This might be off topic for this group; if so please direct me to a
more
appropriate group.
I have 20 years of programming experience (hobby / personal scale)

What are the best books on relational database implementation, and by
this I do not mean how to design your database schema, but how to
write an actual database, what the on disk data structures would be
like, caching, how to implement transactions, etc.

I am learning about database systems, and I am reading a book called
"Physical Database Design".
It gets to a bit about a large sequential access (e.g. for a full
table scan), and does the following:

I have something like:
TABLE A
a PK
TABLE B