transction_timestamp() inside of procedures

This function shows that only clock_timestamp() advances inside a
procedure, not statement_timestamp() or transaction_timestamp():

CREATE OR REPLACE PROCEDURE test_timestamp () AS $$
DECLARE
str TEXT;
BEGIN
WHILE TRUE LOOP
-- clock_timestamp() is updated on every loop
SELECT clock_timestamp() INTO str;
RAISE NOTICE 'clock %', str;
SELECT statement_timestamp() INTO str;
RAISE NOTICE 'statement %', str;
SELECT transaction_timestamp() INTO str;
RAISE NOTICE 'transaction %', str;
COMMIT;

PERFORM pg_sleep(2);
END LOOP;
END
$$ LANGUAGE plpgsql;

CALL test_timestamp();
NOTICE: clock 2018-09-20 19:38:22.575794-04
NOTICE: statement 2018-09-20 19:38:22.575685-04
NOTICE: transaction 2018-09-20 19:38:22.575685-04

--> NOTICE: clock 2018-09-20 19:38:24.578027-04
NOTICE: statement 2018-09-20 19:38:22.575685-04
NOTICE: transaction 2018-09-20 19:38:22.575685-04

This surprised me since I expected a new timestamp after commit. Is
this something we want to change or document? Are there other
per-transaction behaviors we should adjust?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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