So far, I found there are some interesting ways to search in global structure:
InterSystems FAQ rubric
Data for InterSystems products (table row data, object instance data) is stored in global variables.
The data size of each global can be obtained by clicking the properties of the global you want to view from the Management Portal > System > Configuration > Local Database > Globals page, and then clicking the Calculate Size button on the Global Attributes page that appears.
To display the data sizes of globals in a namespace, you can call ^%GSIZE utility on the terminal.