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

Answer 1

Timeofday()

May work for you.

Answer 2

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=# 

Answer 3

Use clock_timestamp().

now() is a traditional PostgreSQL equivalent to transaction_timestamp(), which is equivalent to CURRENT_TIMESTAMP. These functions return the start time of the current transaction. Their values do not change during the transaction.

statement_timestamp() returns the time of receipt of the latest command message from the client.

clock_timestamp() returns the actual current time, and therefore its value changes even within a single SQL command.

For more information see the documentation.