dcgh...@gmail.com wrote:
> Hello there, > > I have the following code structure (more or less) in several processes: > > from sqlalchemy import create_engine > from sqlalchemy.orm import sessionmaker > > engine = create_engine(some_mysql_dburi) > session = sessionmaker(bind=engine)() > > while True: > query = session.query(...).filter(...) > # do something here from that query, update, insert new rows, etc. > session.commit() > > I am getting a too many connections error and it's not all the time, so I'm > not sure what would it be. Although there are several processes running, I > don't think at some time I'm connected to mysql server more than the amount > of connections allowed, which by default it's about 150 connections I think, > and I'm not modifying the default value. So I must have some errors in this > layout of my code. Here are some of the questions about the session and the > connection(s) within I'd like to ask: > 1- How many opened connections are maintained by a single session object? I > read somewhere it's only one, but, here it's my next if only one engine is associated with it, them just one connection. > 2- Does the session close the connection being used or requests for another? assuming the session isn’t in “autocommit” mode, the connection stays open until you call commit(), rollback(), or close(). > If it requests for a new one, does it close the previous (i.e., return it to > the engine pool)? just one connection at a time yup > 3- Should I call session.close() right after the session.commit() statement? it’s not necessary, however all objects that are associated with that session are still able to make it start up a new transaction if you keep using those objects and hit upon unloaded attributes. close() would prevent that. > If have to, do I have to put the session creation inside the while? not the way it is above; after that commit(), the Session there isn’t connected to anything. Unless the objects associated with it are being used in other threads, or something like that. > I read that when the session gets garbage collected the connection(s) is(are) > closed, that happens also but the commit() is enough (and close() makes it sure). > so I could do this, but I don't know if it is a good use of the session. > > I read the docs many times and I didn't find anything solid that answers that > questions to me, any help on the subject will be very appreciated, thanks in > advance. the best section is this one: http://docs.sqlalchemy.org/en/rel_0_9/orm/session_basics.html#when-do-i-construct-a-session-when-do-i-commit-it-and-when-do-i-close-it. > -- > 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/d/optout. -- 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/d/optout.
