System Memory Allocation View

Function:

• To display system memory usage.

Description:

• This view displays a horizontal bar graph showing the system memory allocation.

• The user memory bar is the memory dedicated to user programs. The free memory bar indicates the amount of unallocated memory. The amount of free memory is an important statistic because of its impact on the system. The UNIX System paging and swapping policies are usually activated when free memory drops below a certain threshold (usually about 25% free). When this occurs, pages are stolen from processes and inactive programs are swapped out to disk. This increases free memory until there is sufficient memory to execute runnable programs. Thus the free memory statistic tends to oscillate within a range. The real test of whether there is sufficient memory is to look at the swapping/paging statistic in the System Bottleneck View. If there is significant swapping activity, you probably have insufficient memory.

• The Overview computes a memory load statistic that accounts for this nonlinear behavior and provides a percentage memory load factor by considering both the memory and swapping loads. This result will magnify the memory critical range and give a real indication of the impact any memory shortages are placing on the system. This statistic is drawn from the Percent Database's load table.

• The os_code bar represents the memory allocated for the operating system program itself, while os_data represents the internal operating system data. The operating system memory is fixed and not tunable.

• The buffer bar represents the memory dedicated to the system buffer cache. If there is a consistent excess of free memory, you may wish to consider increasing the system buffer cache to reduce any I/O load. The stream bar indicates memory allocated to streams buffers which are used primarily by networking devices and protocols.

• See your operating system manuals for instructions on how to reconfigure your operating system tunable parameters.