a new record manually saved and again through shell tried to add new record this time it works perfectly check it out.

In [7]: from main.models import Flight

In [8]: f = Flight(origin="Florida", destination="Alaska", duration=10)

In [9]: f.save()

In [10]: Flight.objects.all() 
Out[10]: <QuerySet [<Flight: Flight object (1)>, <Flight: Flight object (2)>, <Flight: Flight object (3)>, <Flight: Flight object (4)>]>

Answer 14

I got this error when using a database file saved under WSL (\\wsl$ ...) and running a windows python interpreter.

You can either not save the database in your WSL-tree or use a linux based interpreter in your distro.

Answer 15

In my case, I had not saved a database operation I performed within the SQLite Browser. Saving it solved the issue.

Answer 16

A very unusual scenario, which happened to me.

There was infinite recursion, which kept creating the objects.

More specifically, using DRF, I was overriding create method in a view, and I did

def create(self, request, *args, **kwargs):
    ....
    ....

    return self.create(request, *args, **kwargs)

Answer 17

Already lot of Answers are available here, even I want to share my case , this may help someone..

I have opened the connection in Python API to update values, I'll close connection only after receiving server response. Here what I did was I have opened connection to do some other operation in server as well before closing the connection in Python API.

Answer 18

If you get this error while using manage.py shell, one possible reason is that you have a development server running (manage.py runserver) which is locking the database. Stoping the server while using the shell has always fixed the problem for me.

Answer 19

actually I have faced same problem , when I use "transaction.atomic() with select_for_update() " i got error message "the OperationalError: database is locked" ,

and after many tries / searching / read django docs , i found the problem from SQLite itself it is not support select_for_update method as django DOCs says , kindly have a look at the following url and read it deeply:

https://docs.djangoproject.com/en/dev/ref/databases/#database-is-locked-errors

, and when i moved to MySQL everything goes fine .

as django DOCs also says "database is locked" may happen when database timeout occur , they recommend you to change database timeout by setting up the following option :

'OPTIONS': {
    # ...
    'timeout': 20,
    # ...
}

finally, I recommend you to use MySQL/PostgreSQL even if you working on development environment .

I hope this helpful for you .

Answer 20

I got this error when attempting to create a new table in SQLite but the session object contained uncommitted (though flushed) changes.

Make sure to either:

1. Commit the session(s) before creating a new table
2. Close all sessions and perform the table creation in a new connection
3. ...

Answer 21

UPDATE django version 2.1.7

I got this error sqlite3.OperationalError: database is locked using pytest with django.

Solution:

If we are using @pytest.mark.django_db decorator. What it does is create a in-memory-db for testing.

Named: file:memorydb_default?mode=memory&cache=shared We can get this name with:

from django.db import connection
db_path = connection.settings_dict['NAME']

To access this database and also edit it, do:

Connect to the data base:

with sqlite3.connect(db_path, uri=True) as conn:
    c = conn.cursor()

Use uri=True to specifies the disk file that is the SQLite database to be opened.

To avoid the error activate transactions in the decorator:

@pytest.mark.django_db(transaction=True)

Final function:

from django.db import connection

@pytest.mark.django_db(transaction=True)
def test_mytest():
    db_path = connection.settings_dict['NAME']
    with sqlite3.connect(db_path, uri=True) as conn:
        c = conn.cursor()
        c.execute('my amazing query')
        conn.commit()
    assert ... == ....

Answer 22

Just reboot your server, it will clear all current processes that have your database locked.

Answer 23

try this command:

sudo fuser -k 8000/tcp