well, that's why I asked about his FS config earlier today. I got some strange behaviors from sqlite using ssd drives with some specific set of options for the filesystem; but I'm also not using the latest version of sqlite ... 3.7.9 here, as of ubuntu 12.04 lts. I really didn't narrowed it down because I was using a dev machine, not production -- which is read only and doesn't have concurrency.
best regards, richard. Em 2014-01-20 19:33, Michael Bayer escreveu: > On Jan 20, 2014, at 3:59 PM, pr64 <pierrerot...@gmail.com [6]> wrote: > >> OK, sorry for my explanation which is not right. >> I launch two separate processes from the command line. Each is importing my API and therefore creates its own connection to the sqlite database. >> Commiting in process 1 should be visible from process 2. The problem I have is that the change is seen seconds later in process 2. No session is shared, each process having its own. What I can observe is that if I close session just after commiting in process 1, then process 2 sees the change as expected. If the session is not closed in process 1 (just commiting) then, the change is not seen in process 2... :-( > > this sounds like basic isolation behavior. If process 2 is still running in a transaction that was started before process 1 committed, then the database isolation behavior would determine what can be seen in process 2 within that transaction. > SQLite's concurrency behavior is not something I have a deep understanding of, as it is file-based and more simplistic than a modern MVCC-style database, it has some complicated locking and journaling behavior described at http://sqlite.org/lang_transaction.html [7]. The answer to your question is likely described within this documentation. > >> I've got a an OrmManager class: >> >> class OrmManager: def __init__(self, database, metadata, echo=False): self.database = database engine = create_engine('sqlite:///' + database, echo=echo, connect_args={'detect_types': sqlite3.PARSE_DECLTYPES| sqlite3.PARSE_COLNAMES}, native_datetime=True, poolclass=NullPool, convert_unicode=True ) metadata.create_all(engine) # this factory is thread safe: a session object is returned (always the same) to the # caller. If called from another thread, the returned session object will be different session_factory = sessionmaker(bind=engine, expire_on_commit=False) self.session = scoped_session(session_factory) def get_session(self): session = self.session() return session >> and in P1 and P2, I instantiate it: >> >> orm_mgr = OrmManager(database=<path/to/my/.sqlite/file>, metadata=METADATA) session = orm_mgr.get_session() # do some stuff here session.commit() >> >> On Monday, January 20, 2014 5:12:58 PM UTC+1, pr64 wrote: >> >>> Hi, >>> Strange behaviour with sqa in multi-process environment... already posted on StackOverflow [1] for a web app but still missing some understanding so posting here. >>> I've created an application where my "sqa calls" are encapsulated: My API's methods always do the same kind of stuff: >>> 1- request a session >>> 2- do my stuff - mainly requesting the db through session.query(...) >>> 3- eventually: >>> - modify some mapped object attributes >>> - and write to db (session.commit()). >>> Several consecutive calls to my API's methods return the same session object as long as I'm in the same thread which is the required behaviour. Some commits happen but the session is always the same (expire_on_commit = False) >>> # this factory is thread safe: a session object is returned (always the same) to the >>> # caller. If called from another thread, the returned session object will be different >>> session_factory = sessionmaker(bind=engine, expire_on_commit=False) >>> session_maker = scoped_session(session_factory) >>> # to get a session: >>> session = session_maker() >>> If I fork another thread, using the API is still safe since the first step (getting a session) will return a new session instance (due to scoped_session) >>> Here's my problem: >>> I have two processes which such an architecture (based on this API). While P1 is writing to DB (session.commit()), P2 is reading from it (session.query(...)). The problem is that P2 does not see the DB change and has to poll several times before getting it. I'm actually requesting the DB through session.query(...) calls from P2 but nothing happens. SOMETIMES IT WORKS THOUGH! :-( Don't know why (did not change the code) -> Over 10 times, it will work 3 times... >>> If I change my API to close the session after every commit, P2 sees the change as if commiting was not actually writing to disk and closing the session did it. I do not understand this behavour as the sqa documentation encourages to create a global session in a thread a work with it (which is done with the scoped_session mechanism) >>> My configuration is : Linux OS, SQA 0.8.4 and a ram based db (/dev/shm/my_db.sqlite but the problem is still there with regular disk based db on my ~/my_db.sqlite) >>> Thanks a lot for your time, >>> Pierre >> -- >> You received this message because you are subscribed to the Google Groups "sqlalchemy" group. >> To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com [2]. >> To post to this group, send email to sqlalchemy@googlegroups.com [3]. >> Visit this group at http://groups.google.com/group/sqlalchemy [4]. >> For more options, visit https://groups.google.com/groups/opt_out [5]. Links: ------ [1] http://stackoverflow.com/questions/21109794/delayed-change-using-sqlalchemy [2] mailto:sqlalchemy+unsubscr...@googlegroups.com [3] mailto:sqlalchemy@googlegroups.com [4] http://groups.google.com/group/sqlalchemy [5] https://groups.google.com/groups/opt_out [6] mailto:pierrerot...@gmail.com [7] http://sqlite.org/lang_transaction.html -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/groups/opt_out.
