Identifying you memory shortages with Solaris
Pretty much all Unix sysadmins have been there: how do you identify whether your system is suffering from memory shortages?multiple scenarios exist: systems with little filesystem I/O or systems with lots of filesystem I/O.
1st we need to understand how the Solaris memory system works.
The Solaris memory system counts paging activity generated by both file I/O and application paging with the same counters.
Thus it becomes more difficult to observe the paging activity via the vmstat tool as a method of identifying those memory shortages.
but we can still use vmstat to take away the question of a memory shortage in some situations though.
- use vmstat to see if your system is showing paging activity. if it's not, there is no chance of a memory shortage.
- always look at your swap device for activity. if applications are paging then there must be significant I/O queuing going on for the swap device, hinting you of memory shortage.
the Solaris paging counters show us insight how busy the VM system is.
check the scan rate (the number of pages per second the pageout scanner is scanning).
a zero scan rate means no memory shortage.
Systems with lots of filesystem I/O
i'd like to concentrate on these types of systems since lots of file I/O is pretty common behavior on most servers.
due to the high levels of filesystem I/O it becomes much more difficult to ascertain if the box suffers from memory shortages thus resulting in excessive paging behavior and high scan rate numbers.
when memory shortage does occur, the majority of the page faults will incur I/O to the swap device.
using vmstat, check the swap device, pageout(po) and scan rate(sr) columns.
this little explanation merely touches the very surface of the Solaris memory system.
please, do read the excellent pdf 'The Solaris Memory System' available at Sun.com
posted by .marco. @ 21:00
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