[Zope-DB] newbie: read access to a object in midst of transaction

Nesbitt, Steve snesbitt at cobaltgroup.com
Tue Oct 7 19:27:23 EDT 2003


Here's my design problem:
When I start my app, I generate a seeries of lookup table objects (called
"registries") by parsing through a series of XML files. XML-RPC requests
come in requesting information and these registries are then used to help
fulfill the request. Periodically, albeit infrequently, one of the original
source XML files may change and an XML-RPC call will request that the
registries be updated/regenerated. During the regeneration process, which
could take multiple seconds, all lookup requests should block until
completion of the regeneration.

I am trying to determine if implementing these registries in ZODB will
provide this behavior. In particular:
1) What is the lookup behavior if I wrap the regeneration behavior in a
transaction? If I've started but not yet completed a transaction, do lookup
requests a) see the pre-transaction start registry objects or b) or block
(throwing an exception) or c) see the incomplete object in the midst of

2) If it doesn't block, is there a way I can make it (or at least return an
indicator that the results may be out of date)?

3) Once the transaction has completed successfully, do all copies of the
registries get updated immediately?

4) Am I barking up the wrong tree here - using the wrong tool/concepts to
solve this problem.

Thanks in advance for the help.


Stephen Nesbitt
Senior Configuration Management Engineer
The Cobalt Group
snesbitt at cobaltgroup.com

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