Configuration include directory

Two years ago Magnus submitted a patch to parse all the configuration 
files in a directory.  After some discussion I tried to summarize what I 
thought the most popular ideas were for moving that forward:

http://archives.postgresql.org/pgsql-hackers/2009-10/msg01452.php
http://archives.postgresql.org/pgsql-hackers/2009-10/msg01631.php

And I've now cleared the bit rot and updated that patch to do what was 
discussed.  Main feature set:

-Called by specifying "includedir <directory>".  No changes to the 
shipped postgresql.conf yet.
-Takes an input directory name
-If it's not an absolute path, considers that relative to the -D option 
(if specified) or PGDATA, the same logic used to locate the 
postgresql.conf (unless a full path to it is used)
-Considers all names in that directory that end with *.conf  [Discussion 
concluded more flexibility here would be of limited value relative to 
how it complicates the implementation]
-Loops over the files found in sorted order by name

The idea here is that it will be easier to write tools that customize 
the database configuration if they can just write a new file out, rather 
than needing to parse the whole configuration file first.  This would 
allow Apache style configuration directories.  My end goal here is to 
see all of the work initdb does pushed into a new file included by this 
scheme.  People could then expect a functionally empty postgresql.conf 
except for an includedir, and the customization would go into 00initdb.  
Getting some agreement on that is not necessary for this feature to go 
in though; one step at a time.

Here's an example showing this working, including rejection of a 
spurious editor backup file in the directory:

$ cat $PGDATA/postgresql.conf | grep ^work_mem
$ tail -n 1 $PGDATA/postgresql.conf
includedir='conf.d'
$ ls $PGDATA/conf.d
00config.conf  00config.conf~
$ cat $PGDATA/conf.d/00config.conf
work_mem=4MB
$ cat $PGDATA/conf.d/00config.conf~
work_mem=2MB
$ psql -c "select name,setting,sourcefile,sourceline from pg_settings 
where name='work_mem'"
    name   | setting |                      
sourcefile                       | sourceline
----------+---------+-------------------------------------------------------+------------
  work_mem | 4096    | 
/home/gsmith/pgwork/data/confdir/conf.d/00config.conf |          1

No docs in here yet.  There's one ugly bit of code here I was hoping 
(but failed) to avoid.  Right now the server doesn't actually save the 
configuration directory anywhere.  Once you leave the initial read in 
SelectConfigFiles, that information is gone, and you only have the 
configfile.  I decided to make that configdir into a global value.  
Seemed easier than trying to pass it around, given how many SIGHUP paths 
could lead to this new code.

I can see some potential confusion here in one case.  Let's say someone 
specifies a full path to their postgresql.conf file.  They might assume 
that the includedir was relative to the directory that file is in.  
Let's say configfile is /etc/sysconfig/pgsql/postgresql.conf ; a user 
might think that "includedir conf.d" from there would reference 
/etc/sysconfig/pgsql/conf.d instead of the $PGDATA/conf.d you actually 
get.  Wavering on how to handle that is one reason I didn't try 
documenting this yet, the decision I made here may not actually be the 
right one.

-- 
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us