Memory Bottle necks: How do you find Physical memory issues? Physical memory related bottle necks?

Physical memory: In UNIX environment physical memory can be found by using VMSTAT command. Normally people thing if there is a paging indication, then there is a problem with physical memory, but in fact it is not. But you have to see the ‘Scan Rate’ metrics to find out the physical memory issue. Because this metric will tell you when ever the OS will scan for memory pages to page out.
Normally all OS will maintain the memory to cache the input/output pages to improve the performance by saving disk memory. Paging is only a problem when the memory used by the application/product is paged to the physical disc. But before this happens, you will normally look for page scanning activity by OS in the VMSTAT.