The main thing to learn about btrees is that they have very high branching to ensure shallowness and thus trade off more sequential accesses for fewer random accesses, a good tradeoff for disk I/O. The other thing is to recognise that sorted access is still better than random access even over an index; better for disk / block cache, better for CPU cache, and seemingly redundant sorts can e.g. have outsize constant factor performance wins for some joins over materialized subtable queries.

Is a btree with a million nodes really going to be any easier to understand? Like I understand some times its better to have more realistic data (e.g for presenting results related to benchmarking performance), but for a post explaining the data structures behind a database it wouldn't help at all.

yeah, I think it would ultimately give the reader better understanding of how a real SQL system works. The idea, after all, is to give the reader an understanding that they can use to go on and create performant applications, right? If you create an application while thinking of the database as a 2d table with single digit dimensions, you may make some pretty big design missteps when it scales to hold real data.

Hi, - thanks for the feedback - I appreciate it. Negative feedback is always helpful :)

I did originally try using a meatier example but I found that doing that a) makes writing the article really hard - for example, diagramming a meaningful database is a lot of work and makes the diagrams incomprehensive and b) it is that much harder to trasmit the principles than when the example is trivial.

Alternatively, analytics databases don't use indices by design, as for most queries they need to shuffle entire datasets anyways. For example, https://dbdb.io/db/vertica: "Indexes are not support in Vertica."

Indexes are part of the SQL standard, so they are certainly pertinent for "SQL database" discussion.

Plenty of analytical databases still use indexes; bitmap indexes, date ranges, "clustered" indexes and even ordered/btree indexes all still come in handy because they can all help whittle down queries from billions to millions of records.

They just need to be ready to do efficient full table scans.

IIRC Microsoft provided a full blown demo database ( either for SQL Server or from Access, I can't remember ).

Northwind Traders, IIRC