In some tables, I have serial to manage a unique identifier.
As an example I have a column calld id_data as a serial4.
I have in my tables 30 rows with id_data from 1 to 30
Then I delete rows with id 10 and 11.
Then I vaccum the table.
I create some new rows and the id_data starts with 10 then 11 and then 12. But the problem is that 12 already exists. So I have 2 rows with the same id_data.
Sorry if my problem is simple but I thought that the serial will keep moving starting at 31 instead of 10.