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
