Postgres, why is pg_dumpall faster than pg_dump?

Question

PostgreSQL

Usually I did a dump using pg_dump, it took about 25 minutes.
I decided to make a dump using pg_dumpall, it took about 7 minutes.
Why such a difference?

Answer 1

https://www.postgresql.org/docs/9.2/app-pg-dumpall.html
pg_dumpall calls pg_dump in a loop, so there's no way it can be faster. You just have a measurement error: due to locks, caching, etc.