Hey,
I'm using sqlalchemy-0.4.8 with mysql-5.0 on innodb tables. I'm having
trouble updating 1 field in 1 row concurrently. The problem is that I
can't seem to reliably update the fields. Simple example:
Program 1:
..
session.close()
session.begin()
u = User.get(id=1).with_lockmode("update").first()
print(u.bytes)
u.bytes += 100
time.sleep(5)
session.commit()
Program 2:
..
session.close()
session.begin()
u = User.get(id=1).with_lockmode("update").first()
print(u.bytes)
u.bytes -= 10
session.commit()
print(u.trafficbytes)
I start by running program 1 until it enters the sleep. It's holding
the update lock on the user table. Now, I run program 2. It nicely
waits until program 1 commits the session. However, u.bytes still has
the value _before_ program 1 adds 100 to it. I expected it to get the
newly, updated value.
What am I doing wrong here? Is it because program 2 gets the database
state it was in at the moment it starts the database transaction with
session.begin() (while program 1 hasn't committed its update yet)? If
so, how do I rewrite the code to get it to do what I mean?
Kind regards,
Bram
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