Explanation
The database subsystem is used to communicate with external database servers and execute SQL queries from Unified CCX applications. The database subsystem is available only if the system has a license installed for either the Unified IP IVR or Unified CCX Premium product packages. If the database subsystem is not configured, it will show as out of service on the Control Center page of AppAdmin. This means that the database subsystem is not operational and cannot process any requests from the applications. To configure the database subsystem, you need to add database resources and specify the connection parameters for each database server that you want to access from your applications. You also need to enable the database subsystem from the Control Center page after adding the database resources. References: Cisco Unified Contact Center Express Administration Guide, Release 11.5 (1) - Database Subsystem Configuration

Explanation
Reactive debugging is a facility provided by the Cisco Unified CCX Editor that allows you to debug a Cisco Unified CCX script live with a real voice call. Reactive debugging enables you to step through the script execution and view the variable values and the call flow in real time. You can also set breakpoints and watchpoints to pause the script execution and inspect the variables. Reactive debugging is useful for troubleshooting and testing the script logic and functionality12 References: 1: Deploying Cisco Unified Contact Center Express (UCCXD) v6.0 - Course 644-906 1 2: Cisco Unified Contact Center Express Scripting and Development Series: Volume 2, Editor Step Reference, Release
10.0(1) - Debugging Scripts [Cisco Unified Contact Center Express] - Cisco

Explanation
According to the Cisco Unified Contact Center Express Design Guide, Release 8.0(1), Cisco Unified CCX 8.0 can support a maximum of 400 agents when deployed with Cisco Unified Communications Manager. This is the highest capacity option for Cisco Unified CCX 8.0, which requires a dedicated server for the Cisco Unified CCX Engine and a dedicated server for the Cisco Unified CCX Database.
The maximum number of agents depends on the hardware configuration, the deployment model, and the features enabled. For example, if Cisco Unified CCX is deployed in a high availability mode, the maximum number of agents is reduced to 300. If Cisco Unified CCX is deployed with Cisco Unified Presence, the maximum number of agents is reduced to 250. If Cisco Unified CCX is deployed with Cisco Unified Intelligence Center, the maximum number of agents is reduced to 150. The maximum number of agents also varies for different versions of Cisco Unified CCX. For example, Cisco Unified CCX 7.0 can support a maximum of 300 agents, while Cisco Unified CCX 9.0 can support a maximum of 500 agents. References: Cisco Unified Contact Center Express Design Guide, Release 8.0(1), Chapter
2: Unified CCX Product Overview, Section 2.1: Unified CCX Product Packages, Page 151 Cisco Unified Contact Center Express Design Guide, Release 8.0(1), Chapter 3: Unified CCX Architecture and Capacity Planning, Section 3.1: Unified CCX Deployment Models, Page 252 Cisco Unified Contact Center Express Design Guide, Release 8.0(1), Chapter 3: Unified CCX Architecture and Capacity Planning, Section 3.2: Unified CCX Capacity Planning, Page 293