I fully agree that the actual impact of a large cache is “hard to say”.
Since the question of this thread was about not having “adverse effects” it makes an answer hard, as it is very hard from the outside to truly understand … which wall the sim is running into … at what point … and why.
However, one upper limit is very easy to calculate with high certainty. You can find the details of my argument in this post:
The core observation was this:
- The index area of the RC has a fixed size (512 MB)
- Each entry in the index has a fixed size (72 byte)
From that I concluded that …
- Sizes above 250 GB might be a waste of storage,
- … as the sim might not be able to use it all (due to the nature of the RC index structure).
A little later …
I was able to calculate a size distribution of the blob items of the cache. And …
- I did (again) see an average blob item size of around 30 KB.
If I combine that then we are looking at this:
- A cache index which can hold a maximum of 7,456,540 items
- … with around 30 kB per cached blob item data
- … means a likely maximum useable blob area of 214 GB
So any RC size above 214 GB is very likely a pure waste of local storage capacity.
Combined with the RC problems resulting from a "RC index full dump” logic I concluded back in January:
Regarding the RC size we find ourselves between “a rock and a hard place”.
- 16 GB is too small (= big LRU problem) … but at least it keeps the index small.
- 256 GB “solves” the LRU problem … but the large index will cause “stutters”.
I started to repeat some of the tests with SU3 and I am still not sure if there are any fundamental changes to the RC subsystem and the way in which the rendering pipeline interacts with it.
So in short … sadly … I am still not sure how to give a really good answer to the question which @BearsAreCool510 raised in this thread.