OperationalError: database is locked

问题

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?

回答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 optionoption

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

回答2:

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()

回答3:

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

回答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.

回答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!

回答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())

回答7:

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

回答8:

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.

回答9:

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

回答10:

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

回答11:

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 ... == ....

回答12:

try this command:

sudo fuser -k 8000/tcp

来源：https://stackoverflow.com/questions/3172929/operationalerror-database-is-locked

标签

python

django

database

sqlite

locked