How to understand why the large size of the table?

Question

PostgreSQL

Hello.
In psql I do \dt+ and there I see one table with a size: 746 MB
Next, I create a dump of this database:

pg_dump --username=user --format=custom --file=db.backup

I roll it on a clean database: pg_restore -d db_name_new db.backup --no-owner
I look at the new database \dt+ and there the size of this table is already there: 77 MB
At the same time, the number of records is the same
. What could be the reasons for such differences? Where to look?

Answer 1

the volume occupied by the table is not only valuable fur, but also 30-40 megabytes (and sometimes more) of space not freed after deleting records.
discover vacuum full, pgcompactor and other anti-bloating tools (not to be confused with bullying).