The Force.com Multitenant Architecture: Understanding the Design of Salesforce.com’s Internet Application Development Platform

Data Definition Processing

Certain types of modifications to the definition of an object require more than simple UDD metadata updates. In such cases, Force.com uses efficient mechanisms that help reduce the overall performance impact on the platform’s multitenant applications.

For example, consider what happens behind the scenes when someone modifies a column’s datatype from picklist to text. Force.com first allocates a new slot for the column’s data, bulk copies the picklist labels associated with current values, and then updates the column’s metadata so that it points to the new slot. While all of this happens, access to data is normal and applications continue to function without any noticeable impact.

As another example, consider what happens ...