Python SQLite: database is locked

问题:

I'm trying this code:

import sqlite

connection = sqlite.connect('cache.db')
cur = connection.cursor()
cur.execute('''create table item
  (id integer primary key, itemno text unique,
        scancode text, descr text, price real)''')

connection.commit()
cur.close()

I'm catching this exception:

Traceback (most recent call last):
  File "cache_storage.py", line 7, in <module>
    scancode text, descr text, price real)''')
  File "/usr/lib/python2.6/dist-packages/sqlite/main.py", line 237, in execute
    self.con._begin()
  File "/usr/lib/python2.6/dist-packages/sqlite/main.py", line 503, in _begin
    self.db.execute("BEGIN")
_sqlite.OperationalError: database is locked

Permissions for cache.db are ok. Any ideas?

回答1:

I'm presuming you are actually using sqlite3 even though your code says otherwise. Here are some things to check:

1. That you don't have a hung process sitting on the file (unix: $ fuser cache.db should say nothing)
2. There isn't a cache.db-journal file in the directory with cache.db; this would indicate a crashed session that hasn't been cleaned up properly.
3. Ask the database shell to check itself: $ sqlite3 cache.db "pragma integrity_check;"
4. Backup the database $ sqlite3 cache.db ".backup cache.db.bak"
5. Remove cache.db as you probably have nothing in it (if you are just learning) and try your code again
6. See if the backup works $ sqlite3 cache.db.bak ".schema"

Failing that, read Things That Can Go Wrong and How to Corrupt Your Database Files

回答2:

Set the timeout parameter in your connect call, as in:

connection = sqlite.connect('cache.db', timeout=10)

回答3:

I know this is old, but I'm still getting the problem and this is the first link on Google for it. OP said his issue was that the .db was sitting on a SMB share, which was exactly my situation. My ten minutes' research indicates that this is a known conflict between sqlite3 and smb; I've found bug reports going back to 2007.

I resolved it by adding the "nobrl" option to my smb mount line in /etc/fstab, so that line now looks like this:

//SERVER/share /mnt/point cifs credentials=/path/to/.creds,sec=ntlm,nobrl 0 0

This option prevents your SMB client from sending byte range locks to the server. I'm not too up on my SMB protocol details, but I best I can tell this setting would mostly be of concern in a multi-user environment, where somebody else might be trying to write to the same db as you. For a home setup, at least, I think it's safe enough.

My relevant versions:

• Mint 17.1 Rebecca
• SMB v4.1.6-Ubuntu
• Python v3.4.0
• SQLite v3.8.2
• Network share is hosted on a Win12R2 server

回答4:

Turned out the problem happened because the path to the db file was actually a samba mounted dir. I moved it and that started working.

回答5:

In Linux you can do something similar, for example, if your locked file is development.db:

$ fuser development.db This command will show what process is locking the file:

development.db: 5430 Just kill the process...

kill -9 5430 ...And your database will be unlocked.

回答6:

The reason mine was showing the "Lock" message was actually due to me having opened an SQLite3 IDE on my mac and that was the reason it was locked. I assume I was playing around with the DB within the IDE and hadn't saved the changes and therefor a lock was placed.

Cut long story short, check that there are no unsaved changes on the db and also that it is not being used elsewhere.

回答7:

The database is locked by another process that is writing to it. You have to wait until the other transaction is committed. See the documentation of connect()

回答8:

Here's a neat workaround for simultaneous access:

while True:
    connection = sqlite3.connect('user.db', timeout=1)
    cursor = connection.cursor()
    try:
        cursor.execute("SELECT * FROM queue;")
        result = cursor.fetchall()
    except sqlite3.OperationalError:
        print("database locked")
    num_users = len(result)
# ...

回答9:

Because this is still the top Google hit for this problem, let me add a possible cause. If you're editing your database structure and haven't committed the changes, the database is locked until you commit or revert.

(Probably uncommon, but I'm developing an app so the code and database are both being developed at the same time)

回答10:

You should check out if there is no DBMS administration and development platform working on your database (like pgAdmin), as this is probably the most popular cause of this error. If there is - commit the changes done and the problem is gone.

回答11:

One possible reason for the database being locked that I ran into with SQLite is when I tried to access a row that was being written by one app, and read by another at the same time. You may want to set a busy timeout in your SQLite wrapper that will spin and wait for the database to become free (in the original c++ api the function is sqlite3_busy_timeout). I found that 300ms was sufficient in most cases.

But I doubt this is the problem, based on your post. Try other recommendations first.

回答12:

1. Your cache.db is being currently used by another process.
2. Stop that process and try again, it should work.

回答13:

I had this problem while working with Pycharm and with a database that was originally given to me by another user.

So, this is how I solve it in my case:

1. Closed all tabs in Pycharm that operate with the problematic database.
2. Stop all running processes from the red square botton in the top right corner of Pycharm.
3. Delete the problematic database from the directory.
4. Upload again the original database. And it worked again.

回答14:

Oh, your traceback gave it away: you have a version conflict. You have installed some old version of sqlite in your local dist-packages directory when you already have sqlite3 included in your python2.6 distribution and don't need and probably can't use the old sqlite version. First try:

$ python -c "import sqlite3"

and if that doesn't give you an error, uninstall your dist-package:

easy_install -mxN sqlite

and then import sqlite3 in your code instead and have fun.

回答15:

I had the same problem: sqlite3.IntegrityError

As mentioned in many answers, the problem is that a connection has not been properly closed.

In my case I had try except blocks. I was accessing the database in the try block and when an exception was raised I wanted to do something else in the except block.

try:
    conn = sqlite3.connect(path)
    cur = conn.cursor()
    cur.execute('''INSERT INTO ...''')
except:
    conn = sqlite3.connect(path)
    cur = conn.cursor()
    cur.execute('''DELETE FROM ...''')
    cur.execute('''INSERT INTO ...''')

However, when the exception was being raised the connection from the try block had not been closed.

I solved it using with statements inside the blocks.

try:
    with sqlite3.connect(path) as conn:
        cur = conn.cursor()
        cur.execute('''INSERT INTO ...''')
except:
    with sqlite3.connect(path) as conn:
        cur = conn.cursor()
        cur.execute('''DELETE FROM ...''')
        cur.execute('''INSERT INTO ...''')

回答16:

I also had this problem. I was trying to enter data into the database without saving changes I had made in it. after i saved the changes worked