On Sun, 22 Feb 2004, Scott Phalen wrote:

> Thanks, Henrik! I have been watching my squid server all weekend and have
> noticed it hovers around 5-8MB of free RAM. I have a windows background and
> fairly new to the linux world. I saw no RAM as a bad thing. But everything
> seems to be working fine.


5-8MB sounds about right.

Output of "free" in the +/- buffers line is a relatively good figure to
read if you want to know how much memory is in use. If you want to read
the top output then this is the the sum of the Free + Cache + Buffers
fields.

Cache and Buffers are memory used by the OS to speed up disk I/O. It is
not entirely correct to say this is free memory as some is required for
disk I/O, but most will be reclaimed automatically should the system run
short of memory for the applications.

To determine if you have the correct amount of memory is a lot harder as
it is very hard to tell how much memory is required for Cache + Buffers
for good performance. The more disk I/O you have the more Cache + Buffers
is needed for best system performance. But if you see that the Cache +
Buffers is reasonable and that there is no swap activity then it can be
said that the amount of memory is sufficient, and if you see a lot of
Cache + Buffers then you have more than what is required.

For this reason the rule of thumb is to have 50% more physical ram than
required by Squid alone. This 50% gives the OS sufficient headroom for I/O
buffers etc, and works out quite well over the scale of different Squid
installations as the I/O intensity tends to increase with the size of the
Squid installation.

Regards
Henrik