Why are batch inserts/updates faster? How do batch updates work?

Question

Why are batch inserts faster? Is it because the connection and setup overhead for inserting a single row is the same for a set of rows? What other factors make batch inserts

Answer 1

I was looking for an answer on the same subject, about "bulk/batch" update. People often describe the problem by comparing it with insert clause with multiple value sets (the "bulk" part).

INSERT INTO mytable (mykey, mytext, myint)
VALUES 
  (1, 'text1', 11),
  (2, 'text2', 22),
  ...

Clear answer was still avoiding me, but I found the solution here: http://www.postgresql.org/docs/9.1/static/sql-values.html

To make it clear:

UPDATE mytable
SET 
  mytext = myvalues.mytext,
  myint = myvalues.myint
FROM (
  VALUES
    (1, 'textA', 99),
    (2, 'textB', 88),
    ...
) AS myvalues (mykey, mytext, myint)
WHERE mytable.mykey = myvalues.mykey

It has the same property of being "bulk" aka containing alot of data with one statement.