NonStop Server for Java Programmer's Reference (NSJ 4.2+)

JVM Tuning Tools

PrintGCStats is a tool for mining verbose:gc logs that can aid analyzing and tuning garbage collection. You can

download this tool from the following location:

http://java.sun.com/developer/technicalArticles/Programming/turbo/PrintGCStats.zip

Additionally, for a discussion of profiling tools, see the Application Profiling section.

Tuning Application Performance

The topics are

Memory Considerations: Moving QIO to KSEG2●

Determining the Heap Manager●

Determining the Heap Setting●

Related Tuning Guides●

Memory Considerations: Moving QIO to KSEG2

Java server-side applications are typically configured with large Java heap sizes, in excess of 128 MB. In addition,

the JVM and its native components (for example, NonStop Servlets for JavaServer Pages (NSJSP) transport

library, JDBC Driver for SQL/MP, JDBC Driver for SQL/MX, SQL/MX call-level interface, and potentially any

custom-user JNI code) allocate memory for their own use. Thus, the overall heap space required by a JVM process

can be considerably higher than the configured Java heap space.

When a process uses the parallel TCP/IP transport provider for socket operations (like the iTP Secure WebServer

httpd daemon Server process instance), the process becomes a QIO client. For NonStop" Server QIO

shared-memory segments, when a QIO client process makes a socket request, a portion of the process address

space is reserved for the QIO segment. This reserved space limits the maximum useable heap size for the JVM

process.

The size of the QIO segment is determined by the configured physical memory for a processor (CPU) on the

NonStop system. For a processor on a NonStop system configured with 4 GB of physical memory, 512 MB are

used for the QIO segment. In addition, 512 MB of the user address space are reserved for the QIO segment, if the

process is also a QIO client.

To overcome the problem of losing address space to QIO, you can configure the QIO segment so that the segment

is moved to a special region of the privileged address space, called the KSEG2 region. Moving the QIO segment to

the KSEG2 region means that the maximum size of the QIO segment is restricted to 128 MB (instead of the default

512 MB). Before moving QIO to KSEG2, check that the current maximum QIO segment size in use is within the

128 MB limit (allowing for future requirements that may increase the QIO segment size). If the maximum QIO

segment size is within the limit, you can move QIO to KSEG2.

Example: Determining the QIO Segment Size in Use

To determine the QIO segment size in use, use the following SCF command from the TACL prompt:

TACL> scf

SCF - T9082G02 - (30APR03) (01APR03) - 03/19/2004 02:20:31 System \NAVAE1

(Invoking \NAVAE1.$DATA11.RAMR.SCFCSTM)