Wait Type PAGEIOLATCH_NL

Wait statistics, in the context of SQL Server, refer to the amount of time that a query spends waiting to access data in the database. When a client application requests data from the database, the request is placed in a queue and the client application must wait for its turn to access the data. The time that the query spends waiting is called a "wait" and is tracked by SQL Server. This information can be used to identify potential performance bottlenecks and optimize the performance of the database. Wait statistics are commonly used by database administrators to diagnose and troubleshoot performance issues in SQL Server.

SQL Server provides a variety of wait types to help identify delays in query execution and resource access. The PAGEIOLATCH_NL wait type occurs when SQL Server threads are waiting for a non-locking latch on a data page that needs to be read from disk into memory. This wait type is typically related to disk I/O operations and can provide valuable insight into the health of your storage subsystem.

What Is the PAGEIOLATCH_NL Wait Type?

The PAGEIOLATCH_NL wait type appears when SQL Server needs to access a page that is not yet in memory and must be fetched from disk. Non-locking latches are used to coordinate this process without holding up other threads unnecessarily. However, if this wait type occurs frequently or for long durations, it could indicate issues with disk performance or query optimization.

When Does PAGEIOLATCH_NL Appear?

This wait type is commonly encountered in the following scenarios:

• High I/O Workloads – Queries requiring large amounts of data from disk can lead to increased PAGEIOLATCH_NL waits.
• Insufficient Memory – If the buffer pool is too small to hold frequently accessed data, SQL Server must read more pages from disk.
• Fragmented Indexes – Poorly maintained indexes can result in inefficient disk access patterns.
• Large Table Scans – Queries scanning large tables without proper indexing can trigger high disk reads.

Why PAGEIOLATCH_NL Waits Matter

While some PAGEIOLATCH_NL waits are expected in database systems, excessive or prolonged waits can negatively impact performance. Common causes include:

• Slow Storage – Disk subsystems that cannot keep up with SQL Servers read requests can increase wait times.
• Under-Provisioned Memory – Insufficient RAM can force SQL Server to rely more heavily on disk I/O.
• Suboptimal Query Design – Inefficient queries that access more data than necessary can increase disk read operations.
• Fragmented Data – Fragmentation in tables or indexes can lead to additional disk I/O overhead.

How to Address PAGEIOLATCH_NL Waits

If this wait type is affecting performance, consider these strategies:

• Optimize Queries – Ensure queries are efficient, using appropriate filters and indexes to reduce unnecessary data access.
• Increase Memory Allocation – Allocate more memory to SQL Server to expand the buffer pool and reduce disk reads.
• Improve Disk Performance – Use faster storage systems, such as SSDs, to decrease read latency.
• Maintain Indexes – Regularly rebuild or reorganize indexes to reduce fragmentation and improve data retrieval efficiency.
• Monitor Table Scans – Identify and address queries performing full table scans, often by implementing proper indexing.

Monitoring PAGEIOLATCH_NL Waits

To monitor this wait type and its impact on your SQL Server environment, use the Historic Waits Monitoring feature in Database Health Monitor. This tool tracks wait statistics over time, helping you pinpoint trends and identify performance bottlenecks. By proactively addressing these waits, you can ensure smoother query execution and better overall system performance.

Stedman Solutions specializes in SQL Server performance tuning and troubleshooting. If you’re dealing with PAGEIOLATCH_NL waits or other SQL Server challenges, our Database Health Monitor provides detailed insights, and our managed services deliver expert support to keep your SQL Server running at its best. Contact us today to learn how we can help improve your SQL Server performance and reliability.

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Applies to

Related Waits

See Also

• More About PAGEIOLATCH_NL