| Description | Sampling interval for objects in this expression with
expObjectSampleType 'deltaValue'.
This object is not instantiated if not applicable.
A value of 0 indicates no automated sampling. In this case
the delta is the difference from the last time the
expression was evaluated. Note that this is subject to
unpredictable delta times in the face of retries or
multiple managers.
A value greater than zero is the number of seconds between
automated samples.
Until the delta interval has expired once the delta for the
object is effectively not instantiated and evaluating
the expression has results as if the object itself were not
instantiated.
Note that delta values potentially consume large amounts of
system CPU and memory. Delta state and processing must
continue constantly even if the expression is not being
used. That is, the expression is being evaluated every
delta interval, even if no application is reading those
values. For wildcarded objects this can be substantial
overhead.
Note that delta intervals, external expression value
sampling intervals and delta intervals for expressions
within other expressions can have unusual interactions as
they are impossible to synchronize accurately. In general
one interval embedded below another must be enough shorter
that the higher sample sees relatively smooth, predictable
behavior. |