The problem sums up to: I expect when committing that something like 
"saving a file" happens...everybody, and I mean everybody trying to access 
that file later would read the same thing.
SQlite, MSSQL, Postgresql, Oracle adapters work this way, and I assume also 
mongo and couchdb.
I tried to read the PEP for the DBAPI and saw no explicit references to 
what committing should do in reference to a multiprocess environment (i.e. 
if commit should "save" the changes and make them available for other 
processes). 
However, I'm not a python guru to rule that out, I'm just saying that from 
a DAL point of view having to commit before reading to see records 
changed/inserted by other processes is required ONLY from mysql.

On Tuesday, August 14, 2012 6:15:14 AM UTC+2, Massimo Di Pierro wrote:
>
> Should we change the settings in the Adapter?
>
> On Monday, 13 August 2012 17:21:09 UTC-5, Niphlod wrote:
>>
>> The most probable cause is the transaction isolation "problem" with mysql 
>> as explained in 
>> https://groups.google.com/d/msg/web2py/qLHP3iYz8Lo/Ly2wqK4qZZgJ
>>
>> I'm starting to think that it's the only adapter behaving differently.
>>
>> On Monday, August 13, 2012 11:46:11 PM UTC+2, Florian Letsch wrote:
>>>
>>> Yes, I am using mysql.
>>>
>>> I've accidentally posted this twice [0] on the group (sorry for that). 
>>> Anthony asked:
>>> > How are emails added to the database -- does that happen within the 
>>> application, or also in a script?
>>>
>>> Emails are added to the database from within the application (a 
>>> controller function adds a confirmation email to the queue)
>>>
>>> [0] 
>>> https://groups.google.com/forum/?fromgroups#!topic/web2py/YT2jDMea6lU
>>>
>>> On Sunday, 12 August 2012 07:17:39 UTC+12, Massimo Di Pierro wrote:
>>>>
>>>> Are you using mysql?
>>>>
>>>> On Friday, 10 August 2012 23:11:03 UTC-5, Florian Letsch wrote:
>>>>>
>>>>> I want to send emails using a background queue as described in the 
>>>>> web2py book: 
>>>>> http://web2py.com/books/default/chapter/29/8#Sending-messages-using-a-background-task
>>>>>
>>>>> However, the queue only sends emails that have been in the database 
>>>>> when I start the script. Database entries added lateron don't get picked 
>>>>> up 
>>>>> by the script. The only way I can achieve that is to add another 
>>>>> db.commit() before the select(). I am sure this is not supposed to be 
>>>>> necessary. Does anyone know why this is happening?
>>>>>
>>>>> import time
>>>>> while True:
>>>>>     db.commit() # Only works if I add this line
>>>>>     rows = db(db.queue.status=='pending').select()
>>>>>     for row in rows:
>>>>>         if mail.send(to=row.email,
>>>>>             subject=row.subject,
>>>>>             message=row.message):
>>>>>             row.update_record(status='sent')
>>>>>         else:
>>>>>             row.update_record(status='failed')
>>>>>         db.commit()
>>>>>     time.sleep(60) # check every minute
>>>>>
>>>>>

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