in Pl/PgSQL, do commit every 5000 records

[Emi Lu <emilu@xxxxxxxxxxxxxxxxx>]

Good morning,

In a plpgsql function, I am trying to insert 900, 000 records into 
several tables. I remembered people mentioned before that it is better 
and more efficient to commit actions for let's say every 5000 records' 
insertion.

May I get more inputs about why and how this commit can speed up the 
transaction please?

Thanks a lot,
Ying