Backend & systems·Data modelling and storage engines
you pick the primary key and quietly decide the physical order the rows will be stored in on disk forever.
Clustered index
Also calledindex-organised table, primary key ordering
An index whose leaf level is the table itself, so row order on disk follows the key. Range scans on that key become sequential reads, which is enormous; everything else becomes a secondary lookup. Choosing a random UUID as the clustered key scatters inserts across the whole file and is a classic self-inflicted write bottleneck.