Thread: freebsd/softupdates for data dir

freebsd/softupdates for data dir

From
Miguel
Date:
Hi, reading the archives i cant find a clear answer about softupdates in
freebsd, is it recommended to enable it for the data directory?

---
miguel

Re: freebsd/softupdates for data dir

From
Mark Kirkwood
Date:
Miguel wrote:
> Hi, reading the archives i cant find a clear answer about softupdates in
> freebsd, is it recommended to enable it for the data directory?
>

There is a pretty good article about softupdates and journelling here:

http://www.usenix.org/publications/library/proceedings/usenix2000/general/full_papers/seltzer/seltzer_html/index.html

and in the freebsd docs here:

http://www.freebsd.org/doc/handbook/configtuning-disk.html

Postgres does not do a lot of file meta-data operations (unless you do a
*lot* of CREATE/DROP INDEX/TABLE/DATABASE), so the performance gains
associated with softupdates will probably be minimal.

I've always left them on, and never had any issues...(even after
unscheduled power loss - which happened here yesterday). As I understand
it, the softupdate code reorders *metadata* operations, and does not
alter data operations - so the effect of fysnc(2) on a preexisting file
is not changed by softupdates being on or off.

Cheers

Mark

Re: freebsd/softupdates for data dir

From
Vivek Khera
Date:
On Apr 3, 2006, at 10:10 PM, Mark Kirkwood wrote:

> I've always left them on, and never had any issues...(even after
> unscheduled power loss - which happened here yesterday). As I
> understand it, the softupdate code reorders *metadata* operations,
> and does not alter data operations - so the effect of fysnc(2) on a
> preexisting file is not changed by softupdates being on or off.

This is also my understanding, and I also leave softupdates on for
the data partition.  Even if it doesn't improve performance, it will
not reduce it, and otherwise does no harm with respect to postgres'
disk usage.


Re: freebsd/softupdates for data dir

From
Jim Nasby
Date:
On Apr 4, 2006, at 10:41 AM, Vivek Khera wrote:
> On Apr 3, 2006, at 10:10 PM, Mark Kirkwood wrote:
>
>> I've always left them on, and never had any issues...(even after
>> unscheduled power loss - which happened here yesterday). As I
>> understand it, the softupdate code reorders *metadata* operations,
>> and does not alter data operations - so the effect of fysnc(2) on
>> a preexisting file is not changed by softupdates being on or off.
>
> This is also my understanding, and I also leave softupdates on for
> the data partition.  Even if it doesn't improve performance, it
> will not reduce it, and otherwise does no harm with respect to
> postgres' disk usage.

More importantly, it allows the system to come up and do fsck in the
background. If you've got a large database that's a pretty big benefit.
--
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461



Re: freebsd/softupdates for data dir

From
Vivek Khera
Date:
On Apr 5, 2006, at 6:07 PM, Jim Nasby wrote:

>
> More importantly, it allows the system to come up and do fsck in
> the background. If you've got a large database that's a pretty big
> benefit.

That's a UFS2 feature, not a soft-updates feature.


Re: freebsd/softupdates for data dir

From
"Jim C. Nasby"
Date:
On Thu, Apr 06, 2006 at 09:45:34AM -0400, Vivek Khera wrote:
>
> On Apr 5, 2006, at 6:07 PM, Jim Nasby wrote:
>
> >
> >More importantly, it allows the system to come up and do fsck in
> >the background. If you've got a large database that's a pretty big
> >benefit.
>
> That's a UFS2 feature, not a soft-updates feature.

It's both. You can't background fsck with softupdates disabled.
--
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461