[hobbit] Memory check

[Stef Coene]

On Wednesday 08 February 2006 08:34, Rolf Schrittenlocher wrote:
> We are working with Solaris 9 and for them unfortunately there is no
> ACTUAL MEMory presented. But PHYSical MEMory is always high on some
> machines runing a database in warm standby for the same reasons as
> Henrik explained. In other words: The way it is this test is useless for
> us. I'd prefer other columns of vmstat checked as io, etc. Did anyone
> work in this direction or where have I to dig in trying these changes?
Swap is usage is _not_ important.  Most systems are a) using all available 
memory for disk cache, b) swapping not recently used programs to swap in 
favour for disk cache and c) doing prea-llocation of swap space (reserving 
disk cache even when it's not yet needed).
So, memory usage is 100% and swap usage can be high even if you have enough 
memory and not using any swap.

What you have to monitor is a) swap-in / swap-out and b) free list (I know 
this exist for AIX, but I don't know for other os's).
-> The swap-in / swap-out statistics determine how much of swap is activly 
used by the system as memory (in best scenario this is most of the time 0 or 
at least sometimes 0).
-> The free list determines how much memory is free and can be used for 
programs who really need it very fast (in best scenario this never turns 0).

There are other numbers that are important like page scans and stuff, but 
page-in and page-out are the most important.

That's why I mailed some days ago to this list to add extra graphs to the 
memory overview page.  The answer was that this will be not so easy to 
implement.


Stef