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<h3><a name="jvmArgs">3.2 Java Flags</a></h3>
<p>In most cases it is not necessary to specify any additional
arguments to the Java runtime, but it can be useful in certain
circumstances. The two main kinds of options you might want to
specify directly to Java are these:
<dl>
<dt><strong>System properties</strong></dt>
<dd>System properties are a way of getting information into the
Java runtime from the outside, rather like environment variables.
There is a list of the ones which have significance to STILTS
in <a href="sysProperties.html">Section 3.3</a>. You can set them from the
command line using a flag of the form <code>-Dname=value</code>.
So for instance to ensure that temporary files are written to
the <code>/home/scratch</code> directory, you could use the flag
<pre>
-Djava.io.tmpdir=/home/scratch
</pre>
</dd>
<dt><strong>Memory size</strong></dt>
<dd>Java runs with a fixed amount of 'heap' memory; this is
typically 64Mb by default.
If one of the tools fails with a message that says it's out of memory
then this has proved too small for the job in hand. You can increase the
heap memory with the <code>-Xmx</code> flag. To set the heap
memory size to 256 megabytes, use the flag
<pre>
-Xmx256M
</pre>
(don't forget the 'M' for megabyte). You will probably find
performance is dreadful if you specify a heap size larger than
the physical memory of the machine you're running on.
</dd>
</dl>
</p>
<p>You can specify other options to Java such as tuning and profiling
flags etc, but if you want to do that sort of thing
you probably don't need me to tell you about it.
</p>
<p>If you are using the <code>stilts</code> command-line script,
any flags to it starting <code>-D</code> or <code>-X</code> are passed
directly to the <code>java</code> executable.
You can pass other flags to Java with the <code>stilts</code> script's
<code>-J</code> flag; for instance:
<pre>
stilts -Xmx4M -J-verbose:gc calc 'mjdToIso(0)'
</pre>
is equivalent to
<pre>
java -Xmx4M -verbose:gc -jar stilts.jar calc 'mjdToIso(0)'
</pre>
</p>
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<hr><i>STILTS - Starlink Tables Infrastructure Library Tool Set<br>Starlink User Note256<br>STILTS web page:
<a href="http://www.starlink.ac.uk/stilts/">http://www.starlink.ac.uk/stilts/</a><br>Author email:
<a href="mailto:m.b.taylor@bristol.ac.uk">m.b.taylor@bristol.ac.uk</a><br>Mailing list:
<a href="mailto:topcat-user@jiscmail.ac.uk">topcat-user@jiscmail.ac.uk</a><br></i></body>
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