Обсуждение: SET feature

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/15/sql-set.html
Description:

Hi,

I remember in version 9 , to use variable you had to change in the
postgresql. 

Today it is easier , just use

SET SESSION myprefix.myvariable =  'whatever' 

and all the transactions can use it , it is very useful in some cases, for
example to track the author of a change , you don't need to change all your
java/php/python code , just use a trigger on the table to fill up a column
"change_by"

I've checked the documentation and that feature is not explained at all, not
even in the SET Command.

Hope it  helps


Regards,

Sparkx

On Fri, 2022-10-28 at 10:14 +0000, PG Doc comments form wrote:
> I remember in version 9 , to use variable you had to change in the
> postgresql. 
> 
> Today it is easier , just use
> 
> SET SESSION myprefix.myvariable =  'whatever' 
> 
> and all the transactions can use it , it is very useful in some cases, for
> example to track the author of a change , you don't need to change all your
> java/php/python code , just use a trigger on the table to fill up a column
> "change_by"
> 
> I've checked the documentation and that feature is not explained at all, not
> even in the SET Command.

Most people consider this a kind of abuse of what is known as "placeholder parameters",
documented in https://www.postgresql.org/docs/current/runtime-config-custom.html

See for example https://postgr.es/m/2982579.1662416866%40sss.pgh.pa.us

I believe it is a deliberate choice not to advertise that as "session variables",
particularly since there is an improvement in the pipeline:

https://commitfest.postgresql.org/40/1608/

Yours,
Laurenz Albe