Re: Hardware upgrade for a high-traffic database

> > Hi Rod,
> >
> > I was looking at top and vmstat - which always show under 300MB
> "Active".
> > We may hit 400MB at peak. Everything I see (though this isn't my area
> of
> > expertise) points to most of the memory simply being unused. Results
> below,
> > am I missing something?
>
> This looks fine. The memory is not unused (only 5MB is actually empty)
> but is being used for disk cache.
>
> Active is memory used by programs and would need to be swapped if this
> space was needed.
>
> Inactive is memory that is generally dirty. Disk cache is often here. In
> your case, you likely write to the same pages you're reading from --
> which is why this number is so big. It also explains why a checkpoint is
> a killer; a large chunk of this memory set needs to be pushed to disk.
>
> Cache is memory used generally for disk cache that is not dirty. It's
> been read from the disk and could be cleared immediately if necessary.
>
> Wired is memory that cannot be swapped. In your case, Shared Memory is
> probably Wired (this is good). There is another sysctl to check and set
> whether it is wired or swappable.
>
>
>
> Interesting (if dry) read:
> http://www.freebsd.org/doc/en_US.ISO8859-1/articles/vm-design/index.html
>

Ah, thanks - I didn't know that Inactive was still being used. I'm glad to
know that at least the OS is using up the free memory for disk cache.
Shared memory is Wired, set via sysctl. Thanks for the info! It sounds
like adding more memory would help cache more data - I'll look into the
upgrade.

Jason