Faster data load

Hi,

We are having a requirement to create approx 50 billion rows in a partition
table(~1 billion rows per partition, 200+gb size daily partitions) for a
performance test. We are currently using ' insert into <target
table_partition> select.. From <source_table_partition> or <some
transformed query>;' method . We have dropped all indexes and constraints
First and then doing the load. Still it's taking 2-3 hours to populate one
partition. Is there a faster way to achieve this?

Few teammate suggesting to use copy command and use file load instead,
which will be faster. So I wanted to understand, how different things it
does behind the scenes as compared to insert as select command? As because
it only deals with sql engine only.

Additionally, when we were trying to create indexes post data load on one
partition, it took 30+ minutes. Any possible way to make it faster?

Is there any way to drive the above things in parallel by utilizing full
database resources?

It's postgres 15.4

Regards
Lok