Change function and Discard Unchanged

[TheBonaZabbix]

Dear all,
How does the CHANGE function (in a trigger) behave with an item on
which the Discard Unchanged is configured ?

I read the manual and I searched a bit on the forum but I could not find an answer.

The manual says
change: The amount of difference between last and previous values.

But what exactly is meant by previous value detected ?

For example....
These are item collection ranges (configured with Discarded Unchanged)

TIME	1	2	3	4	5
VALUES	0	NULL	NULL	NULL	1

(NULL = Discarded value)


In this case how will the trigger behave ?
Will it make 1-0 (where 1 is the last value obtained and 0 is the value obtained previously at time 1) ?
Will it make 1-NULL (where 1 is the last value obtained and NULL is the previous value -discarded- at time 4)

and if the trigger will execute 1-NULL what result will it return ?
1 or error (because it is not a valid mathematical operation) and then the trigger will never start ?


I hope I was clear enough.
Thanks in advance
AB

[Hamardaban]

"change" is "History function" that is, it works with data written to the database.
"Discarded Unchanged" discards data and does not write it to the database.
Has everything become clearer? :-)

[TheBonaZabbix]

Thanks for the answer Hamardaban!

Then the Change function will work correctly because it will read the last value written in the DB (even if, in the meantime, X values have been discarded)

Thank you very much.
Have a good day
AB