Windows Performance Counters

Back in the day of physical servers I created a document with this information in it from various places on the internet, I’ve kept it for years and most of the information included in it is still accurate. In the highly virtualized world we live in today this is only one part of performance troubleshooting and you have to be careful about some of the metrics, but the OS layer is still an important area to measure performance from. Adding virtualization to your environment does render any counter that has a time component to it (something/sec) since CPUs can be descheduled and their time skewed.

PAL (Performance Analysis of Logs)

http://pal.codeplex.com/

Windows Performance Analysis Developer Center

http://msdn.microsoft.com/en-us/performance/default.aspx

Performance Counter Thresholds

Memory\Available Mbytes

Threshold: A consistent value of less than 20 to 25 percent of installed RAM is an indication of insufficient memory.

Significance: This indicates the amount of physical memory available to processes running on the computer. Note that this counter displays the last observed value only. It is not an average.

Memory\Page Reads/sec

Threshold: Sustained values of more than five indicate a large number of page faults for read requests.

Significance: This counter indicates that the working set of your process is too large for the physical memory and that it is paging to disk. It shows the number of read operations, without regard to the number of pages retrieved in each operation. Higher values indicate a memory bottleneck.

If a low rate of page-read operations coincides with high values for Physical Disk\% Disk Time and Physical Disk\Avg. Disk Queue Length, there could be a disk bottleneck. If an increase in queue length is not accompanied by a decrease in the pages-read rate, a memory shortage exists.

Memory\Pages Input/sec

Threshold: The value should not exceed 15.  Higher the value poor the performance.

Significance:  Pages Input/sec is the rate at which pages are read from disk to resolve hard page faults. Hard page faults occur when a process refers to a page in virtual memory that is not in its working set or elsewhere in physical memory, and must be retrieved from disk.

Memory\Pages/sec

Threshold: Sustained values higher than five indicate a bottleneck.

Significance: This counter indicates the rate at which pages are read from or written to disk to resolve hard page faults. To determine the impact of excessive paging on disk activity, multiply the values of the Physical Disk\ Avg. Disk sec/Transfer and Memory\ Pages/sec counters.  If the product of these counters exceeds 0.1, paging is taking more than 10 percent of disk access time, which indicates that you need more RAM.  If this occurs over a long period, you probably need more memory.

A high value of Pages/sec indicates that your application does not have sufficient memory. The average of Pages Input/sec divided by average of Page Reads/sec gives the number of pages per disk read. This value should not generally exceed five pages per second. A value greater than five pages per second indicates that the system is spending too much time paging and requires more memory (assuming that the application has been optimized).

If the Pages / sec multiplied by 4,000 (the 4k page size) is greater than 70% of the total number of Logical Disk Bytes / sec to the disk(s) where the page file is located on a consistent basis then you should investigate.

Translation:  If paging to disk is > 70% of your total disk activity on a consistent basis then there may be an issue

PhysicalDisk\%Disk Time

Threshold:  Greater than 50 percent, it represents an I/O bottleneck

Significance: Represents the percentage of elapsed time that the selected disk drive was busy servicing read or write requests.

PhysicalDisk\Avg. Disk Queue Length

Threshold: Should not be higher than the number of spindles plus two.

Significance: This counter indicates the average number of both read and writes requests that were queued for the selected disk during the sample interval.

PhysicalDisk\Avg. Disk Read Queue Length

Threshold: Should be less than two.

Significance: This counter indicates the average number of read requests that were queued for the selected disk during the sample interval.

PhysicalDisk\Avg. Disk sec/Read

Threshold: No specific value.

  •          Less than 10 ms – very good
  •          Between 10-20 ms – okay
  •          Between 20-50 ms – slow, needs attention
  •          Greater than 50 ms – Serious I/O bottleneck

Significance: This counter indicates the average time, in seconds, of a read of data from the disk.

PhysicalDisk\Avg. Disk/Transfer

Threshold: Should not be more than 20 milliseconds.

Significance: This counter indicates the time, in seconds, of the average disk transfer. This may indicate a large amount of disk fragmentation, slow disks, or disk failures. Multiply the values of the Physical Disk\Avg. Disk sec/Transfer and Memory\Pages/sec counters. If the product of these counters exceeds 0.1, paging is taking more than 10 percent of disk access time, so you need more RAM.

PhysicalDisk\Avg. Disk Write Queue Length

Threshold: Should be less than two.

Significance: This counter indicates the average number of write requests that were queued for the selected disk during the sample interval.

PhysicalDisk\Disk Reads/sec & PhysicalDisk\Disk Writes/sec

Threshold: Depends on manufacturer’s specification.

Significance: This counter indicates the rate of write operations on the disk.

Processor\%Privileged Time

Threshold: A figure that is consistently over 75 percent indicates a bottleneck.

Significance: This counter indicates the percentage of time a thread runs in privileged mode. When your application calls operating system functions (for example to perform file or network I/O or to allocate memory), these operating system functions are executed in privileged mode.

Processor\%Processor Time

Threshold: The general figure for the threshold limit for processors is 65 percent.

Significance: This counter is the primary indicator of processor activity. High values many not necessarily be bad. However, if the other processor-related counters are increasing linearly such as % Privileged Time or Processor Queue Length, high CPU utilization may be worth investigating.

System\Context Switches/sec

Threshold: As a general rule, context switching rates of less than 5,000 per second per processor are not worth worrying about. If context switching rates exceed 15,000 per second per processor, then there is a constraint.

Significance: Context switching happens when a higher priority thread preempts a lower priority thread that is currently running or when a high priority thread blocks. High levels of context switching can occur when many threads share the same priority level. This often indicates that there are too many threads competing for the processors on the system. If you do not see much processor utilization and you see very low levels of context switching, it could indicate that threads are blocked.

2 thoughts on “Windows Performance Counters

  1. Pingback: Windows Performance Counters | Lewan & Associates IT Solutions Technical Blog

  2. Pingback: overloaded I/O subsystem in job description?

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