Charting server load

[Zbigniew Koziol]

On Thursday 01 February 2007 15:18, Lennart Sorensen wrote:
> On Fri, Feb 02, 2007 at 01:21:30PM +1859, Ian Petersen wrote:
>
> The load is simply: On average how many processes are in the 'ready to
> run' state.  If on average, 0.5 processes are ready to run, then you can
> only be using 50% cpu, while if 3 processes are, then you must be
> running at 100% cpu, unless you have more than 3 processors.

Not quite true.

In case of Linux, it is not only the number of processes that counts but also 
the number of attempts to read or write to a file (writing in particular is 
time consuming).

Hence, CPU might be using 5% of its ability, RAM might be used in 10% only, 
while load might go to 50 and the computer will slow down tremendously when 
for instance a heavy usage of database takes place. Adding CPU or RAM will... 
surprise, surprise! will NOT help! The system spends simply too much time in 
a state when attempts to get to hard drive are done.

I observed that situation when experimenting with postgres. Solution which is 
used in similar cases is... putting postgres data to RAM instead on HD.

zb.

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