Proposal: knowing detail of config files via SQL

Hi,

As per discussion
<http://www.postgresql.org/message-id/CAD21AoDkds8Oqbr199wwrCp7fiDvOw6bbb+CGdwQHUF+gX_bVg@mail.gmail.com>,
I would like to proposal new view like pg_file_settings to know detail
of config file via SQL.

- Background
In 9.4 postgresql.auto.conf is added to support ALTER SYSTEM command
and that config file is loaded after whenever postgresql.conf is
loaded.
That is, postgresql.auto.conf is quite high priority so that the value
in postgresql.conf can not work at all if DBA set it manually.
ALTER SYSTEM RESET command can remove the unnecessary value in
postgresql.auto.conf but there are no way to know about where the
value has came from.
(They can only give the information about the setting in last file it
is present.)

- Solution
The patch not is implemented yet, just proposing now.
I'm imaging that we can have new pg_file_settings view has following
column to store current assigned value in config file.
- guc value name
- guc value
- config file path (e.g. /opt/data/postgresql.sql,
/opt/data/postgresql.auto.conf, /opt/hoge.conf)
This view could be convenient for DBA to decide if the
postgresql.auto.conf is useful or not and if it's not useful then DBA
could use ALTER SYSTEM .. RESET command to remove the same from
postgresql.auto.conf.

Also other idea is to add additional columns existing view
(pg_settings), according to prev discussion.

Please give me comments.

Regards,

-------
Sawada Masahiko