Question

I need to write a plpgsql function which executes update statement in an infinite loop:

create function change_type() returns void as $$
begin
  loop  
    update table a set type = 1 where date < now(); 
  end loop;
end;
$$ LANGUAGE plpgsql;

When I call this function the update statement is not executed, although I can see that the loop is running. I ran the update statement as a single query and it works. How can I solve this problem?

Thanks

Answer 1

I guess what you are looking for is a cronjob to schedule a task at certain times (repeatedly). Try man crontab on a on UNIX / LINUX system. Preferably as system user postgres.

To run a query every 5 minutes, enter a line like this in your cron table. I use crontab -e under LINUX to edit my cron jobs:

* 5 * * * psql mydb -c 'UPDATE TABLE a SET type = 1 WHERE date < now()'

If you have more complex jobs, create a shell script with multiple SQL commands and call it like:

* 5 * * * psql mydb -f '/path/to/my_script.sh'

Or create a plpgsql function and call it:

* 5 * * * psql mydb -c 'SELECT myfunc()'

Set your system up so that the superuser postgres can log in without password (is default).

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Or have a look at pgAgent that is shipped with pgAdmin.