How to get a real time within PostgreSQL transaction?

Question

As far as I understand now() returns the same time during the whole PostgreSQL transaction? But how to get real time?

Also, I am interested if there any configuration parameter to limit duration of transaction, so that after this period expiration transaction would immediately fail or somehow else prohibit following queries?

Answer 1

You can use CURRENT_TIMESTAMP.

Answer 2

Timeofday()

May work for you.

Answer 3

To limit the time of a statement (not a transaction) you can use statement_timeout. now() will increment on each execution if not within a transaction block. Thus:

postgres=# select now();
              now              
-------------------------------
 2010-08-11 13:44:36.207614-07
(1 row)

postgres=# select now();
              now              
-------------------------------
 2010-08-11 13:44:36.688054-07
(1 row)

postgres=# select now();
              now              
-------------------------------
 2010-08-11 13:44:40.407623-07
(1 row)

postgres=# begin;
BEGIN
postgres=# select now();
              now              
-------------------------------
 2010-08-11 13:44:43.417611-07
(1 row)

postgres=# select now();
              now              
-------------------------------
 2010-08-11 13:44:43.417611-07
(1 row)

postgres=#