Re: [patch] GUC source file and line number]

Before I respond to Tom's comments, let me step back a second and add the 
intro the deadline didn't leave me time for.  There are two specific 
things the bit I added to this GUC patch is aimed at:

1) Somebody has a postgresql.conf from a random source (saw it on the 
Internet and pasted dubious stuff in/previous person working on the 
server/etc.) and wants to know the default value they'd get if they just 
commented a specific line or lines out.

2) A GUC tuning tool author wants to provide a UI for modifying a GUC 
parameter that shows the default as input to the person deciding what to 
set a parameter to.  The interface I've always wanted to make available 
would be...wait a minute, I can provide a working example now.  Picture 
this:
    name     | Recommended | Current |  Min  | Default |   Max
-------------+-------------+---------+-------+---------+--------- wal_buffers | 1024kB      | 64kB    | 32 kB | 64 kB
|2048 MB
 

With your cursor lighting up either the "Recommended" or "Current" field, 
depending on whether you're a default approve or deny kind of tool 
designer.  Pretty simple interface to decide what to do, right?  I find 
that much less useful without the default value being included, but right 
now someone who is writing a tuning tool has to maintain their own 
database with that information if they want to do that.  I will actually 
do that for earlier versions the minute I know what the 8.4 solution that 
makes the problem go away looks like.

The above is the output from:

select name,  '1024kB' as "Recommended",  current_setting(name) as "Current",  case when unit='8kB' then
pg_size_pretty(min_val::int8*8192)else
 
min_val end as "Min",  case when unit='8kB' then pg_size_pretty(default_val::int8*8192) else
default_val end as "Default",  case when unit='8kB' then pg_size_pretty(max_val::int8) else max_val end
as "Max"  from pg_settings where name='wal_buffers';

on my system with the patch installed.

That's what I wanted but was unable to get until now.  Combine that with 
being able to figure out what source file and line the setting was 
actually taken from, and the top 3 obstacles to writing a simple and easy 
to use read/modify/write tuning tool are all cleared.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD