PREEMPTIVE_OS_CRYPTIMPORTKEY Wait Type in SQL Server

Understanding the PREEMPTIVE_OS_CRYPTIMPORTKEY Wait Type in SQL Server

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SQL Server uses a wide variety of wait types to track what a query is waiting on before it can continue executing. One of these wait types, PREEMPTIVE_OS_CRYPTIMPORTKEY, can be challenging to understand and troubleshoot. This discussion will provide a deep dive into what this wait type means, why it occurs, and how it impacts performance in SQL Server.

What Are Wait Types in SQL Server?

Before understanding the specifics of PREEMPTIVE_OS_CRYPTIMPORTKEY, it’s important to have a general understanding of wait types in SQL Server. Every time a query runs, it may encounter situations where it must wait before it can proceed. These wait types help database administrators diagnose performance bottlenecks by revealing where a process is stalling.

Common reasons for waits include:

• Waiting for locks to be released (e.g., blocking issues)
• Waiting for disk I/O to complete
• Waiting for network communication
• Waiting for external system resources

When a query enters a wait state, it is not actively using CPU resources. Instead, it remains idle until the resource it is waiting on becomes available.

What is PREEMPTIVE_OS_CRYPTIMPORTKEY?

The PREEMPTIVE_OS_CRYPTIMPORTKEY wait type specifically occurs when SQL Server is waiting for the operating system to import a cryptographic key. This process happens when a query uses encryption-related functions such as:

• ENCRYPTBYKEY – Encrypts data using a symmetric key
• DECRYPTBYKEY – Decrypts encrypted data
• OPEN SYMMETRIC KEY – Opens a symmetric key for use in encryption
• Transparent Data Encryption (TDE) operations
• Column-level encryption using SQL Server’s built-in encryption features

When SQL Server executes encryption-related operations, it must interact with the Windows operating system to handle cryptographic keys. This interaction can introduce delays, especially if the encryption process is resource-intensive.

Why is PREEMPTIVE_OS_CRYPTIMPORTKEY a “Preemptive” Wait?

The keyword “PREEMPTIVE” in this wait type indicates that SQL Server is performing an operation outside of its usual execution context. Normally, SQL Server runs in a cooperative scheduling model, meaning tasks voluntarily yield CPU resources when needed. However, in a preemptive wait, SQL Server hands control over to the operating system, allowing it to complete the task before SQL Server can continue execution.

In the case of PREEMPTIVE_OS_CRYPTIMPORTKEY, SQL Server is waiting for the Windows OS to finish importing a cryptographic key, a process that SQL Server itself cannot directly control.

Performance Impact of PREEMPTIVE_OS_CRYPTIMPORTKEY

Frequent or prolonged occurrences of PREEMPTIVE_OS_CRYPTIMPORTKEY waits may indicate performance issues related to encryption. Some potential causes include:

• Heavy use of encryption functions: Queries frequently encrypting or decrypting large volumes of data can introduce latency.
• Inefficient key management: If encryption keys are not efficiently stored and accessed, SQL Server may experience repeated delays while importing keys.
• High CPU usage: Encryption and decryption are CPU-intensive tasks, and inadequate processing power can slow down operations.
• Slow disk performance: If encryption keys are stored on slow disks or require frequent retrieval from external sources, it can introduce additional delays.

How to Optimize Performance and Reduce PREEMPTIVE_OS_CRYPTIMPORTKEY Waits

If you are seeing a high number of PREEMPTIVE_OS_CRYPTIMPORTKEY waits, consider the following optimizations:

• Optimize Encryption Usage:
  • Avoid encrypting entire columns if only a subset of data requires encryption.
  • Use indexed columns for filtering instead of encrypted columns where possible.
• Use Transparent Data Encryption (TDE) Wisely:
  • Ensure that the TempDB database is stored on fast storage, as TDE encryption affects TempDB operations.
  • Monitor BACKUP performance, as encrypted BACKUPs can take longer to process.
• Review Key Management Strategies:
  • Ensure that symmetric keys are not frequently opened and closed unnecessarily in queries.
  • Use secure but efficient key storage solutions to avoid frequent retrieval delays.

Final Thoughts

The PREEMPTIVE_OS_CRYPTIMPORTKEY wait type occurs when SQL Server waits for the operating system to import a cryptographic key, typically during encryption and decryption processes. While encryption is crucial for data security, excessive or inefficient use can introduce performance challenges.

If your SQL Server instance is experiencing high PREEMPTIVE_OS_CRYPTIMPORTKEY waits, it’s essential to analyze encryption usage, optimize key management, and ensure that hardware and storage configurations are aligned for performance.

For a detailed evaluation of your SQL Server’s Performance and to identify potential bottlenecks, consider a SQL Server Health Assessment from Stedman Solutions. Our expert team can help diagnose and resolve performance issues, ensuring your SQL Server runs efficiently while maintaining robust security.

Need help with this wait type or others, Stedman Solutions can help. Need performance help, we can help with a comprehensive performance assessment? Need help on an ongoing basis, our managed services can help.Find out how Stedman Solutions can help you with a free no risk 30 minute consultation with Steve Stedman to find out how we can best help with your SQL Server needs.

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