How postgresql handles full table delete in terms of loading the full table in these scenarios
consider one big table(tablename: bigtable)
and the query will be >> delete from bigtable;
1)which doesn't have any foreign table reference with any other tables
2)And when this table is referenced by other table
You should at least consider whether you can use TRUNCATE, especially in #1
An actual delete has to modify every page for the table so it can mark every row as having been deleted. I don't think it needs to load TOAST data but am uncertain. I reasonably confident all non-TOASTED data will end up in buffers.
References would depend on CASCADE behavior but in a restrict mode only FK resolution triggers will be involved. In most well-design scenarios indexes are then used instead of the corresponding triggers. So less data but still likely every row will be read in.