You are creating an ASP.NET page for selling movie tickets. Users select a region and then a city, and the site displays a list of theaters from a database table. To minimize the time required to retrieve and display the theater list for each region and city combination, which caching strategy should you configure on the page?

Introduction / Context:
ASP.NET provides output caching to reduce the load on the web server and database by storing rendered page output in memory. When the same page is requested multiple times with the same parameters, ASP.NET can return the cached version instead of executing the full data retrieval and rendering process again. In scenarios where users repeatedly select combinations of region and city to view theater information, output caching can significantly reduce response times and database activity.

Given Data / Assumptions:

The application uses an ASP.NET page that displays movie theater information based on a selected region and city.
Region and city are likely represented by server side controls, such as DropDownList controls named region and city.
The theater data is stored in a database table managed by the company.
Users often request the same region and city combinations, so caching can be very effective.
You want to minimize data retrieval time without complicating the database connection configuration.

Concept / Approach:
An OutputCache directive can cache the rendered output of a page based on varying parameters or control values. When using server side controls whose selected values determine the data shown, VaryByControl is especially useful. By setting VaryByControl=\"region;city\", the page output is cached separately for each unique pair of region and city values. Subsequent requests with the same selections are served from the cache, bypassing the database query. Adjusting packet size or shrinking the connection pool does not directly address the core performance requirement, which is to avoid repeated queries for the same parameter combinations.

Step-by-Step Solution:
1. Identify the controls that influence the data displayed on the page. In this case, the region and city selection controls determine which theater records are shown. 2. Add an OutputCache directive at the top of the ASP.NET page. For example: <%@ OutputCache Duration=\"60\" VaryByControl=\"region;city\" %>. 3. Set a Duration value appropriate for how often theater data changes. A longer duration means more caching, but you must balance this with the need for up to date information. 4. When a user selects a region and city and requests the theater list, the page is rendered, and the output is cached using the specific combinations of control values. 5. Subsequent requests with the same region and city within the cache duration are served from memory, avoiding repeated database hits and reducing response time.

Verification / Alternative check:
You can instrument the page to log database queries and then compare the number of hits before and after enabling output caching. With VaryByControl properly set, you should see fewer repeated queries for the same region and city combinations. Documentation on ASP.NET caching confirms that VaryByControl is designed for scenarios where control values drive page content.

Why Other Options Are Wrong:
Adjusting the packet size in the connection string affects network packet fragmentation but does not eliminate repeated queries and typically does not provide a major performance gain in this scenario.
Using VaryByParam=\"*\" caches based on all query string or form parameters, which may not align with server side control usage and can be less precise when the key variables are controls rather than raw parameters.
Reducing the database connection pool size can actually harm performance by causing more connection creation overhead and does not minimize the number of queries.

Common Pitfalls:
Developers sometimes focus too much on connection string tuning or hardware upgrades when caching would yield more significant performance improvements. Another pitfall is misusing caching by not varying the cache on the key parameters, which can cause incorrect data to be shown to users. Always identify the parameters or controls that drive data selection and configure VaryByParam or VaryByControl appropriately.

Final Answer:
You should add an OutputCache directive that uses VaryByControl=\"region;city\" so each region and city combination has its own cached page output.