The single-server out of the box SharePoint 2010 installation uses SQL Express, which comes with a 4 GB limit. This is in contrast to SharePoint 2007 which used the Windows Internal Database, a version of SQL Express with no size limit. If you’re upgrading an existing environment or planning to import a bunch of files, you may easily hit this limit.
Once this limit is reached, you’ll see errors like the following, when trying to do anything in SharePoint. I saw this error just trying to activate a feature. You’ll also get errors when tying to check out files or import new files.
Could not allocate space for object ‘dbo.EventCache’.’EventCache_Id’ in database
Some solutions to work around this are to switch to SQL Server, which doesn’t have a file size limit, or to try to implement remote BLOB storage. Getting the BLOBS out of SQL will significantly reduce the database size. If the environment is just a test environment, you could also delete enough files out of the database or move files to a different database.