"Zope 2.3.1b2 contains a number of bug fixes, including the
fixes for the issues addressed by the 02/23 and 03/08 hotfixes. It
also contains a number of changes to address issues with ZCatalog.
New data structures have been introduced to reduce the number of
conflict errors caused by object indexing under some types of
usage, and to reduce the amount of object database bloat that
occurs when indexed objects change frequently."
"The changes to ZCatalog have been designed so that newly
created ZCatalog objects will take advantage of the new data
structures. Existing ZCatalog objects will continue to work with
the old data structures, but will not gain any of the benefits of
the new code. It is possible to upgrade an existing ZCatalog object
to use the new data structures by following the How-To...."