On Oct 22, 2008, at 9:47 PM, dave wrote:
> > Hi there, > > I am using SQLAlchemy in a multi-threaded app with a SQLite backend. > I've been careful to scope sessions down to a single method and made > sure a session is never used by more than one thread. > > Some threads are reading data from the DB, some are writing it, some > are updating it. As could have been expected, those commit() calls > committing updates or inserts sometimes error out with > "OperationalError: (OperationalError) database is locked" errors. > > I can only imagine another thread is in the middle of reading from or > writing to the DB and in possession of a shared or exclusive lock. > > It appears SQLAlchemy won't wait for the lock to become available nor > will it retry a failed operation - is that correct? usually, the transactional capabilities of the database handle contention of resources. SQLite is designed specifically to suck at this. retrying failed operations is also outside of the scope of SQLA since "failure" is an incredibly broad category for which recovery scenarios vary wildly, if even available. > Is there a > recommended pattern or method for handling multiple simultaneous reads > and writes? Given that some of the data from the DB is being lazy > loaded as instances are being used, how would I use mutexes to control > access to the DB (if that's even what I should be doing)? you could use mutexes, or alternatively lockfiles, since you're ultimately dealing with a file based resource. most people that start having contention issues with SQLite just switch to PG or MySQL. Here's some "multiple reader/single writer" synchronizers of each type (see FileSynchronizer, ConditionSynchronizer) used by Beaker to synchronize access to dbm and flat files: https://www.knowledgetap.com/hg/beaker/file/7621e71729b3/beaker/synchronization.py if you have success with those in this context, let me know. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~----------~----~----~----~------~----~------~--~---
