We are recently have a time out issue from database when browsing a large SharePoint 2007 list (approx. 300K items).
To solve the problem, we have tried following things:
1. increase database time out value by stsadm command:
Stsadm –o setproperty –pn database-connection-timeout –pv 120
2. make sure all filtered, and sorted columns on list views are indexed.
3. make sure RowLimit has been set on all views and custom codes. The RowLimit value should be less than 1000, otherwise, SQL server seems locking whole UserData table on select statement.
4. The anti-virus should be turned off on SQL server, or excluded from scanning SQL data files.
5. make sure SQL server maintenance plans are proper configured, such as maintenance plans for re-index, update statistics on content databases.