Java overhead Post: 302487182

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Top Forums Web Development Java overhead Post 302487182 by DGPickett on Tuesday 11th of January 2011 03:56:56 PM

01-11-2011

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Well, you can control JAVA behaviors with -X and other command line arguments, for instance to set the heap size -Xmx very high and to specify how much GC cost you want. GC is forced when the heap fills, and the heap is VM, disk is cheap, newer JAVA has nice GC, parallel and heuristic. These options also can turn on parrallel buffered I/O, resulting in fewer real reads and writes, faster with lower overhead, no code but one option.

Using a "Server" grade platform and server mode java means the code is more optimized.

Using 64 bit mode unnecessarily may add some overhead.

RAM is VM, so "RAM in use" is a useless concept. If a program using 20M of RAM exits, there is 20M free until there are 20M new page faults -- so what? Do you have too much paging?

CPU use is pretty much dependent on economical programming, finesse and real load. Finding out what code is the CPU hog is a big industry, easier in C/C++ than JAVA, as a short truss/tusc/strace of a JAVA process does not tell you much. Creation and destruction of complex objects frequently is a great cost, in JAVA or C++, and worse in JAVA since it forces more GC. Sometimes jobs running continuously can be run at intervals and in sequence, not in parallel, so they do not start the machine thrashing or peak the CPU usage.

DGPickett

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dacs.java

DACS.JAVA(7)						  DACS Miscellaneous Information					      DACS.JAVA(7)

NAME

       dacs.java - DACS Java support

DESCRIPTION

       This document describes support for Java provided by DACS.

       To enable Java support, DACS must be configured using the --enable-java flag. It may also be necessary to specify the location of the Java
       commands and include files. See dacs.install(7)[1].

	   Note
	   Java support is currently very limited and should be considered experimental. It is currently only possible to call dacsauth(1)[2] and
	   dacscheck(1)[3] using the Java Native Interface (JNI) provided. The command line arguments to both of these commands are exactly as
	   documented in their manual pages. Each argument is passed as a String.

	   The code is not thread-safe and is probably not suitable for being called many times within a particular process due to assumptions it
	   makes about dynamic memory allocation.

	   There are no immediate plans to improve or extend Java support. Using the existing capability to build the JNI layer, however, it
	   should not be difficult for an experienced Java programmer to build upon the example Java code provided.

       With Java support enabled, building DACS will copy the JNI shared library and a .jar file to the library directory (default:
       /usr/local/dacs/lib), and the JNI include files to the include directory (default: /usr/local/dacs/include).

       The tools/java/jni distribution directory contains a simple script called javarun that demonstrates how to run dacsauth or dacscheck as a
       Java application. For example, to validate the Unix password for user somebody, run (as root):

	   ./javarun dacsauth -m unix suff -user somebody -prompt

DIAGNOSTICS

       The return codes are as documented in the command's manual page.

AUTHOR

       Distributed Systems Software (www.dss.ca[4])

COPYING

       Copyright2003-2012 Distributed Systems Software. See the LICENSE[5] file that accompanies the distribution for licensing information.

NOTES

	1. dacs.install(7)
	   http://dacs.dss.ca/man/dacs.install.7.html

	2. dacsauth(1)
	   http://dacs.dss.ca/man/dacsauth.1.html

	3. dacscheck(1)
	   http://dacs.dss.ca/man/dacscheck.1.html

	4. www.dss.ca
	   http://www.dss.ca

	5. LICENSE
	   http://dacs.dss.ca/man/../misc/LICENSE

DACS 1.4.27b							    10/22/2012							      DACS.JAVA(7)