Understanding the Basics of Collaboration in SharePoint 2010 : Advanced List Concepts (part 1) - Large List Support, Site Columns

Additional features in SharePoint 2010 lists allow for additional customization and administration of list data. By providing support for large lists, site columns, and advanced input forms, site administrators are able to control not only the data into the list, but server resources, global farm access to list data, and the methods users use to enter data into lists.

1. Large List Support

SharePoint has traditionally been able to support large lists; however, the challenge has always been to make the data in large lists available for retrieval and display in a timely and efficient manner. Although a user can create millions of items in a SharePoint list, the query operation slows as the size of the list grows. A new addition to SharePoint 2010 is large list support throttling. Throttling allows farm administrators to set manageable limits on the number of items queried from a SharePoint 2010 list. Using throttling, SharePoint 2010 encourages developers and farm administrators to control large list queries to improve the performance of a SharePoint farm.

Throttling thresholds are set on site collections. By default, standard users are throttled at 5000 items returned from a list, with a warning threshold at 3000 items. (See Table 1 for a list of items that would be throttled.) These values can be changed using Windows PowerShell commands. The throttling mechanic works as follows: If a user is pulling back a list with 4999 items, the query returns all of the data without error; however, if the user or query tries to retrieve 5001 items, an expensive query exception will be returned. The following parameters are set by default.

• Warning for user throttling at 3000 items

• Standard user throttling at 5000 items

• Super user throttling at 20,000 items

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Note:

Developers can request a throttle override from the Object Model by using SPQuery.RequestThrottleOverride and SPSiteDataQuery.RequestThrottleOverride, which will effectively cause SharePoint to ignore the throttling behavior.

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Table 1. Items Throttled for a Standard User with Large List Support Throttling

NUMBER OF ITEMS RETURNED	QUERY RUN IN NORMAL LIST AS STANDARD USER
<5000 list items	Code and/or view query will run and return the required result.
>3000 list items	No exception is thrown and the code will run properly.
>5000 list items	An expensive query exception is thrown.
>5000 list items during time window OK for large queries	Query threshold is not applied, query runs even if the threshold has been exceeded.
Object Model Override = true and RequestThrottleOverride is overridden	Exception is thrown if list is throttled, and this property cannot be overridden by a normal user.

Using Central Administration, a farm administrator can configure a time frame in which these expensive queries can and cannot be run. Therefore, if a user wants to run a query with 5001 items at 5:30 P.M. and the time-frame limitation is between 8:00 A.M. and 5:00 P.M., the query would succeed. To see if a list is being throttled or within warning limits, go to List Settings and look at the bar that gives the number of items in the view/list.

To find out the current throttling limits, follow these steps.

1. Open a browser and go to the SharePoint Central Administration website.

2. Under Application Management, select Manage Web Application.

3. Select the Web application that you want to modify or view.

4. Click General Settings in the Ribbon and select Resource Throttling. Figure 1 shows the Central Administration Resource Throttling command on the General Settings menu.

   Figure 1. Resource Throttling

   

Figure 2, which displays list resource throttling parameters, is the first of several pages of information you will see with resource throttling settings. A farm administrator should be familiar with these settings before any changes are made to a SharePoint site. Also, it’s important to test all new settings in a development environment before applying configuration changes in production.

Figure 2. List Resource Throttling parameters

An Upgrade Warning: Setting Throttle Limits When upgrading from SharePoint Server 2007 to SharePoint 2010, any list that contains a default view of more than the throttled limit (default: 5000) will not be immediately available until a new default view is created. A farm administrator should become familiar with the Windows PowerShell commands, which will display and set the throttling limits. These commands are listed in Table 2, with examples. Table 2. Windows PowerShell Commands for Displaying and Setting Throttling Limits COMMAND DESCRIPTION EXAMPLE COMMAND Get max threshold values for Web application $sitecol = Get-SPSite http://mysharepointserver:5000 $sitecol.WebApplication.MaxItemsPerThrottledOperationWarningLevel $sitecol.WebApplication.MaxItemsPerThrottledOperation $sitecol.WebApplication.MaxItemsPerThrottledOperationOverride $sitecol.WebApplication.AllowOMCodeOverrideThrottleSettings Get max threshold values for Web application—example usage $sitecol = Get-SPSite http://mysharepointserver:5000 $sitecol.WebApplication.MaxItemsPerThrottledOperationWarningLevel = 2000 (set throttle warning to 2000 items – default 3000) $sitecol.WebApplication.MaxItemsPerThrottledOperation = 4000 (set throttle to 4000 – default 5000) $sitecol.WebApplication.MaxItemsPerThrottledOperationOverride = 30000 (set super user throttle to 30000 – default 20000) $sitecol.WebApplication.AllowOMCodeOverrideThrottleSettings = False (set code override for throttling to False – default True) Note: Values in this section are for example purposes and are not recommendations Find large list throttle setting $siteCollection.RootWeb.Lists[“LargeListName”] (look for IsThrottled in results)

In summary, SharePoint 2010 large list support will support lists with

• Up to 50 million items—during read operations

• Configuration options for administrators per Web applications

• Privileged operational override support for users with site collection or list administration privileges

• Default query restrictions

• Throttling when a list reaches a predefined of items

2. Site Columns

In traditional database application development, calls are often necessary that refer to a set of table data multiple times during the application execution. By having a single authoritative source for data, applications can ensure consistency across all application modules. This is often true in SharePoint as well—to keep consistency across the SharePoint farm, a cross-site lookup column is required in some cases. Cross-site lookups cannot be done using a standard lookup column, however, so a site column should be used instead.

Site columns are defined at the site collection level and are accessible to all sites under the site collection. A few common examples of standard SharePoint site columns are FTP Site and Gender. The FTP Site column is a URL field in which a URL and description can be entered; a Gender column provides the user a choice of Male or Female. In both cases, there is no ambiguity about what the user will need to type across all SharePoint sites. The primary advantage of using a site column is its ability to provide a consistent user response for the column.

To link to an existing site column, complete the following steps.

1. Click List under the List Tools tab and then select List Settings.

2. Click Add From Existing Site Columns.

3. Select the site group All Groups.

4. Select the FTP Site column from Available Site Columns.

5. Click Add and then click OK.

2.1. Creating a Site Column

To create a new site column in SharePoint 2010 from the root of the site collection, complete the following steps.

1. Click Site Actions in the Ribbon and select Site Settings.

2. Click Site Columns under Galleries.

3. Click Create. You will see a new page that you use to create the column, setting the title, settings, and validation as necessary. When you have finished selecting the settings for the new site column, click OK.

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Note:

If, as the site administrator, you plan on creating many new columns, you should consider creating a new Site Column Group.

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2.2. Modifying a Site Column

To modify an existing site column in SharePoint 2010 from the root of the site collection, complete the following steps.

1. Click Site Actions in the Ribbon.

2. Click Site Columns under Galleries.

3. Click the site column you want to modify.

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   Note:

   As with lists, only certain changes to the list type are supported, and content might be lost when converting from one type to another, such as going from a multiple lines of text type to a single line of text.

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4. Change or edit the group if needed.

5. Change settings as needed.

6. Set the Update All Columns Based Upon This Site Column option to Yes to update all of the site columns. This operation can take a while to run, and any customizations to child list settings might be lost.

7. Click OK.