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Open a blg file in Windows

In some versions of Windows, the usual method of viewing a file–double clicking on it–doesn’t work for BLG files. If you can’t view a BLG file just by double clicking on it, here’s the other way to open a BLG file in Windows.

This works in current versions of Windows and all the way back to Windows 2000.

open a blg file in Windows

BLG is the Performance Monitor file format. Here’s how to open one if double-clicking doesn’t work.

BLG is the file format that Performance Monitor, sometimes called Perfmon, uses to save performance data. Most newer versions of Windows make it easy. Double-clicking on the BLG file makes it open, as you would expect any other filetype to work. But if it doesn’t work for some reason, or you’re working with a really old Windows box, here’s how to get the file open to you can view and analyze it.

Launch Performance Monitor to open a blg file

On really old versions of Windows like Windows 2000, Windows XP and Server 2003, go to Control Panel > Administrative Tools. Open Performance. On recent versions of Windows you can just click Start and start typing Performance, and pick Performance Monitor from the list when it comes up.

How to open a BLG file from inside Performance Monitor

The icon you want varies in position and appearance on the toolbar. It’s usually kind of square and it’s usually on the far left or the far right. Hover over each icon and look at the tooltips. You want the one that gives the tooltip of “View Log File Data.” Translated into the English you and I speak, that means, “Open a stinkin’ BLG file!” You can also try hitting CTRL-L. In recent versions of Windows, that keyboard shortcut works.

Click that icon. Then on the resulting dialog box, click the source tab, click the button labeled Add. Change the radio button to Log Files, and you’re on your way. Click OK, and Performance Monitor will render the data in the BLG file so you can work with it.

13 thoughts on “Open a blg file in Windows”

  1. Even though it doesn’t explain how to read the file type, is a good source of file-extension definitions (now that no longer exists).

    Repeat after me: “Microsoft Usability Lab” (howls of derisive laughter, Bruce :).

  2. For me, it’s the fourth icon from the left, not the right. So I click that and get a file explorer, click the file I want to open, and … and … and … it goes off without complaining and not opening any file.

  3. Hey Lewis, I had the same problem, until I saved the monitoring settings (.msc) from the original PC and loaded them on the PC I was using to read the log.

  4. If you opent the log file, and nothing seems to happen, it’s because you still have to specify what counters you want to view, by pressing the “+” icon.

  5. Thanks Dave! Like you I spent many a minute trying to find out how to read log BLG files, but thanks to you I now can! Cheers and be lucky!

  6. Thanks Dave, you spared me some time!
    PS, here’s the official way as specified in the MS helpfiles. (I prefer yours though!)

    To use logged data

    Open Performance.
    Right-click the System Monitor details pane and click Properties.
    Click the Source tab.
    Under Data Source, click Log File, and type the path to the file or click Browse to browse for the log file you want.
    Click Time Range. To specify the time range in the log file that you want to view, drag the bar or its handles for the appropriate starting and ending times.
    Click the Data tab and click Add to open the Add Counters dialog box. The counters you selected during log configuration are shown. You can include all or some of these in your graph.

    To open Performance, click Start, point to Programs, point to Administrative Tools, and then click Performance.
    Unless you specifically want to monitor start-up events, you should exclude times that include such events from your time window because these temporary high values tend to skew overall performance results.
    The button on the toolbar is disabled when you are viewing log data.
    You can also view counter-log data by opening files that have been saved in comma-separated or tab-separated format using Microsoft Excel.

  7. Answered my own question:

    Took advantage of WinXP relog.exe capabilites and transferred the file to a Winxp machine.

    1) Go to the cmd prompt and get to the folder containing the file you want to change and type:

    relog filname.blg -f CSV -o newfile.csv
    2) transfer the file back to your Win2000 machine

    Now you can view it in csv format.

  8. Glad I found your site, Google indexes it. Yes it was pretty confusing. First I found the disk icon, opened the file, then what? Wasn’t clear to me that I have to then add the performance counters into the graph..

    Thanks Microsoft, that’s very intuitive…

  9. Rediculous that through all the help files on how to create the damn files there is no details on how to read the things !!!!, I now need to find out how to read the .ETL files !!.

    Thanks for this info though.


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