How to get a real time within PostgreSQL transaction?

问题

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?

回答1:

Timeofday()

May work for you.

回答2:

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.

回答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=#

来源：https://stackoverflow.com/questions/3363376/how-to-get-a-real-time-within-postgresql-transaction

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sql

database

postgresql

transactions