SharePoint 2010 can handle very large lists with millions of items. However, Effective indexing and throttling can be a very useful technique to improve performance of large lists. Be default SharePoint provide default settings for the sites limiting how much items/lookup fields can be retrieved per query. If you get the exception “Query exceeds lookup column threshold.” or “The query can not be completed because the number exceeds the contained Lookup enforced by the Administrator Lookup threshold.” you know that you have exceeded the lookup columns limitation imposed by your administrator.
If you have administrative permission then you can modify the limitations To modify the settings go to “SharePoint Central Administrator” => Application Management (from left side navigation) and then “Manage Web Application”. You’ll find the page shown below:
Figure 1: Web application lists
Now from the web application list select the web application you want to configure and then click “Resource Throttling” from the ribbon as shown below:
Figure 2: Resource Throttling menu
Finally change the max number of lookup columns as shown below:
After setting the value N for the lookup threshold you can at most include N numbers of lookup field in any query.