[Zope] ConflictError (ID-Counter for all Documents)

[Thomas Guettler]

     Toby Dickenson wrote:

>On Thu, 24 Jan 2002 11:59:18 +0100, Thomas Guettler
><zopestoller@thomas-guettler.de> wrote:
>
>>Catch the Exception, and retry it.
>>
>
>Dont catch it yourself. Zope is already doing this, and only shows the
>client an error message if it still fails after 3 attempts.
>
>>Use PCounter from ZODB/test/ConflictResolution.py
>>
>
>No, for two reasons:
>
>That class makes a good counter, but it is no use if you want to use
>the counter to generate unique ids. It works by allowing two
>transactions to proceed simultaneously with the same count value, then
>incrementing the count by two instead of one.
>
>Secondly, it wouldnt help even if it did generate unique ids. You
>would still get a conflict from the folder object.
>
>The easiest solution is to use only one publisher thread. That means
>no concurrency, no conflicts, but limited scalability.
>
Would this mean that if someone is downloading a 100MB file all other 
request have to wait?

I already asked this in an other thread: How can I get somethink like a 
syncronized block in Java?

syncronize{
 last_id=last_id+1
}

>
>You best solution is:
>
>1. Use a BTreeFolder (download it from www.zope.org), which allows for
>concurrent writes. It wont eliminate the need for retries, but it
>should decrease the probability of a failure after the three retries
>to an acceptable level.
>
I downloaded it. But it doesn't allow me to _setObject() of an int or a 
string.


>
>2. Use a different method of generating ids, to avoid the problem
>where two concurrent writes always generate the same id. The easiest
>solution is random ids.
>

I now use BTreeFolder to store all documents. The ID of  the documents 
is created with DateTime().millis()
This works much better than before, but still gives me some conflicts 
when I add the new document to the folder:

Sometimes I get a strange error:
2002-01-24T17:14:44 ERROR(200) ZODB Couldn't load state for 
'\x00\x00\x00\x00\x0
0\x00!\x0b'
Traceback (innermost last):
  File F:\ZOPE-2~1\lib\python\ZODB\Connection.py, line 446, in setstate
AttributeError: 'None' object has no attribute 'load'