Essentially, yes. It’s the method I use (although I am not constrained by Pi performance). But go back a step and think about what you want - do you really want ‘every single Item’? Or every single change? Say you are polling a temperature sensor or suchlike, that will almost always be the last thing to have changed.
I have very few rules that just update the “log” Item though - the stuff I am interested in is usually being dealt with in some rule already - doors being opened, switches switched etc. So the line to update the log just fits into an existing rule, and I have it say something meaningful rather than just note a change.
I’m logging events of interest, not temp change from 17.1 to 17.2
This is quite a common request, a typical solution here
That does have limitations and will not work well here I think (multiple triggers).
If you really want a global last item changed, It should I think be possible to write an external script that parses out the last line of openhab.log, examines it see if it was an Item change, and returns it. I do not know how to go about that.