Good points.
web2py wraps each controller action in one transaction. The type of
transaction depends on the configuration of the database back-end.
If you use postgresql for example you can do:
db.executesql("SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;")
(optimistic locking)
and in you actions you can also do
while True:
try:
### perform you op
db.commit()
break
except OperationalError:
time.sleep(random.random()*1000) ### optional
db.rollback()
This should be equivalent to optimistic lock with retry.
There are many options. It depends on the database-backend. With
postgresql you have a lot of flexibility.
Massimo
On Oct 6, 12:48 am, billf <[EMAIL PROTECTED]> wrote:
> Hi - I am v.new to web2py (and python) and I am trying to find if
> there is any reason I should not try it as an alternative to Java
> servlets. I think I appreciate the savings I could make but I don't
> want to invest a lot of time and then find an unacceptable
> constraint. My apps are commercial, need to be robust but are not
> high volume enough for things like load balancing, etc.
>
> My concern at the moment is how to prevent updates being lost if 2
> users are simultaneously updating the same row. This may seem
> unlikely but I have always included a version number or
> last_action_timestamp in every table to allow update table set....
> where id=my_record.id and version=my_record.version.
>
> In my jargon this is "optimistic locking".
>
> How should I implement this in web2py?
>
> web2py always includes an id column (which is what I would do).
> Depending on the answer to the above question, would it be a good idea
> to also include a version number or last action timestamp and
> automatically check that.
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