Optimizing Performance and Security: A Guide to Connection Pooling and Audit Logs in SQL Server

Here's a breakdown to clarify the situation:

Real Login vs. Pooled Login:

• Real Login: When an application first requests a connection and it's not available in the pool, a new connection is established with the server. This triggers a real login event, reflected in the logs.
• Pooled Login: Subsequent connection requests often use existing connections from the pool. This doesn't involve creating a new connection with the server, but rather reusing an existing one. However, an Audit Login event is still generated, even though it's a pooled connection, not a real login.

Identifying Pooled Logins:

The "EventSubClass" column in the Audit Login event details can help distinguish between real and pooled logins. This column might not be visible by default, but you can enable it during trace setup ().

• Value 1: Indicates a real login (new connection established)
• Value 2: Indicates a pooled login (existing connection reused)

Example:

Imagine an application that retrieves data every minute. Here's how connection pooling and Audit Login/Logout behave:

• First Call: The application requests a connection - a real connection is established (EventSubClass = 1) and logged as Audit Login.
• Second Call (and subsequent): The application requests another connection - it retrieves a connection from the pool (EventSubClass = 2) and still triggers an Audit Login event, even though it's not a real login in the traditional sense.

Related Issues and Solutions:

• Misinterpreting Pooled Logins: Seeing frequent Audit Login/Logout events, especially with connection pooling, might lead to the mistaken belief that logins are happening excessively. Analyzing the "EventSubClass" column helps clarify this.
• Excessive Real Logins: If you suspect genuinely high login activity, connection pooling might not be the cause. Investigate your application logic or potential security concerns.