The code in createDropboxCollection() in BaseContentService.java iterates through every user in the site to attempt to create a dropbox if the user doesn't exist.
Thus for every site save operation (e.g. update site properties, add users, etc.), a sql query is generated like:
select XML from CONTENT_COLLECTION where ( COLLECTION_ID = '/group-user/siteid/userid/')
This is a scaleability issue for large sites and generates unnecessary db traffic and app server overhead (even for smaller sites).
The entire collection of dropboxes for the site should be read in with one query, viz.
select XML from CONTENT_COLLECTION where IN_COLLECTION = '/group-user/siteid/'
and only additions, deletions or updates written to the db.