Using PLA.dll to collect perf counters

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Who doesn’t love diagnostics?! I am a big proponent of efficient and well thought out tracing and performance counters. They are invaluable for debugging, performance testing, health monitoring, and many other tasks worthy of future blog posts.

Seasoned Windows professionals are generally familiar with the Windows Resource and Performance Monitor tool. Slightly more advanced users are typically aware of the logman.exe tool which allows access to data collectors and performance logs via the command line. But in my experience, only a select few know about PLA.dll, the programmatic interface to performance logs and alerts on Windows.

As it turns out, due to strong COM interop support in .NET and the simplicity of adding COM reference assemblies in Visual Studio, it is a breeze to take advantage of PLA in your C# apps. Just go to your project, open the “Add Reference…” dialog, select “Browse…”, locate “pla.dll” (ships with Windows, typically in the %systemroot%\system32 folder), add it, and you’re ready to go.

Since PLA.dll is a COM library and geared mostly towards C++ developers, it is tricky to get the hang of using it in managed app. This is why I like to wrap it in a simpler, .NET-friendly fa├žade when I’m exposing it to larger applications. (Pro tip: using the protocol documentation for MS-PLA can fill in some details left out by the MSDN documentation.)

Here is a sample wrapper that shows one way to expose performance counter collection via data collector sets. All of this code is available on the PlaSample project in GitHub.

We start with a type representing a counter name:

public class CounterName
{
    public CounterName()
    {
    }

    public string Machine { get; set; }
        
    public string Category { get; set; }

    public string Counter { get; set; }

    public string Instance { get; set; }

    public override string ToString()
    {
        // . . .
    }
}

Now we abstract the data collector set into a CounterCollectorInfo:

public class CounterCollectorInfo
{
    public CounterCollectorInfo(string name)
    {
        this.Name = name;
        this.CounterNames = new List<CounterName>();
    }

    public string Name { get; private set; }

    public string OutputPath { get; set; }

    public TimeSpan? SampleInterval { get; set; }

    public LogFileFormat? LogFileFormat { get; set; }

    public IList<CounterName> CounterNames { get; private set; }
}

The LogFileFormat enum is mirror of the underlying PLA enum describing, predictably, the format of a perf counter log file:

public enum LogFileFormat
{
    CommaSeparated = 0,
    TabSeparated = 1,
    Sql = 2,
    Binary = 3,
}

Now for the nitty-gritty of interacting with PLA — code to create the data collector set for logging perf counters:

public ICollectorSet Create()
{
    // Data collector set is the core abstraction for collecting diagnostic data.
    DataCollectorSet dcs = new DataCollectorSet();

    // Set base folder to place output files.
    dcs.RootPath = this.OutputPath;

    // Create a data collector for perf counters.
    IPerformanceCounterDataCollector dc = (IPerformanceCounterDataCollector)dcs.DataCollectors.CreateDataCollector(DataCollectorType.plaPerformanceCounter);
    dc.name = this.Name + "_DC";
    dcs.DataCollectors.Add(dc);

    // Set output file name to use a pattern, as described at
    // http://msdn.microsoft.com/en-us/library/windows/desktop/aa372131(v=vs.85).aspx .
    dc.FileName = this.Name;
    dc.FileNameFormat = AutoPathFormat.plaPattern;
    dc.FileNameFormatPattern = @"\-yyyyMMdd\-HHmmss";

    // Set sample interval, if present.
    if (this.SampleInterval.HasValue)
    {
        dc.SampleInterval = (uint)this.SampleInterval.Value.TotalSeconds;
    }

    // Set log file format, if present.
    if (this.LogFileFormat.HasValue)
    {
        dc.LogFileFormat = (FileFormat)this.LogFileFormat.Value;
    }

    // Build up the list of performance counters.
    string[] counterNames = new string[this.CounterNames.Count];
    for (int i = 0; i < this.CounterNames.Count; ++i)
    {
        counterNames[i] = this.CounterNames[i].ToString();
    }

    dc.PerformanceCounters = counterNames;

    // Now actually create (or modify existing) the set.
    dcs.Commit(this.Name, null, CommitMode.plaCreateOrModify);

    // Return an opaque wrapper with which the user can control the session.
    return new CollectorSetWrapper(dcs);
}

The interface ICollectorSet provides a simple non-PLA-dependent API for interacting with the data collector set:

public interface ICollectorSet : ISessionController
{
    void Delete();
}

public interface ISessionController
{
    void Start();

    void Stop();
}

Finally, pulling it all together, a sample application to create a basic counter set and output a CSV file. Note that manipulating data collector sets requires special privileges. The simplest way to avoid “access denied” errors is to just run any PLA app elevated.

CounterCollectorInfo info = new CounterCollectorInfo("MyCounters");

info.SampleInterval = TimeSpan.FromSeconds(1.0d);
info.LogFileFormat = LogFileFormat.CommaSeparated;
info.OutputPath = Environment.CurrentDirectory;

info.CounterNames.Add(new CounterName() { Category = "Process", Counter = "Thread Count", Instance = "explorer" });
info.CounterNames.Add(new CounterName() { Category = "System", Counter = "System Calls/sec" });
info.CounterNames.Add(new CounterName() { Category = "Processor", Counter = "Interrupts/sec", Instance = "_Total" });

ICollectorSet collector = info.Create();
collector.Start();

Thread.Sleep(5000);

collector.Stop();

collector.Delete();

Run the program and you’ll get an output CSV file named “MyCounters-” followed by a timestamp. The contents will look something like this:
"(PDH-CSV 4.0) (Pacific Standard Time)(480)","\\Your-PC-Name\Process(explorer)\Thread Count","\\Your-PC-Name\System\System Calls/sec","\\Your-PC-Name\Processor(_Total)\Interrupts/sec"
"12/27/2013 12:24:33.231","39","46015.248698065603","3062.4673653801251"
. . .

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