Essential ASP.NET Performance Counter

For list of others essential performance counters for applications based on Windows platform see here.

When there is a requirement of collecting performance counters during performance testing, it becomes tough to select few counters from existing many.  All counters are important in its context and cannot be simply ignored.  So, it is very important to recheck the list of counters that needs to be monitored before every performance run.  You might need to change the counters as per yours requirements.

Following are some of the ASP.NET counters, that I find bare essential to start with though.  These counters are related to specific web applications and not system wide, which have been ignored intentionally.  The list of counters and its preferred  / threshold values are being collected from multiple relevant blogs / links and have been mentioned in the ‘References’ section below.

Performance Object	Performance Counter	Preferred Value
Cache API Counters	Cache API Hit Ratio	> 80%
	Cache API Turnover Rate	None
Errors Counters	Errors during Execution	None
	Errors Unhandled During Execution/sec	None
Output Cache Counters	Output Cache Hit Ratio	None
	Output Cache Turnover Rate	None
Requests Counters	Requests in Application Queue	None
	Requests / sec	None
Miscellaneous Counters for ASP.NET Applications	Pipeline Instance Count	None

Cache API Counters

Cache API Hit Ratio

It indicates ratio of cache hits to misses of objects called from user code.

Preferred Value:  Greater than 80%

Threshold Value:  See preferred value

Notes:

1. A low ratio can indicate inefficient use of caching techniques in the program.
2. This counter does not track use of the cache internally by ASP.NET
3. With sufficient RAM, you should normally record a high (greater than 80 percent) cache hit ratio.

 Cache API Turnover Rate

The number of additions to and removals from the cache per second, when it is used through the external APIs (excluding internal use by the ASP.NET framework)

Preferred Value:  None

Threshold Value:  None

Notes:

1. A high turnover rate indicates that items are being quickly added and removed, which can be expensive.
2. High turnover suggest inefficient utilization of cache.  Cache API hit ratio can be greater than 90% but if turnover rate is high then it's an indication of inefficient utilization of cache.

Errors Counters

Errors during Execution

The total number of errors that occurred during the execution of an HTTP request

Preferred Value:  None

Threshold Value:  None

Notes:

1. It excludes parser and compilation errors though.
2. It indicates failure during run-time and should be monitored.
3. Correlate it with ‘Errors Unhandled during Execution / sec’ to find out if application is handling negative flows with the help of catching / throwing exceptions.

Errors Unhandled During Execution/sec

The total number of unhandled exceptions per second at run time

Preferred Value:  None

Threshold Value:  None

Notes:

1. Unhandled exceptions are more problematic in terms of performance.

Output Cache Counters

Output Cache Hit Ratio

The percentage of total requests that were serviced from the output cache

Preferred Value:  None

Threshold Value:  None

Notes:

1. The total hit-to-miss ratio of Output Cache requests.

Output Cache Turnover Rate

It indicates the number of additions and removals to the output cache per second

Preferred Value:  None

Threshold Value:  None

Notes:

1. A high turnover rate indicates that items are being quickly added and removed, which can be expensive.

Requests Counters

Requests in Application Queue

The number of requests in the application request queue

Preferred Value:  None

Threshold Value:  None

Notes:

1. In addition to Requests Current, Requests in Application Queue provides a warning for when requests will be rejected.
2. If there are only a couple virtual directories, increasing the default appRequestQueueLimit to 200 or 300 may be suitable, especially for slow applications under heavy load.
3. Presence of queue most of the time suggests performance issues, so if queue is not decreasing or increasing further investigation is required.

Requests/sec

The average number of requests that have been executed per second

Preferred Value:  None

Threshold Value:  None

Notes:

1. This counter represents the current throughput of the application.
2. Correlate this counter with number of requests from clients and find out if it is decreasing / increasing accordingly. If not, then it needs to be analyzed.

Miscellaneous Counters for ASP.NET Applications

Pipeline Instance Count

The number of active request pipeline instances for the specified ASP.NET application.  It represents the maximum number of concurrent requests that are being processed for a specific application.

Preferred Value:  None

Threshold Value:  None

Notes:

1. Only one execution thread can run within a pipeline instance, this number represents the maximum number of concurrent requests that are being processed for a specific application.
2. In most circumstances, it is better for this number be low when the server is busy, because this means that the CPU is well used.
3. The number of pipeline instances should be steady. Sudden increases are indicative of back end latency.

References:

    1.  IIS

   2. ASP.NET Performance Monitoring, and When to Alert Administrators

    3.  Performance Counters for ASP.NET

    4.  How ASP.NET Works

   5.  Measuring .NET Application Performance