The "query governor cost limit" configuration in SQL Server is a setting that allows users to define a threshold for the estimated query cost in terms of query execution units (QEs). When a query is submitted to SQL Server, the query optimizer estimates the cost of executing the query based on factors such as the complexity of the query, the number of rows involved, and the available indexes. If the estimated cost of a query exceeds the specified limit set by the "query governor cost limit," SQL Server will prevent the query from executing to avoid potential performance issues.
Explanation
- The "query governor cost limit" configuration helps control the execution of queries in SQL Server by setting a limit on the estimated cost of a query.
- The query optimizer generates a query plan and estimates the cost of executing the query based on various factors such as the number of rows, joins, sorts, and available indexes.
- If the estimated cost of a query exceeds the threshold defined by the "query governor cost limit," SQL Server will abort the query execution to prevent resource-intensive queries from impacting system performance.
Security Risks
While the "query governor cost limit" configuration is primarily focused on query performance management, there are potential security risks to consider:
- Denial of Service (DoS): Malicious users could attempt to launch denial of service attacks by submitting resource-intensive queries that exceed the "query governor cost limit," causing legitimate queries to be blocked and potentially impacting system availability.
- SQL Injection Attacks: Sophisticated attackers may attempt to bypass query governor restrictions by crafting queries that evade the cost limit threshold, potentially exploiting vulnerabilities in the SQL Server instance.
- Information Leakage: Setting overly permissive or restrictive values for the "query governor cost limit" could inadvertently expose sensitive information about query execution plans or database structures, leading to potential information leakage.
- Performance Degradation: In scenarios where the "query governor cost limit" is set too low or too high, there is a risk of impacting query performance, system responsiveness, and overall database operations, potentially leading to user dissatisfaction or system inefficiency.
Recommendations
To mitigate security risks associated with the "query governor cost limit" configuration in SQL Server, consider the following best practices:
- Set the "query governor cost limit" to an appropriate threshold that balances query performance with resource utilization, taking into account the complexity and workload of the database environment.
- Optimize queries and indexes to improve query performance and reduce the likelihood of queries exceeding the cost limit threshold.
- Implement monitoring tools to track query execution times, costs, and resource utilization, and audit query governor events to detect potential security incidents or unauthorized query activities.
- Restrict access to the "query governor cost limit" configuration to authorized users with appropriate permissions to prevent unauthorized changes that could impact query execution and system performance.
By following these best practices and carefully managing the "query governor cost limit" configuration in SQL Server, organizations can effectively control query performance, prevent resource-intensive queries from impacting system stability, and mitigate security risks related to denial of service attacks, SQL injection vulnerabilities, information leakage, and performance degradation.