PAGEIOLATCH_NL Wait Type Explained

PAGEIOLATCH_NL occurs when a thread acquires a Null mode latch on a page involved in an I/O operation. The Null latch mode is the least restrictive latch type in SQL Server's latch hierarchy and is compatible with all other latch modes. This wait type is extremely rare in practice and there is very little documented about it.

If PAGEIOLATCH_NL appears in your wait statistics, it is almost certainly benign background activity. It does not indicate a performance problem and does not require investigation or tuning. Simply filter it from your wait statistics analysis alongside other benign waits.

Verify PAGEIOLATCH_NL presence in current wait stats:

SELECT 
    wait_type,
    waiting_tasks_count,
    wait_time_ms,
    max_wait_time_ms,
    signal_wait_time_ms,
    CAST(wait_time_ms / 1000.0 AS DECIMAL(10,2)) AS wait_time_seconds
FROM sys.dm_os_wait_stats 
WHERE wait_type = 'PAGEIOLATCH_NL'
    AND waiting_tasks_count > 0;

Show actionable waits while filtering benign background waits:

WITH FilteredWaits AS (
    SELECT 
        wait_type,
        wait_time_ms,
        waiting_tasks_count,
        wait_time_ms - signal_wait_time_ms AS resource_wait_ms
    FROM sys.dm_os_wait_stats
    WHERE wait_type NOT IN (
        'PAGEIOLATCH_NL', 'BROKER_EVENTHANDLER', 'BROKER_RECEIVE_WAITFOR',
        'BROKER_TASK_STOP', 'BROKER_TO_FLUSH', 'CHECKPOINT_QUEUE',
        'CLR_AUTO_EVENT', 'CLR_MANUAL_EVENT', 'DISPATCHER_QUEUE_SEMAPHORE',
        'FT_IFTS_SCHEDULER_IDLE_WAIT', 'HADR_FILESTREAM_IOMGR_IOCOMPLETION',
        'KSOURCE_WAKEUP', 'LAZYWRITER_SLEEP', 'LOGMGR_QUEUE', 'MEMORY_ALLOCATION_EXT',
        'ONDEMAND_TASK_QUEUE', 'PREEMPTIVE_XE_GETTARGETSTATE', 'QDS_PERSIST_TASK_MAIN_LOOP_SLEEP',
        'QDS_ASYNC_QUEUE', 'QDS_CLEANUP_STALE_QUERIES_TASK_MAIN_LOOP_SLEEP'
    )
    AND waiting_tasks_count > 0
)
SELECT TOP 20
    wait_type,
    CAST(wait_time_ms / 1000.0 AS DECIMAL(10,2)) AS wait_seconds,
    waiting_tasks_count,
    CAST(resource_wait_ms / 1000.0 AS DECIMAL(10,2)) AS resource_wait_seconds
FROM FilteredWaits
ORDER BY wait_time_ms DESC;

No prevention is required for PAGEIOLATCH_NL waits since they represent normal background buffer pool operations. These waits indicate SQL Server's internal processes are functioning correctly and do not require tuning or intervention.

Modern monitoring tools like AutoDBA automatically filter benign waits from analysis, allowing DBAs to focus on actionable performance issues rather than harmless background noise. Include PAGEIOLATCH_NL in your standard benign wait filter lists to maintain accurate wait statistics baselines.