25.4.2 Memory Conservation Tips

Some tips to saving memory (some of these use examples from the cmcast-100.tcl script): If you have many links or nodes:

Avoid trace-all :

$ns trace-all $f causes trace objects to be pushed on all links. If you only want to trace one link, there's no need for this overhead. Saving is about 14 KB/link.

Use arrays for sequences of variables :

Each variable, say n$i in set n$i [$ns node], has a certain overhead. If a sequence of nodes are created as an array, i.e. n($i), then only one variable is created, consuming much less memory. Saving is about 40+ Byte/variable.

Avoid unnecessary variables :

If an object will not be referred to later on, avoid naming the object. E.g. set cmcast(1) [new CtrMcast $ns $n(1) $ctrmcastcomp [list 1 1]] would be better if replaced by new CtrMcast $ns $n(1) $ctrmcastcomp [list 1 1]. Saving is about 80 Byte/variable.

Run on top of FreeBSD :

malloc() overhead on FreeBSD is less than on some other systems. We will eventually port that allocator to other platofrms.

Dynamic binding :

Using bind() in C++ consumes memory for each object you create. This approach can be very expensive if you create many identical objects. Changing bind() to delay_bind() changes this memory requirement to per-class. See ns/object.cc for an example of how to do binding, either way.

Disabling packet headers :

For packet-intensive simulations, disabling all packet headers that you will not use in your simulation may significantly reduce memory usage. See Section  for detail.