Nathan addressed most of the issues.
The one that I would add is that if you have a PMDA where you want to
fetch _just_ the metrics from that PMDA (possibly with some IRIX/Linux
metrics) _and_ you want a very fast sampling rate, then the DSO method
is the one of choice.
These pre-conditions are rare, so the default is to _not_ install as
a DSO.
Note that if you use the source of the existing PMDAs that link with
libpcp_pmda as the base for your new plug in, then the code will compile
to produce _both_ a DSO and a daemon PMDA ... this is not an accident
... the choice relates to a trade-off of run-time performance vs pmcd
robustness vs PMDA flexibility (there are things like sproc/pthread that
you'd have to be silly to use in a DSO PMDA).
Hope this helps.
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