Re: Proposed doc-patch: Identifying the Current WAL file

[Jeff Frost <jeff(at)frostconsultingllc(dot)com>]

On Sat, 15 Apr 2006, Tom Lane wrote:

> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > Also, what happens if the log switch happens, and some data change is
> > written to the new WAL file in the first second, but nothing happens to
> > the database after that for a minute?  Your test would still show the
> > old log file.
>
> You seem to be assuming that ls will sort on the basis of the truncated
> mtime that it displays, which is not the actual behavior of ls AFAIK.

I believe you're correct, at least with the ls I have here on my linux system. 
I created two files quickly with touch.  Here is the stat output:

  File: `AA'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 802h/2050d      Inode: 2736263     Links: 1
Access: (0644/-rw-r--r--)  Uid: (   26/postgres)   Gid: (   26/postgres)
Access: 2006-04-15 11:02:46.000000000 -0700
Modify: 2006-04-15 11:02:46.000000000 -0700
Change: 2006-04-15 11:02:46.000000000 -0700
  File: `AB'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 802h/2050d      Inode: 2736264     Links: 1
Access: (0644/-rw-r--r--)  Uid: (   26/postgres)   Gid: (   26/postgres)
Access: 2006-04-15 11:02:48.000000000 -0700
Modify: 2006-04-15 11:02:48.000000000 -0700
Change: 2006-04-15 11:02:48.000000000 -0700

ls -t | head -1
AB

So it looks like the original was correct all along, but with Tom's regex it's 
much cleaner.  Too bad grep's regex engine doesn't support {24}.

I'll change all my scripts to use the following:

ls -t /pg_xlog/ | grep '^[0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F][0-9A-F]$' | head -1

Thanks Tom!

 -- 
Jeff Frost, Owner 	<jeff(at)frostconsultingllc(dot)com>
Frost Consulting, LLC 	http://www.frostconsultingllc.com/
Phone: 650-780-7908	FAX: 650-649-1954