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The -Xverbosegc option, available for the HP-UX
HotSpot™ VM, was specifically designed to produce ASCII garbage
collection data files for in-depth analysis using HPjmeter. -Xloggc can be useful for quick comparison
of garbage collection behavior across different platforms. Data Collection with -Xverbosegc | |
-Xverbosegc produces detailed
information about the performance of individual garbage collector
types for the entire Java application. To run your application with an option to capture
the garbage collection information, use the following command: $ java ... -Xverbosegc[0|1][:file=[stdout|stderr|filename[,[n][h][d][u][t]]]]
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The following table lists examples of supported -Xverbosegc options for capturing garbage collection data.
This table provides information for Java 1.5.0.04. Other versions
may differ from this. HPjmeter correctly presents and labels collected
data based on the Java version running with the application. To see
the complete list of available options for the Java version you are
running, use
$ java ... -Xverbosegc:help |
To see the availability of HPjmeter metrics from -Xverbosegc data collection, see –Xverbosegc and –Xloggc Options and Their Corresponding
Metrics. Table 6-1 Supported -Xverbosegc options for Java 1.5.0.04 | 0|1 | 0 prints
after every old generation garbage collection
or after a full GC 1 prints after every garbage
collection (default) | | :file=[stdout|stderr|filename] | stderr (default) directs output to
standard error stream stdout directs output
to standard output stream filename where the output shall be written | | [n[h[d[u[t]]]]] | where:n prevents appending the pid to the log filename h appends the hostname to the log
file name u appends the username to the log
file name d appends the date to the log file
name t appends the time to the log file
name
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At every selected garbage collection, the following
20 fields are printed. These values hold true for Java 1.5.0.04. Other
versions may differ. To see the complete list of available fields
for the Java version you are running, use java ... -Xverbosegc:help
Table 6-2 Fields Captured in GC Log Data When Using -Xverbosegc print options | %1 | Type of garbage collection. 1 = scavenge (of new generation only) 2 = old generation GC or full GC 3 = complete background, concurrent mark and sweep (CMS)
GC 4 = incomplete background, concurrent
mark and sweep GC 11 = Ongoing CMS
GC | | %2 | This value varies
depending on the value of %1.When %1 is
equal to 1, %2 indicates
whether or not a parallel scavenge occurred. Possible values are: n(>0): parallel scavenge
with n number of parallel GC threads
When %1 is equal to 2, %2 indicates that an old
generation GC or full GC has occurred. Reasons for the GC are given
as: 1: Allocation failure, followed
by a failed scavenge, leading to a full GC 2: Call to System.gc made 3: Tenured generation is full 4: Permanent generation is full 5: Scavenge followed by a train
collection 6: Concurrent-Mark-Sweep (CMS)
generation is full 7: Old generation expanded on last
scavenge 8: Old generation too full to scavenge 10: Allocation profiler triggered 11: JVMTI-forced garbage collection 13: Last ditch collection 14: GC Locker-Initiated GC 15: Heap Dump Triggered GC (HP
implementation) 16: Heap Dump Triggered GC
When %1 is equal to 3, %2 indicates that a complete
background, concurrent mark and sweep GC has occurred. Reasons for
the GC are given as: 1: Occupancy > initiating occupancy 3: Incremental collection will
fail 4: Linear allocation will fail
When %1 is equal to 4, %2 indicates that an incomplete
background, concurrent mark and sweep GC has occurred as a result
of exiting after yielding to foreground GC. The form for this data
set is given as n.m where n is the GC reason as follows: 1: Occupancy > initiating occupancy 3: Incremental collection will
fail 4: Linear allocation will fail 6: Incremental CMS garbage collection
and m indicates the background CMS
state when yielding, as follows: 7. Abortable pre-cleaning
When %1 is equal to 11, %2 indicates the stop-the-world
phase of CMS GC, as follows: 2: Initial marking (first stop-the-world
phase) 4: Final marking (second stop–the-world
phase)
| | %3 | Program time at the
beginning of the collection, in seconds | | %4 | Garbage collection
invocation. Counts of background CMS garbage collections and other
garbage collections are maintained separately | | %5 | Size of the object
allocation request that forced the GC, in bytes | | %6 | Tenuring threshold
- memory allocation that determines how long newborn objects remain
in the new generation, in bytes. These spaces are reported:Occupied before garbage collection (Before) Occupied after garbage collection (After) Current capacity (Capacity)
| | %7, %8, %9 | Eden sub-space
within the new generation, in bytes. These spaces are reported: | | %10, %11,%12 | Survivor
sub-space within the new generation, in bytes. These spaces are reported: | | %13, %14, %15 | Old generation,
in bytes. These spaces are reported: | | %16, %17, %18 | Permanent
generation, in bytes. These spaces are reported for storage of reflective
objects: | | %19 | Total stop-the-world
duration, in seconds. | | %20 | Total time used in
collection, in seconds. |
Collecting Allocation Site Statistics for Viewing in HPjmeterUse the following command to capture allocation site statistics
in a file for display in the HPjmeter garbage collection viewer. The
GC viewer automatically opens when you open a verbosegc or loggc file
from the HPjmeter console. $ java ... -XX:+PrintAllocStatistics -Xverbosegc[0|1][:file=[filename[,[n][h][d][u][t]]]]
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Data from the opened file is visible in the “Allocation Site Statistics” visualizer. Data Collection with -Xloggc | |
-Xloggc directs a smaller set
of data to a file than what is available with -Xverbosegc. For every garbage collection, the following six
fields are printed to the log file: Cumulative time since data collection began (in seconds) Heap in use before the GC event Heap in use after the GC event Current maximum heap size
To capture basic -Xloggc data,
use the following command: $ java ... -Xloggc:filename |
More data are available if you start the
JVM with the -XX:+PrintGCDetails or -XX:+PrintHeapAtGC options. For example, you can type: $ java ... -XX:+PrintGCDetails -Xloggc:filename |
Use these additional options
to obtain more data on GC activity in the eden space, the survivor
space, the old generation, and the permanent generation. To see the availability in HPjmeter of metrics derived from -Xloggc data, see –Xverbosegc and –Xloggc Options and Their Corresponding
Metrics. Naming GC Data Files | |
The following table shows the file name formats
used by default when naming files containing garbage collection data.
You may want to follow this convention when naming GC data files,
but it is not required.
Table 6-3 Default File Name Suffixes for GC Data | Option | File Name
Suffix |
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| -Xverbosegc | .vgc | | -Xloggc | .vgc |
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