As per this doc, it is mentioned that we should ensure the working set fits into the RAM.
Also, as per this doc, wiredTiger uses 50% of the RAM and the rest is utilized by the filesystem cache & other MongoDB processes.
My concern is, should we ensure that the RAM is sized such that the working set fits into the WiredTiger cache (50% of the RAM) or into memory (100% of RAM)?
I see that the wiredtiger cache holds data in uncompressed form, whereas the filesystem cache holds the data in the same form as on disk & only advantage being avoiding more expensive disk reads.
So, should we ensure the working set fits into WiredTiger cache for best performance??
For example, lets say we have 100GB (indexes) + 10 GB (working set), should we size the RAM to be ~120 GB or 240 GB??