ALTER SESSION

Hello.

https://www.postgresql.org/message-id/20190128.133143.115303042.horiguchi.kyotaro@lab.ntt.co.jp

> C. Provide session-specific GUC variable (that overides the global one)
> - Add new configuration file "postgresql.conf.<PID>" and
> pg_reload_conf() let the session with the PID loads it as if
> it is the last included file. All such files are removed at
> startup or at the end of the coressponding session.
>
> - Add a new syntax like this:
> ALTER SESSION WITH (pid=xxxx)
> SET configuration_parameter {TO | =} {value | 'value' | DEFAULT}
> RESET configuration_parameter
> RESET ALL
>
> - Target variables are marked with GUC_REMOTE.
>
> I'll consider the last choice and will come up with a patch.

This is that, with a small change in design.

ALTER SESSION WITH (pid <pid>) SET param {TO|=} value [ IMMEDIATE ]
ALTER SESSION WITH (pid <pid>) RESET param [ IMMEDIATE ]
ALTER SESSION WITH (pid <pid>) RESET ALL

The first form create an entry in
$PGDATA/pg_session_conf/postgresql.<beid>.conf.
The second form removes the entry.
The third form removes the file itself.

IMMEDIATE specifies that the change is applied immediately by
sending SIGHUP to the process. pg_reload_conf() works as well.

The session configuration is removed at session-end and the
directory is cleaned up at startup.

It can change varaibles of PGC_USERSET by non-superuser or
PGC_SUSET by superuser. The local session user should have the
same privileges with pg_signal_backend() on the target session.

This patch contains documentation but doesn't contain test yet.

I would appreciate any comments or suggestions on this.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center