hi Alan,
On Jul 13, 9:00pm, Alan Bailey wrote:
> Subject: why not install as DSO?
> I've got a simple question. Why is the default to install pmdas as
> daemons instead of as a DSO? I quote from pmdaproc.sh:
>
> # Install control variables
> # Can install as DSO?
> dso_opt=false
>
> I kinda like installing them as DSO's because it puts everything into one
> process. It might also end up taking up less memory. Which one is
> recommended, and why? Or is this something that is figured out at install
> time, and since I'm on a linux system, it thinks it shouldn't install it
> as a DSO?
>
> Just wondering.
>
One thing to bear in mind is that pmcd is single threaded by
design, so a PMDA which takes some time to fetch new data can
cause pmcd to respond more slowly - eg. if the fetch mechanism
has to block while obtaining data. The kernel PMDAs (for both
IRIX + Linux) tend to use system calls to fetch their data and
are very lightweight - other PMDAs are not quite so cheap.
Another factor is that a separate process is self-contained,
so a crash in a non-DSO PMDA won't cause pmcd to die & pmcd
can continue on gracefully serving up other metrics in this
situation.
There is little difference between the Install scripts on
Linux and IRIX, so the choice of DSO/daemon usually defaults
to daemon (on all platforms) to try to improve parallelism
and robustness.
cheers.
--
Nathan
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