Add UUID examples. Page density exploration.

[andyatkinson]

Blog post

Avoid UUID Version 4 Primary Keys

UUID Experiments

PgPrewarm and Pageinspect

create extension if not exists pg_prewarm;
create extension if not exists pageinspect;

• Use UUID v7 extension to generate values on Postgres 16
  https://pgxn.org/dist/pg_uuidv7/
• enable pageinspect in target DB

I run Postgres 16 on macOS using Postgres.app.

cd # into pg_uuidv7 directory
make
sudo make install PG_CONFIG=/Applications/Postgres.app/Contents/Versions/16/bin/pg_config

Then from psql, in the target database:

create extension pg_uuidv7;

• Reproduce results here:
  https://www.cybertec-postgresql.com/en/unexpected-downsides-of-uuid-keys-in-postgresql/

For the page density comparison, see page_density.sql