Re: warn if GUC set to an invalid shared library - Mailing list pgsql-hackers

From Maciek Sakrejda
Subject Re: warn if GUC set to an invalid shared library
Date
Msg-id CAOtHd0BtAEQukewfXyWBtyDeiM5BvHPVCHu3dKaBmtrU8Z0=Hg@mail.gmail.com
Whole thread Raw
Responses Re: warn if GUC set to an invalid shared library
List pgsql-hackers
Thanks for working on this! I tried it out and it worked for me. I
reviewed the patch and didn't see any problems, but I'm not much of a
C programmer.

On Tue, Dec 28, 2021 at 9:45 AM Justin Pryzby <pryzby@telsasoft.com> wrote:
> 0002 adds context when failing to start.
>
>         2021-12-27 17:01:12.996 CST postmaster[1403] WARNING:  could not load library: $libdir/plugins/asdf: cannot
openshared object file: No such file or directory
 
>         2021-12-27 17:01:14.938 CST postmaster[1403] FATAL:  could not access file "asdf": No such file or directory
>         2021-12-27 17:01:14.938 CST postmaster[1403] CONTEXT:  guc "shared_preload_libraries"
>         2021-12-27 17:01:14.939 CST postmaster[1403] LOG:  database system is shut down

For whatever reason, I get slightly different (and somewhat redundant)
output on failing to start:

2022-01-08 12:59:36.784 PST [324482] WARNING:  could not load library:
$libdir/plugins/totally bogus: cannot open shared object file: No such
file or directory
2022-01-08 12:59:36.787 PST [324482] FATAL:  could not load library:
totally bogus: cannot open shared object file: No such file or
directory
2022-01-08 12:59:36.787 PST [324482] LOG:  database system is shut down

I'm on a pretty standard Ubuntu 20.04 (with PGDG packages installed
for 11, 12, and 13). I did configure to a --prefix and set
LD_LIBRARY_PATH and PATH. Not sure if this is an issue in my
environment or a platform difference?

Also, regarding the original warning:

2022-01-08 12:57:24.953 PST [324338] WARNING:  could not load library:
$libdir/plugins/totally bogus: cannot open shared object file: No such
file or directory

I think this is pretty clear to users familiar with
shared_preload_libraries. However, for someone less experienced with
Postgres and just following instructions on how to set up, e.g.,
auto_explain (and making a typo), it's not clear from this message
that your server will fail to start again after this if you shut it
down (or it crashes!), and how to get out of this situation. Should we
add a HINT to that effect?

Similarly, for

> 0001 adds WARNINGs when doing SET:
>
>         postgres=# SET local_preload_libraries=xyz;
>         WARNING:  could not load library: xyz: cannot open shared object file: No such file or directory
>         SET

This works for me, but should this explain the impact (especially if
used with something like ALTER ROLE)? I guess that's probably because
the context may not be easily accessible. I think
shared_preload_libraries is much more common, though, so I'm more
interested in a warning there.

Thanks,
Maciek



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