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SQL Server 2012 : Performance Monitor Overview (part 5) - Remotely Running PerfMon

1/4/2015 8:48:03 PM
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Remotely Running PerfMon

Like many server management tools, an instance of PerfMon can be connected to a remote server for remote monitoring. This avoids the need to connect via Remote Desktop and may reduce the overhead of monitoring on the target server.

To run PerfMon against a remote server, when adding counters, specify the target server name, replacing <Local computer> in the “Select counters from computer” drop-down box (see Figure 7). In order to use PerfMon remotely, you’ll need to be a Local Administrator on the target server, and the remote registry service should be running.



Factors to Consider When Running PerfMon

Monitoring servers adds overhead but it can be necessary. All data capture tools impose some cost to the target server. Our challenge is to resolve an incident (often performance related) while minimizing the overhead. When monitoring, you should consider performance implications with a view to reducing overhead and minimizing two main risks:

  • Making problems worse
  • Affecting data capture

PerfMon counters are themselves updated by the application, even when not consumed by PerfMon. Therefore, any performance overhead with PerfMon is only usually encountered when polling (or sampling) these counters and when writing these to disk if a collector has been set up.

The overhead of using PerfMon to monitor normal servers with regular workload is typically minimal. Performance becomes a discussion point when monitoring servers operating in time-sensitive environments (e.g., trading or reservation platforms) or with servers suffering acute performance problems — those in which the monitoring overhead could tip the server over the edge.

Because reading PerfMon counters is the only real overhead of concern, you should consider network time and disk activity during monitoring. If you can perceive performance degradation when running PerfMon, you can quickly and easily stop logging and measure any performance improvement.

NOTE One of the challenges with many performance problems is that you must obtain a PerfMon log to identify the cause of the problem. Without a log, engineers and managers can observe poor application performance and hypothesize about potential causes and remedies, but performance data is needed in order to diagnose the problem and take remedial action.
Frequently, you just have to accept the risk and overhead of running PerfMon because there simply is no better way to obtain performance data that will help solve a problem.

The Impact of Running PerfMon

PerfMon is a lightweight tool and its impact on any given server is partly related to how PerfMon is configured, but it is also dependent on the workload of that server while PerfMon is running. To illustrate this scenario, consider two servers: Server A is suffering under heavy workload with 99% CPU utilization and poor disk performance, while server B currently runs with 20% CPU and good disk response times. In this case, it’s likely that the impact to server A is greater because PerfMon could consume 1% or 2% available CPU capacity, whereas that same amount added by PerfMon to server B will have negligible detectable impact.

Many organizations attempt to reduce the risk and impact to systems by monitoring during periods of low activity — e.g., during lunch or late afternoon — when user volumes and activity are typically lower, but this is usually the worst idea! It is essential to capture data while the problem is happening, not on either side of the problem (typically when concurrency is at its peak). Additionally, the worse the problem, the easier it is to spot. Often problems are accentuated with user activity, so if they’re more likely to occur and be worse when they do happen, you’ve got the best chance possible to capture a log containing them.

There are three key factors to consider when determining the impact of PerfMon: sample interval, number of counters, and disk performance. The following sections take a brief look at each.

Sample Interval

The sample interval controls the frequency with which PerfMon polls counters to read their values. The more often PerfMon samples, the greater the impact to the server and the more log data generated. The default is 15 seconds, which is usually fine when tracing for a few hours only; when tracing over longer periods, reducing the sample interval reduces both the overhead of PerfMon and the size of the file generated.

Consider a situation in which you have a busy system with a high workload but very short transactions — sampling every 60 seconds could miss many of these very short transactions. The sample interval can affect the shape of the data, so always be aware of it and the overall monitoring window when reviewing performance logs, especially when looking at min, max, and average values. Take into account system activity and usage patterns to ensure that the log is representative of typical workload.

Number of Counters

A consideration with similar impact to sample interval, more counters results in a higher cost to sample and store those counter values. Most instance counters have a _TOTAL counter, which is a total of the individual counter instances combined. In some cases, such as for disk counters, this total is of limited use, as usually the details about each disk (instance) counter are required to identify disk performance problems. The total can hide problems, because an average might look healthy; but a very busy disk could be masked by several other disks with little activity.

Disk Performance

When capturing performance data using Data Collector Sets, consider where the log files will be stored. The objective is to minimize the impact to SQL Server; log performance data to a file on disk (not a database); and, where available, use a disk that will not contend with any databases — i.e., avoid any disks where data or log files are stored.

PerfMon logs grow in a linear and predictable pattern (unlike SQL Profiler trace files, which are workload dependent); for example, sampling 100 counters every 15 seconds for 5 minutes might create a 2MB PerfMon log file, so it would be reasonable to estimate that logging 100 counters for six hours would generate a 144MB log file. Generally, I try to avoid capturing data to a system drive, as the implications of filling that drive are much greater than when logging to a nonsystem drive.

Servers Suffering Very Poor Performance

When capturing PerfMon logs on servers with acute performance problems, run PerfMon as cautiously as possible to reduce the impact while still harvesting performance data. Here are some guidelines:

  • Run PerfMon remotely.
  • Reduce the sampling interval.
  • Include as few counters as possible.
  • Log to disk.

Common PerfMon Problems

You may sometimes encounter problems with PerfMon itself — specifically, counters could be missing, they might not be displayed correctly, or there could be problems connecting to servers remotely. This section contains a brief summary of some common issues and how to resolve them.

Using PerfMon on 64-bit Systems Using WOW

When running x64 Windows with x86 SQL Server, you’re using Windows on Windows (WOW), which means x64 Windows is emulating an x86 environment to host x86 SQL Server. If you’re using x64 Windows and x64 SQL Server, this section isn’t relevant to you.

When PerfMon runs on an x64 host, none of the counters pertaining to x86 applications are available because the x64 PerfMon cannot load x86 counters. You can overcome this by launching the x86 version of the Microsoft Management Console (MMC) with the PerfMon snap-in. Run the following to launch the PerfMon x86 from an x64 Windows computer:

mmc /32 perfmon.msc

NOTE If you’re running SQL Server in a Windows on Windows (WOW) mode — i.e., x86 SQL Server on x64 Windows — you’ll be unable to run PerfMon remotely from other x64 machines because the remote Registry service is an x64 process; therefore, counters are visible only to x86 processes.

Remote Monitoring Fails

If you’re trying to monitor remote servers without any success, the most likely cause is permissions problems. Try the following troubleshooting tips:

  • Ensure that the account is local administrator on the target server.
  • Confirm NetBIOS access to the target server.
  • Ensure that the remote Registry service is running on the target server.
  • Ensure that no local security policy or Active Directory group policy is restricting access.

SQL Server Counters Are Missing

When you open PerfMon, you might find that there are no SQL Server counters available in the counter list. This problem occurs more often on clustered instances. If counters are missing, check the SQL Server Error Log and the Windows Event Application log to determine whether any errors are logged regarding the failed counters. If there are no errors in either log, you can unload the counters as follows:

unlodctr mssqlserver

Once the counters have been unloaded, verify the path to sqlctr.ini and use the following command to reload the counters:

lodctr C:\Program Files\Microsoft SQL Server\MSSQL10.1\MSSQL\Binn\sqlctr.ini

As with any change, test the process on a nonproduction server to gain confidence in the process (even if there is no problem on the test server, you can still test the commands). After reloading the counters, if they still aren’t listed, use the following process to rebuild them.

Counters Are Missing or Numbers Appear Instead of Names

If when you attempt to add performance counters the list contains numbers instead of counter names, the counters could have been corrupted by a process incorrectly modifying the Registry.

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