Question about user/database-level parameters

At Mon, 01 Aug 2022 18:24:33 +0800, Japin Li <japinli@hotmail.com> wrote in

Hi, hackers

When I try to modify the parameters for all users in the following command [1]
(the library doesn't exist), and I quit the connection, I cannot log in the
database, how can I bypass this checking?

I find those parameters loaded by process_settings(), and it seems no way to
disable this loading process. If we could bypass this checking, how can we
fix these parameters?

[1]
postgres=# ALTER ROLE all SET local_preload_libraries TO fdafd;
ALTER ROLE
postgres=# \q

$ psql postgres
psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: FATAL: could not access file "$libdir/plugins/fdafd": No such file or directory

Can you run the server in single-user mode? That mode doesn't try
loading libraries.

regareds.

--
Kyotaro Horiguchi
NTT Open Source Software Center

On Tue, 02 Aug 2022 at 13:01, Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote:

At Mon, 01 Aug 2022 18:24:33 +0800, Japin Li <japinli@hotmail.com> wrote in

Hi, hackers

When I try to modify the parameters for all users in the following command [1]
(the library doesn't exist), and I quit the connection, I cannot log in the
database, how can I bypass this checking?

I find those parameters loaded by process_settings(), and it seems no way to
disable this loading process. If we could bypass this checking, how can we
fix these parameters?

[1]
postgres=# ALTER ROLE all SET local_preload_libraries TO fdafd;
ALTER ROLE
postgres=# \q

$ psql postgres
psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: FATAL: could not access file "$libdir/plugins/fdafd": No such file or directory

Can you run the server in single-user mode? That mode doesn't try
loading libraries.

Yeah, the single-user mode works. Thank you very much!
However, if the database is in production, we cannot go into single-user mode,
should we provide an option to change this behavior on the fly?

--
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.

Japin Li <japinli@hotmail.com> writes:

Yeah, the single-user mode works. Thank you very much!
However, if the database is in production, we cannot go into single-user mode,
should we provide an option to change this behavior on the fly?

There is not, and never will be, a version of Postgres in which
it's impossible for a superuser to shoot himself in the foot.

Test your settings more carefully before applying them to a
production database that you can't afford to mess up.

regards, tom lane

On Tue, 02 Aug 2022 at 13:44, Tom Lane <tgl@sss.pgh.pa.us> wrote:

Japin Li <japinli@hotmail.com> writes:

Yeah, the single-user mode works. Thank you very much!
However, if the database is in production, we cannot go into single-user mode,
should we provide an option to change this behavior on the fly?

There is not, and never will be, a version of Postgres in which
it's impossible for a superuser to shoot himself in the foot.

Test your settings more carefully before applying them to a
production database that you can't afford to mess up.

Thanks for your explanation! Got it.

--
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.

Japin Li wrote:

However, if the database is in production, we cannot go into single-user
mode, should we provide an option to change this behavior on the fly?

It already exists, through PGOPTIONS, which appears to work
for local_preload_libraries, in a quick test.

That is, you can log in by invoking psql with:
PGOPTIONS="-c local_preload_libraries="
and issue the ALTER USER to reset things back to normal
without stopping the instance.

Best regards,
--
Daniel Vérité
https://postgresql.verite.pro/
Twitter: @DanielVerite

On Thu, 04 Aug 2022 at 19:29, Daniel Verite <daniel@manitou-mail.org> wrote:

Japin Li wrote:

However, if the database is in production, we cannot go into single-user
mode, should we provide an option to change this behavior on the fly?

It already exists, through PGOPTIONS, which appears to work
for local_preload_libraries, in a quick test.

That is, you can log in by invoking psql with:
PGOPTIONS="-c local_preload_libraries="
and issue the ALTER USER to reset things back to normal
without stopping the instance.

Oh, great! Thank you very much!

--
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.