I'm learning about column orientated databases. I have just watched a YouTube video on column orientated databases by Arnaldo from MIT, who suggests an interesting motivation for column orientated databases. About half way through he talks about how long it takes to do a table scan for a query, and discusses the actual physical disk head reading from a spinning magnetic disk. He says that even though we may only want to query, say, 3 columns from a table with 100 columns, the disk head still needs to physically pass over the entire records in a row-orientated database, hence one reason why a column orientated storage system may be faster in some scenarios for querying.
I have a couple of questions about this:
How true is this, given that data in records may not actually be physically next to each other on disk (because of B+Tree index structures)? Is this an oversimplification, or is it true in some situations and not in others (e.g. in tables with no indexes)?
How does this relate to SSDs - as there is no spinning disk and head scanning over it, does the same principle hold true when data is stored in an SSD?