On May 31, 2010, at 3:43 AM, David wrote: > Hello, > > We are having a problem that is driving us crazy. We are in a load- > balanced environment, with 2 webservers using Django+SQLAlchemy, and > one database server. > > When a user is using the application, reads and writes work fine so > long as the user is on a single webserver. However, when we have a > load balancer with multiple web servers, sometimes the user is served > "cached" old, inaccurate data. > > Every time a page is accessed, the session is established as follows: > > engine = sqlalchemy.create_engine(ALCHEMY_DATABASE) > Session = sqlalchemy.orm.sessionmaker(bind=engine) > session = Session() > session.expire_all() > > We have tried all kinds of different configurations for "Session", but > everything seems to be giving us bad "cached" data. > > Can anybody please help? Thanks in advance. > > -David > > Example Scenario > 1.webA read from db ( colmun-data = 10 ) > 2.webA write to db ( colmun-data = 15 ) > OK > > 3.webB read from db ( colmun-data = 15 ) > 4.webB write to db ( colmun-data = 20 )increment 5 > STILL OK > > 5.webA read from db ( colmun-data = 10 ) > NOT OK - webA reads bad data
Since I don't see a rollback(), commit(), or close() (or autocommit=True) up there, you are probably seeing transaction isolation in effect. Once you select rows in your Session, MySQL establishes those rows as part of the current transaction. You'll get the same value back for them every time until you start a new transaction. http://dev.mysql.com/doc/refman/5.1/en/innodb-transaction-model.html > > > Environment: > two Django+SQLAlchemy Servers and one DatabaseServer > > Web Servers: > - Python2.6 > - Django1.1.1 > - SQLAlchemy 0.6 > - Mysql-python 1.2.3 > with Nginx + Djanogo runfcgi mode (min 10 max100 prefork) > on CentOS 5.4 running 2 phisical servers via ipvs loadbalancer > > Database Server: > - MySQLCluster 7.1 > on CentOS5.4 > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to sqlalch...@googlegroups.com. > To unsubscribe from this group, send email to > sqlalchemy+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sqlalchemy?hl=en. > -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
