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Readme $Id: $ GCViewer 1.31 ============= GCViewer is a little tool that visualizes verbose GC output generated by Sun, IBM, HP and BEA Java Virtual Machines. It is free software released under GNU LGPL. You can start GCViewer by simply double-clicking on gcviewer-1.3x.jar or running java -jar gcviewer-1.3x.jar Supported verbose:gc formats are: - Sun JDK 1.6 with option -Xloggc:<file> [-XX:+PrintGCDetails] [-XX:+PrintGCDateStamps] - Sun JDK 1.4/1.5 with the option -Xloggc:<file> [-XX:+PrintGCDetails] - Sun JDK 1.2.2/1.3.1/1.4 with the option -verbose:gc - IBM JDK 1.3.1/1.3.0/1.2.2 with the option -verbose:gc - IBM iSeries Classic JVM 1.4.2 with option -verbose:gc - HP-UX JDK 1.2/1.3/1.4.x with the option -Xverbosegc - BEA JRockit 1.4.2/1.5 with the option -verbose:memory Best results are achieved with: -Xloggc:<file> -XX:+PrintGCDetails -XX:+PrintGCDateStamps Hendrik Schreiber wrote GCViewer up to 1.29. What you are seeing here is based on his very good work. In detail descriptions of most JVM parameters relevant to garbage collection can be found at http://www.tagtraum.com/gcviewer-vmflags.html GCViewer shows a number of lines etc. in a chart (first tab). These are: - Full GC Lines: o Black vertical line at every Full GC - Inc GC Lines: o Cyan vertical line at every Incremental GC - GC Times Line: o Green line that shows the length of all GCs - GC Times Rectangles: o Dark grey rectangle at every Full GC o Light grey rectangle at every Incremental GC o Grey rectangle at every 'normal' GC - Total Heap: o Red line that shows heap size - Tenured Generation: o Magenta area that shows the size of the tenured generation (not available without PrintGCDetails) - Young Generation: o Orange area that shows the size of the young generation (not available without PrintGCDetails) - Used Heap: o Blue line that shows used heap size - Initial mark level: o Yellow line that shows the heap usage at "initial-mark" event (only available when the gc algorithm uses concurrent collections, which is the case for CMS and G1) - Concurrent collections o Cyan vertical line for every begin (concurrent-mark-start) and pink vertical line for every end (CMS-concurrent-reset / G1: concurrent-cleanup-end) of a concurrent collection cycle In the second tab ("Event details") it shows details about the events it parsed: E.g. events like the following 24.187: [GC 24.188: [ParNew: 93184K->5464K(104832K), 0.0442895 secs] \ 93184K->5464K(1036928K), 0.0447149 secs] \ [Times: user=0.39 sys=0.07, real=0.05 secs] are shown in one line as GC ParNew: <number of events parsed>, <min duration>, <max duration>... Events like these 4183.962: [Full GC 4183.962: [CMS: 32957K->40326K(932096K), 2.3313389 secs] \ 76067K->40326K(1036928K), [CMS Perm : 43837K->43453K(43880K)], 2.3339606 secs] \ [Times: user=2.33 sys=0.01, real=2.33 secs] are shown as Full GC CMS: CMS Perm : <number of events parsed> ... So for every line the text is extracted (not always every part of it). This allows a user which is familiar with the text log files to find out more details about the events that occurred. Metrics ======= GCViewer provides some metrics to help you interpret the graph. Note that some metrics based on averages are shown along with their standard deviation. If it is obvious that the standard deviation is fairly big in comparison to the average, the values are grayed out, indicating that actual values are much smaller or bigger than the average. Summary ------- - Footprint: o Maximal amount of memory allocated - Freed Memory: o Total amount of memory that has been freed - Freed Mem/Min: o Amount of memory that has been freed per minute - Total Time: o Time data was collected for (only Sun 1.5/1.4/1.2.2 and IBM 1.3.1/1.3.0/1.2.2) - Acc Pauses: o Sum of all pauses due to GC - Throughput: o Time percentage the application was NOT busy with GC - Full GC Performance: o Performance of full collections. Note that all collections that include a collection of the tenured generation or are marked with "Full GC" are considered Full GC. - GC Performance: o Performance of minor collections. These are collections that are not full according to the definition above. Memory ------ - Total heap (usage / alloc max): o Max memory usage / allocation in total heap (the last is the same as "footprint" in Summary) - Tenured heap (usage / alloc max): o Max memory usage / allocation in tenured space - Young heap (usage / alloc max): o Max memory usage / allocation in young space - Perm heap (usage / alloc max): o Max memory usage / allocation in perm space - Avg after full GC: o The average heap memory consumption after a full collection - Avg after GC: o The average heap memory consumption after a minor collection - Freed Memory: o Total amount of memory that has been freed - Freed by full GC: o Amount of memory that has been freed by full collections - Freed by GC: o Amount of memory that has been freed by minor collections - Avg freed full GC: o Average amount of memory that has been freed by full collections - Avg freed GC: o Average amount of memory that has been freed by minor collections - Avg rel inc after FGC: o Average relative increase in memory consumption between full collections. This is the average difference between the memory consumption after a full collection to the memory consumption after the next full collection. - Avg rel inc after GC: o Average relative increase in memory consumption between minor collections. This is the average difference between the memory consumption after a minor collection to the memory consumption after the next minor collection. This can be used as an indicator for the amount of memory that survives minor collections and has to be moved to the survivor spaces or the tenured generation. This value added to "Avg freed GC" gives you an idea about the size of the young generation in case you don't have PrintGCDetails turned on. - Slope full GC: o Slope of the regression line for the memory consumption after full collections. This can be used as an indicator for the increase in indispensable memory consumption (base footprint) of an application over time. - Slope GC: o Average of the slope of the regression lines for the memory consumption after minor collections in between full collections. That is, if you have two full collections and many minor collections in between, GCViewer will calculate the slope for the minor collections up to the first full collection, then the slope of the minor collections between the first and the second full collection. Then it will compute a weighted average (each slope wil be weighted with the number of measuring points it was computed with). - initiatingOccFraction (avg / max) o CMS GC kicks in before tenured generation is filled. InitiatingOccupancyFraction tells you the avg / max usage in % of the tenured generation, when CMS GC started (initial mark). This value can be set manually using -XX:CMSInitiatingOccupancyFraction=<value>. - avg promotion o Promotion means the size of objects that are promoted from young to tenured generation during a young generation collection. Avg promotion shows the average amount of memory that is promoted from young to tenured with each young collection (only available with PrintGCDetails) - total promotion o Total promotion shows the total amount of memory that is promoted from young to tenured with all young collections in a file (only available with PrintGCDetails) Pause ----- - Acc Pauses: o Sum of all pauses due to any kind of GC - Number of Pauses: o Count of all pauses due to any kind of GC - Avg Pause: o Average length of a GC pause of any kind - Min / max Pause: o Shortest /longest pause of any kind - Avg pause interval: o avg interval between two pauses of any kind - Min / max pause interval: o Min / max interval between two pauses of any kind - Acc full GC: o Sum of all pauses due to full collections - Number of full GC pauses: o Count of all pauses due to full collections - Acc GC: o Sum of all full GC pauses - Avg full GC: o Average length of a full GC pause - Min / max full GC pause: o Shortest / longest full GC pause - Acc GC: o Sum of all pauses due to minor collections - Number of GC pauses: o Count of all pauses due to minor collections - Avg GC: o Average length of a minor collection pause - Min / max GC pause: o Shortest / longest minor GC pause Notes ===== This is not a perfect tool. However, GCViewer can help you getting a grip on finding out what's going on in your application with regards to garbage collection. Here are some known limitations. IBM JDKs -------- If you have problems with the IBM format, please check that every line of information is really in one line and not wrapped. The IBM format actually provides a lot more information than is visualized. Sun JDK 1.3.1/1.4 with -verbose:gc ---------------------------------- Sun JDK 1.3.1/1.4 with -verbose:gc does not provide a timestamp. Therefore values like 'Total Time', 'Throughput', and 'Freed Mem/Min' cannot be calculated. Sun JDK 1.5 (a.k.a. Java 5) --------------------------- -XX:+UseConcMarkSweepGC: The concurrently collected garbage is not correctly reflected in the data panel. Sun JDK 1.6 (a.k.a. Java 6) --------------------------- CMS and G1 collector sometimes mix concurrent events with stop the world collections in the output. In a few cases the parser can recover from such mixed lines, sometimes it can't and will show an error message. BEA JRockit 1.4.2/1.5 --------------------- Concurrently collected garbage may not be reflected correctly in the data panel. Export formats -------------- The CSV format is quite useful for importing the data to a spreadsheet application. However, it does not export all data. Internationalization -------------------- Provided are a German, an English and a Swedish localStrings.properties file. If someone feels the need to translate these to another language, please do so. I will be more than glad, to include it in a future version of this tool. Start of log / absolute times ----------------------------- If you happen to know when the application and GC log was started, you can specify this time by right-clicking on the time ruler and entering a start time. Sun VMs: IF -XX:+PrintGCDateStamps was used, the proposed start time is read from the gc log file. Bug reports ----------- If you are a developer, you may fork (http://help.github.com/fork-a-repo/) the repository on http://github.com/chewiebug/GCViewer and send me a pull request (http://help.github.com/send-pull-requests/). If you plan a bigger change I'd appreciate a notice in advance. To file a bug report, please open an issue on http://github.com/chewiebug/GCViewer/issues or send an email to email@example.com with a description of the error, the name of the JVM that produced the GC data and all used flags along with a sample GC log file. Building GCViewer from Source ----------------------------- Download and install Maven3 from http://maven.apache.org/ Download the src distribution of GCViewer. Execute from the GCViewer base directory (same as pom.xml): mvn clean install The executable jar will be placed in the target directory. Enjoy! Joerg Wuethrich http://github.com/chewiebug/GCViewer firstname.lastname@example.org