Sqlite database locked - regression introduced in 2.4.5?

Below an excerpt from my CherryPy app.

The app receives bursts of ajax calls to cncprogram_done. Sometimes just 1 or 2 calls, sometimes up to 10 or 20 at a time (I will eventually optimize it, but for now I’m OK with it).

I just upgraded to Peewee 2.8.3 and only the first call of each burst works, the other calls say peewee.OperationalError: database is locked while executing part.save().

I tried to revert to older versions, and I found out that with Peewee 2.4.4 works well and with the 2.4.5 fails.

I reverted back to 2.4.4 on the production server and everything seems to work fine.

Any idea whether I am doing something wrong or this is really a regression? Where do I start investigating?

Here is (part of) the code:

db = peewee.SqliteDatabase(path_name + '/doc.db', threadlocals=True)

class PeeweeModel(peewee.Model):
    class Meta:
        database = db

class CncProgramPart(PeeweeModel):
    sheet = peewee.ForeignKeyField(CncProgramSheet, related_name='parts')
    part_number = peewee.CharField()
    time_finished = peewee.DateTimeField(default=0)
    remake = peewee.BooleanField(default=False)
    comment = peewee.CharField(default='')

    def render(self, settings):
        return render('cncprogram_edit_part_row.html',
                      {'part': self, 'settings': settings})

class DocFinder:

    @cherrypy.expose
    def cncprogram_done(self, rowid, value):

        with db.transaction():
            checked = value == 'true'
            now = time.time()
            part = CncProgramPart.get(CncProgramPart.id == rowid[9:])

            if checked and not part.remake and not part.comment:
                part.time_finished = now
                part.comment = ''
                part.remake = False
                part.save()
            elif part.time_finished:
                part.time_finished = 0
                part.save()

            return part.render(Settings())

[coleifer]

Another thing you should always be doing is specifying journal_mode='wal' when you instantiate your Sqlite database. This allows multiple readers to co-exist with a single writer, and I think this may also magically solve your issues:

db = SqliteDatabase('foo.db', pragmas=[('journal_mode', 'wal')])

[coleifer]

I have something awesome you can try…

It’s currently only in master branch, but if you want to try it out it should solve your problem.

In the playhouse.sqliteq module is a class named SqliteQueueDatabase. Replace this:

db = peewee.SqliteDatabase('test.db')

With this:

from playhouse.sqliteq import SqliteQueueDatabase
db = SqliteQueueDatabase('t.db', readers=4, autostart=True)

At the same time, remove all calls to db.connect() and db.close().