NonStop Server for Java 6.0 Programmer's Reference

You must use both M and N when you use the -XX:GCLogLimits=M,N option. If this option is
not specified, the default behavior is to write a single GC log file with unlimited size.
When rotation is in effect, a sequence number is appended to the GC filename (0 through N-1).
(Examples of file names are: filename.0, filename.1, and filename.2).
With log rotation, when the specified maximum number of files (N) is reached, logging cycles
back to the first file in the sequence (filename.0), thereby overwriting the old GC data with
new data. If the maximum number of files (N) is never reached, then no log rotation occurs.
Examples:
To rotate between two log files, each with a maximum of 100,000 GC records, use:
-XX:GCLogLimits=100000,2
To maintain an unlimited number of smaller files, each with a maximum of 1,000 GC records,
use:
-XX:GCLogLimits=1000,0
Oracle’s Implementation
From NSJ 6.0 SPR — T2766H60^ACH and later versions, Oracle command line options support
GC log file rotation. The options are as follows:
• —XX:+UseGCLogFileRotation —XX:NumberOfGCLogFiles=<num_of_files>
• —XX:GCLogFileSize=<logsize>
NOTE: —Xverbosegc supports the listed options.
HP’s GC log rotation option, —XX:GCLogLimits, remains unchanged and still supports both
—Xloggc and —Xverbosegc options.
NOTE: HP’s LogRotation option —XX:GCLogLimits=M,N overrides Javasoft’s LogRotation
options. If HP's —XX:GCLogLimits is specified, GC logs rotate to new log file after N records.
Analyzing Garbage Collection Data
After completing the data file collection, perform the following steps:
1. Transfer the data file to an HPjmeter console compatible platform (HP-UX, Windows, or Linux).
2. Run the HPjmeter console and open the data file.
NOTE:
• Starting with NonStop Java 6.0 T2766H60^ABP release, NonStop Java supports rotational
GC logging into multiple GC log files to help control the GC log file size. For information on
GC log rotation, see “GC Log Rotation” (page 78).
• For information on analyzing GC profile data , see the HPjmeter 4.2 User’s Guide available
at www.hp.com/go/hpjmeter.
• The instructions for using the HPjmeter tool on the NonStop platform are provided in “Addendum
to HPjmeter 4.2 User's Guide” (page 88).
-Xeprof versus -agentlib:hprof (HPROF)
Xeprof is a superior profiling tool compared to HPROF in terms of the richness of data. However,
Xeprof has a little higher performance impact on an application than HPROF. For a comparison
of the features of Xeprof and HPROF, before using either of the profiles, see Table 5-4 in the
HPjmeter 4.2 User’s Guide.
Analyzing Garbage Collection Data 79