[phiresky]

The B-Tree is a tree that in this case is perfectly balanced. So if you do a query with an index in a database it will fetch an logarithmic amount of data from the index and then a constant amount of data from the table.

For the example the wdi_data table is 300MB and an index on it is 100MB in size. This index has a tree depth of 4 - which means SQLite has to read exactly 4 pages (4KiB) to get to the bottom of it and find the exact position of the actual row data.

you can check the depth of the b-trees with `sqlite3_analyzer`.