Fix to allow pmlogger to log derived metrics. Logic lifted from libpcp
to preprocess and postprocess pmFetch calls and grafted into pmlogger's
myFetch routine.
In the archive, the derived metric is logged just like a real metric,
so name in the pmns, pmid as allocated by pmRegisterDerived, pmDesc
from expression tree and values from the the pmResult rewriting using
the expression tree.
derived metrics & pmlogger - fix
Fix to allow pmlogger to log derived metrics. Logic lifted from libpcp
to preprocess and postprocess pmFetch calls and grafted into pmlogger's
myFetch routine.
In the archive, the derived metric is logged just like a real metric,
so name in the pmns, pmid as allocated by pmRegisterDerived, pmDesc
from expression tree and values from the the pmResult rewriting using
the expression tree.