[ZODB-Dev] newbie ZEO first try. ConflictError.

[Christian Theune]

Hi,

On 11/26/2009 10:55 PM, tsmiller wrote:
>
> Christian,
> Thanks. How painfully obvious.  I have written the words
> 'transaction.begin()' about a thousand times or so!  But I get
> discombobulated when I start looking at something new ( ZEO ) and forget the
> obvious.  Final code for this little test that works perfectly:
>
> while True:
>          transaction.begin()
>          root[ "one" ] = "program 2 - " + time.asctime()
>          while True:
>                  try:
>                          transaction.commit()
>                  except POSException.ConflictError:
>                          time.sleep(.2)
>                  else:
>                          break
>
>          time.sleep(5)

Two notes:

First, I'd leave the transaction.abort() right before the time.sleep(). 
Just to be explicit.

Second, the second while loop is superfluous - it doesn't do what it 
looks like and what you might think it does. ;)

You can try committing exactly once. If you commit after a conflict 
error, that will give you a different exception.

On the framework level conflict errors are usually handled by re-trying 
the *whole* transaction once more. E.g. in Zope it means:

- abort the transaction
- start a new transaction
- process the request as it was again

If it fails for three times then Zope gives up and hands the conflict 
error to the user.

Christian

-- 
Christian Theune · ct at gocept.com
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