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

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/
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