Hi,
Tom Lane <tgl@sss.pgh.pa.us> writes:
> "Scott Whitney" <swhitney@journyx.com> writes:
>> I _thought_ I had seen such behavior in the past, but I've never found (not
>> particularly looked) for such information. Top seems to lie to me on a
>> fairly-regular basis, and not just via PG...
>
> This particular effect only applies to applications that use large
> chunks of shared memory. There might be some other misleading things
> :-(
You might appreciate this reading (which talks about using exmap to get
reliable figures, but it seems to relate to shared objects and it's
unclear whether exmap will account correctly for IPC shared memory):
http://ktown.kde.org/~seli/memory/desktop_benchmark.html
The tool used to measure memory usage was Exmap - the only tool for
measuring memory usage that I've ever found to be actually useful (I
think I've already blogged about it ;) ). Its so-called effective
memory usage numbers try to account for things like dividing shared
libraries among all the processes using them, unlike tools like top
that just report the numbers they find in /proc and nobody really
knows how to interpret them. In other words, if you use things like
top or free for precise measuring of memory usage, you're
crazy. Nevertheless, for the crazy ones, I used also free alongside
with Exmap, just for the fun of it, numbers from free will follow in
parentheses. They should not be considered to be useful though.
Regards,
--
dim
