ABSOLUTE
is for counters which get reset upon reading. This is used
for fast counters which tend to overflow. So instead of
reading them normally you reset them after every read to
make sure you have a maximum time available before the next
overflow. Another usage is for things you count like number
of messages since the last update.


COUNTER
is for continuous incrementing counters like the ifInOctets
counter in a router. The COUNTER data source assumes that
the counter never decreases, except when a counter overr‐
flows. The update function takes the overflow into
account. The counter is stored as a per-second rate. When
the counter overflows, RRDtool checks if the overflow happ‐
pened at the 32bit or 64bit border and acts accordingly by
adding an appropriate value to the result.