Monitoring and Tuning Your Server

Useful Counters for Stress Testing

The following three tables list counters that provide a good indication of the health of a Web application during a stress test. Start with these counters, and add more to drill down to the cause of a bottleneck or resource leak. (The “Computername” parameter is omitted from the counters listed in these tables in order to save space.)

Table 5.16 Useful Counters for Monitoring Web Server Performance

Object	Counter	Purpose/Description
Web Service	Maximum Connections	The maximum number of simultaneous connections to the Web service. Use this number to determine the total number of concurrent connections a server experienced during a test run. If this number grows throughout a test, this is a good indication of a blocking backend dependency.
Web Service	Bytes Total/sec	Shows the sum of bytes sent and received by the HTTP service. If this number is low, it means that IIS 5.0 is not transferring data at a reliable rate. Both ASP pages and HTTP content transfer bytes.
Web Service	Current Connections	Shows the current number of connections to the service. This is the sum of both nonanonymous (authenticated) and anonymous (unauthenticated) users. If this number is at or near the maximum connections allowable, the Web service is at full capacity. Check the Web Site property page for this limit.
Web Service	Current NonAnonymous Users	The number of authenticated users currently connected to the HTTP Server. Use this number to determine the number of authenticated connections the Web server is seeing. If this is not greater than 0 during an authenticated stress run, confirm that you are using valid user accounts and that the appropriate permissions are being applied to the Web content.
Web Service	Not Found Errors	Shows the number of pages that are displaying an HTTP 404 result code to client. Anything greater than 0 is an indication of an invalid test run, because the test script is requesting pages that do not exist.
Active Server Pages	Errors/sec	The number of errors per second, including connection errors, compile errors, and run-time errors. If this number is greater than 0, something is wrong with the test scripts, server configuration, or scripts in ASP pages.
Active Server Pages	Requests/sec	The number of ASP page requests executed per second. Use this number to provide an indication of how heavy the stress on the Web server is. This number does not include HTTP requests and will fluctuate considerably based on the complexity of the ASP pages and the capacity of the Web server.
Active Server Pages	Request Not Found	Unlike the Web Service\ Not Found Errors, this shows only the ASP pages that were not found. These pages display as an HTTP 404 result code to the client. Anything greater than 0 is an indication of an invalid test run, because the test script is requesting pages that do not exist.
Active Server Pages	Requests Rejected	The total number of requests not executed because the queue was full or there were insufficient resources to meet the number of hits that the Web server is seeing. If this number is greater than 0, the stress test is too heavy, or the ASP pages are too complex.
Active Server Pages	Memory Allocated	The total amount of memory currently allocated by ASP. Compare this number to Memory\ Available Bytes and Memory\ Committed Bytes to determine what percentage ASP is using. A ratio of greater than 50 percent during the test would indicate a memory leak in a Server-Side Object.
Active Server Pages	Requests Queued	This should remain close to 0 but it will go up and down when testing a heavily scripted ASP page. The maximum number for this counter varies by the number of processors on the machine and the metabase setting for AspRequestQueueMax. If the limit is reached, your browser will display “HTTP/1.0 Server Too Busy.” If this queue grows rapidly as more stress is applied, this indicates that the ASP pages are too complex for the load.
Active Server Pages	Errors During Script Run Time	This is a count of errors that occurred in the ASP pages you are requesting. This should always be 0. If it sporadically shows a value greater than 0, look at the IIS 5.0 log to see which page is causing the problem and check for the error that occurred. If you have the registry set to capture these, the event log will also display the error.
Memory	Page Faults/sec	Displays the number of times a virtual page was not found in memory. If this number is consistently above 0, it indicates that too much memory has been allocated to an application, and not enough to Microsoft® Windows® 2000 Professional, or to the server you are running.
Server	Total Bytes/sec	Shows network activity. This gives you an idea of how close the Web server’s network adapter(s) are to being fully utilized. This is particularly useful on “multihomed” Web servers (which have a network adapter for each LAN they connect to).
Process	Private Bytes\ Inetinfo	The current number of bytes the HTTP/ASP service has allocated that cannot be shared with other processes. If this number is consistently large and growing, there is probably a leak in a Server-Side Object. Compare with Process\ Private Bytes: _Total.

Table 5.17 Useful Counters for Monitoring SQL Server Performance During Stress Testing

Object	Counter	Purpose/Description
SQLServer	Cache Hit Ratio	Shows the hit rate that data is found in the cache. If data is not in the cache, the server will have to be read from the disk. This shows memory allocation and therefore indicates whether the server has sufficient memory for the task. A number consistently less than 85 percent indicates a memory problem.
SQLServer	User Connections	Shows the number of active SQL users. Each connection uses 37 KB of memory. Compare this number to the Active Server Pages:Requests/sec counter to get an idea of how much the scripts are really working the SQL server. A large difference may indicate that the test script is not a valid stress of SQL server.
SQLServer	Net—Network Reads/sec	Shows the number of data packets read from the network. An extremely high value for an extended time indicates that either the network card has a problem, or more likely, the application is not using enough stored procedures and is written improperly.
SQLServer	I/O—Lazy Writes/sec	The number of flushed pages per second by the lazy writer. A number consistently above 0 indicates that the lazy writer is constantly working to flush buffers to disk. This means that the application either has a memory leak or the SQL Server requires more memory for normal operation.
SQLServer - Locks	Total Blocking Locks	Shows a lock that forces another process to wait until the current process is complete. An occasional block is normal. If this number is consistently greater than 0 it indicates transaction problems. Some of the basic causes are inefficient query design, poor table design, or slow throughput due to inadequate hardware.
PhysicalDisk	Disk Queue Length	Shows the number of outstanding requests on the disk. Sustained queue lengths on one disk that are greater than 3 indicate a disk or memory problem. It may also indicate that a SQL Server is not set up correctly.

Table 5.18 Useful Counters for Monitoring Performance of Both SQL and Web Servers During Stress Testing

Object	Counter	Purpose/Description
Processor	% Total Processor Time	Shows the amount of time spent processing threads by all CPUs. A number consistently above 85 percent on one or more processors indicates that the test is too intense for the hardware. Make sure you add the 0 through x instances of this counter for multiprocessor machines.
PhysicalDisk	% Disk Time	Requires “diskperf -y” at the command prompt. Shows the percentage of elapsed time that the disk is busy with read/write activity. A number consistently above 80 percent may indicate a memory leak. Make sure you add the 0 through x instances of this counter for multidisk machines.
Memory	Available Bytes	Shows the total bytes of real memory available to the computer, less the number of bytes being used by running applications. Add this number to Memory\ Committed Bytes to get the total amount of memory on the machine.
Memory	Pool Nonpaged Bytes	Shows pages that are used by the operating system that do not leave memory. This will increase with each process, but watch for gradual growth in this counter over a test run. This would indicate an application’s repeated inadvertent opening of a file or some other object. Performance will suffer if this approaches within 4 MB of Memory\ Available Bytes.
Memory	Pages/sec	Shows how many pages are being moved to and from the disk to satisfy virtual memory requirements. If the server does not have enough memory to handle its workload, this number will be consistently high.
Memory	Committed Bytes	Shows the size of virtual memory that has been committed to the running applications. Add this number to Memory\ Available Bytes in order to compute the total amount of memory on the machine. Committed bytes should increase as the test is ramping up, but it should remain fairly constant after that.
System	Total Interrupts/sec	Shows the frequency with which this computer is handling hardware interrupts. This gives you a good idea of how busy the whole system is.
Object	Threads	Threads are the basic executable entity that can execute instructions in a processor. If this number continues to rise over time, open the Computername\ Process\ Thread Count counter to discover which instance is creating all of the threads.
Process	Private Bytes: _Total	Shows the current number of bytes that all instances have allocated that cannot be shared with other processes. Make sure you select the _Total instance from the list, in addition to any other instances you suspect may be consuming too much memory.

See the following: