How does restic load indexes into memory

I was looking into how restic stores indexes in the cache and I came across Hashed array trees. But I was wondering if we can load into bolt a DB on disc like it was done in the posts linked below and will it actually make any difference. I have linked some reference documents on what I was reading through.
PS. It would be helpful if anyone can provide a brief or links to discussions that provide insight on how indexes are stored in memory.

I found these links rather helpful while looking into this:

I’m not actually sure which answer you’re looking for as you’ve already discovered the Hashed array tree. Although the latter is just an implementation detail of the index. In general, the index uses a HashMap<restic.ID, indexEntry> that’s optimized to reduce the memory overhead.

Replacing it with some other index implementation might be possible, however, that will probably have a significant performance impact. Access to the index is essentially random, which is the worst case for a disk based data structure.