IO Latency in SQL Server
Introduction
Query Overview
I/O latency Range
Conclusion
Introduction
Are you experiencing slow database performance and suspect it's due to I/O latency? Understanding the input/output (I/O) operations of your database is crucial for
optimizing performance. In this blog, we'll explore a SQL query that provides detailed insights into database I/O latency using SQL Server.
Query Overview
This SQL query retrieves information from the
sys.dm_io_virtual_file_stats dynamic management view, providing details about I/O latency for the current database.
Let's break down the key components of the query:
- vfs.database_id: The ID of the database.
- db_name(vfs.database_id):The name of the database.
- fs.file_id:The ID of the file.
- fs.name:The logical name of the file.
- fs.type_desc: The type of file (e.g., data file, log file).
- fs.physical_name: The physical name of the file.
- vfs.num_of_reads:The number of read operations.
- vfs.io_stall_read_ms: The total time, in milliseconds, that read operations have been stalled.
- vfs.io_stall_average_read_ms:The average stall time per read operation.
- vfs.num_of_writes: The number of write operations.
- vfs.io_stall_write_ms: The total time, in milliseconds, that write operations have been stalled.
- vfs.io_stall_average_write_ms: The average stall time per write operation.
use YourDBName
select
vfs.database_id,
db_name(vfs.database_id) database_name,
fs.file_id,
fs.name,
fs.type_desc,
fs.physical_name,
fs.size,
vfs.sample_ms,
vfs.num_of_reads,
vfs.num_of_bytes_read,
vfs.io_stall_read_ms,
vfs.io_stall_read_ms * 1.0 / vfs.num_of_reads * 1.0 as io_stall_average_read_ms,
vfs.io_stall_queued_read_ms,
vfs.num_of_writes,
vfs.num_of_bytes_written,
vfs.io_stall_write_ms,
vfs.io_stall_write_ms * 1.0 / vfs.num_of_writes * 1.0 as io_stall_average_write_ms,
vfs.io_stall_queued_write_ms,
vfs.io_stall,
vfs.size_on_disk_bytes,
vfs.file_handle
from
sys.dm_io_virtual_file_stats(db_id(), null) as vfs
inner join
sys.database_files as fs
on vfs.file_id = fs.file_id
where
vfs.num_of_reads > 0
or
vfs.num_of_writes > 0
order by
type_desc,
io_stall_average_read_ms desc;
By executing this query, you can gain insights into the I/O performance of your database, helping you identify potential bottlenecks and optimize performance.
Whether it's analyzing read/write operations, identifying high latency issues, or optimizing disk usage, this SQL query provides valuable information for
database administrators and developers alike.
I/O latency Range
Typical I/O latency could fall into the following ranges:
Range | Latency
---------------|----------------
Excellent | < 1ms
Very good | < 5ms
Good | 5ms – 10ms
Poor | 10ms – 20ms
Bad | 20ms – 100ms
Shockingly bad | 100ms – 500ms
WOW! | > 500ms
Conclusion
In conclusion, understanding database I/O latency is essential for maintaining optimal performance. By utilizing SQL Server's dynamic management views and
executing the provided SQL query, you can effectively analyze and optimize your database's I/O operations, leading to improved performance and better overall
user experience.
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