If you want to get started with PDA, but don’t have any data at hand, don’t worry! PDA can generate some data for you to play with.
Before we can load data into PDA, we need some. PDA comes with a small demo which generates a CSV-based logfile, as well as a Java Garbage Collection logfile. Please run:
./writeJavaGC.sh
Click on Configure Project to configure the current (unnamed) project.
Now we want to add some files to this project. Click on the file open symbol and select the Garbage Collection logfile javagc.log that was just generated. A window Select Parser appears. PDA automatically tries to determine which parser it thinks can handle this file. If not already preselected, please chose HotSpot (de.nmichael.pda.parser.HotSpot) as the parser. In the table below, each parser provides some information on the data it can handle. Click OK to open and parse the file.
All data provided by parsers is organized in categories and subcategories, which contain one or multiple series. It is very much up to the parser, how data is organized. The Hotspot parser organizes its series into the cateogies gc for garbage collection related statistics, heap for heap usage and time for time spent in the application and the JVM. Subcategories for gc are the various garbage collection algorithms like ParNew, ParOld, CMS and G1, while for heap the subcategories are the various heap regions like Young, Eden, Survivor, Old, and Perm. Under these subcategories, you can then find the various series.
To add a series, click the Select Series button. For plotting our GC output, type heap into the field Filter to only filter for heap-related series. Now select the three series gc:heap:total:capacity, gc:heap:total:used and gc:heap:young:used by selecting them on the left side and clicking the right-arrow button to add them as selected series. Then click OK. PDA will now add all these series to the project, and automatically chose colors, styles and value ranges to plot them.
To change some attributes, now click on the Settings button of series gc:heap:young:used (which is the current Young Heap occupancy). For test purposes, change the maximum value of the Y axis (Range Y to) to 2.0E11 (that’s 200000000000.0), and change the parameter Value Axis to logarithmic. Click OK.
Now in the Configure Project dialog, enter a Title (for example, GC Demo), and click OK to plot the data.
All data plotted by PDA is value-time-based. All samples are aligned along a common time axis (X axis). Each series of data may have an individual scale on the value axis (Y axis). On the top of the screen, each series’ name can be found in the color used to plot that series. Underneath the name, you can see the value range. For example, series gc:heap:young:heap that we have edited before is plotted in green, using a value range from 0 to 200G on the Y axis.
Now click the Select Series button on the right, add series gc:gc:parnew:pause, and click OK.
Note also that different styles are used for the data. Most series are plotted using lines. Only series gc:gc:parnew:pause (the pause times for garbage collections in the young generation) are plotted using dots.
On the right side of the screen, click the button with the magenta label gc:gc:parnew:pause. A window named Series Statistics will pop up and display some statistics about this series, as the number of found samples within the selected time frame, Min/Max/Avg/Variance/Standard Deviation for this series, as well as the Min/Max/Avg distance between samples. In terms of garbage collection times, the Avg Distance is our average garbage collection interval, and the Avg Value is the average time (in this case in milliseconds) for a garbage collection. Click OK to close the window again.
With the mouse, you can zoom into data more closely, by selecting a certain part of the graph. Note that zooming will only zoom in on the X axis, not the Y axis. For example, zoom into the letter V of the plotted data. Now click the statistics button for series gc:gc:parnew:pause again and note that now the statistics only reflect the samples from the selected interval. After closing the statistics window, click the Reset Zoom button to reset the zoom.
By clicking Add Label, you can add a label to the graph and drag it to a position you like.
Click on Configure Project again to add more data, the click the file open symbol and select the demo.csv file that was generated earlier. Select parser csv (de.nmichael.pda.parser.Csv) and click OK to open and parse the data. Then click on Select Series, filter by csv, and add the csv:::Samples series. Click OK. Now click Settings for the just added series and change the Line Width to 10. Click OK, and OK again in the Configure Project dialog to plot the data.
The cyan line from the CSV parser shows the curve that the demo was trying to plot by triggering garbage collections at the appropriate point in time. In shape, it should match the GC output. To better align it with the rest of the data, click on the small configuration icon next to the Samples series in the graph window. This is a shortcut to change the properties of a series without going though Configure Project. Change Range Y8 to to 1.5E8 and click OK.
Now the curves align nicely. Often it is a useful thing to do to align various curve on a base point and look at their relative behavior and scaling from there on.
To save the project, select Save as... from the Project menu and save the project. It can then later be opened again.
To save the current graph as a PNG image, click the Save Image button or select Save As Image... from the Project menu.
Congratulations! Now you know how to use PDA.