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Old 02-03-2010, 11:37 AM
Akemi Yagi
 
Default atime, relatime query

On Wed, Feb 3, 2010 at 2:20 AM, Rajagopal Swaminathan
<raju.rajsand@gmail.com> wrote:

> I am aware that mounting filesystems with noatime option greatly
> increases speed.
>
> I have tried to follow discussion on the pros and cons of using noatime.
>
> I have however not been able to mount with the option relatime in centos 5.2.

The relatime option seems to have some issue at this moment:

http://lists.centos.org/pipermail/centos/2009-July/079698.html

The patch was offered by a forum user and it was proposed to be
included in the centosplus kernel. However, that did not work out.
All the details are here:

http://bugs.centos.org/view.php?id=3956

Akemi
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Old 02-03-2010, 11:38 AM
James Hogarth
 
Default atime, relatime query

On 3 February 2010 10:20, Rajagopal Swaminathan <raju.rajsand@gmail.com> wrote:
> Greetings,
>
> I am aware that mounting filesystems with noatime option greatly
> increases speed.
>
> I have tried to follow discussion on the pros and cons of using noatime.
>
> I have however not been able to mount with the option relatime in centos 5.2.
>
> But in a production db server, which is backed up by HP DP, is it
> advisable to mount with noatime?
>
> Anybody care to share their experience on it?
>
> Regards
>
> Rajagopal
> _______________________________________________
> CentOS mailing list
> CentOS@centos.org
> http://lists.centos.org/mailman/listinfo/centos
>

All of my DB systems and more importantly integration and functional
testing systems are noatime and there is a marked difference in
performance - literally cutting testing time by at least half... There
is a lot of disk I/O in that...

RHEL doesn't have a reltime enabled kernel so centos doesn't either by
default. I believe that there is a kernel in plus that is reltime
enabled but due to potentially breaking ABI compatibility with RHEL I
don't make use of it.

James
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Old 02-03-2010, 11:52 AM
Akemi Yagi
 
Default atime, relatime query

On Wed, Feb 3, 2010 at 4:38 AM, James Hogarth <james.hogarth@gmail.com> wrote:

> RHEL doesn't have a reltime enabled kernel so centos doesn't either by
> default. I believe that there is a kernel in plus that is reltime
> enabled but due to potentially breaking ABI compatibility with RHEL I
> don't make use of it.

As you can see in my earlier note (and the referenced bug tracker)
that was posted almost at the same time as yours, when I attempted to
add a relatime patch to the centosplus kernel, it did break the kABI.
Therefore it was not applied (there was a workaround however).

At any rate, the point I wanted to make is that the centosplus kernel
must remain (and has been) kABI-compatible with the distro/RHEL
kernel.

Akemi
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Old 02-03-2010, 12:22 PM
James Hogarth
 
Default atime, relatime query

On 3 February 2010 12:52, Akemi Yagi <amyagi@gmail.com> wrote:
> On Wed, Feb 3, 2010 at 4:38 AM, James Hogarth <james.hogarth@gmail.com> wrote:
>
>> RHEL doesn't have a reltime enabled kernel so centos doesn't either by
>> default. I believe that there is a kernel in plus that is reltime
>> enabled but due to potentially breaking ABI compatibility with RHEL I
>> don't make use of it.
>
> As you can see in my earlier note (and the referenced bug tracker)
> that was posted almost at the same time as yours, when I attempted to
> add a relatime patch to the centosplus kernel, it did break the kABI.
> Therefore it was not applied (there was a workaround however).
>
> At any rate, the point I wanted to make is that the centosplus kernel
> must remain (and has been) kABI-compatible with the distro/RHEL
> kernel.
>
> Akemi
> _______________________________________________
> CentOS mailing list
> CentOS@centos.org
> http://lists.centos.org/mailman/listinfo/centos
>

Ah thanks Akemi - I thought the plus repository existed as something
that might break ABI compatibility - I'm pleasantly surprised to find
I'm wrong if not the case

And I saw your post just after I made mine (I must have been typing
the same time as you) and you definitely covered the material better.

James
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Old 02-03-2010, 07:45 PM
"nate"
 
Default atime, relatime query

Rajagopal Swaminathan wrote:

> But in a production db server, which is backed up by HP DP, is it
> advisable to mount with noatime?

noatime typically helps when dealing with lots of files, most DB servers
have a small number of files that are large in size, so noatime is
likely not to provide any noticeable improvement I think.

nate


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Old 02-03-2010, 08:09 PM
Les Mikesell
 
Default atime, relatime query

On 2/3/2010 2:45 PM, nate wrote:
> Rajagopal Swaminathan wrote:
>
>> But in a production db server, which is backed up by HP DP, is it
>> advisable to mount with noatime?
>
> noatime typically helps when dealing with lots of files, most DB servers
> have a small number of files that are large in size, so noatime is
> likely not to provide any noticeable improvement I think.

On the other hand you are unlikely to miss it on most filesystems,
especially any that you back up with a file-oriented mechanism like tar
or rsync. The only time it matters is for rare apps like a mail client
that might try to notify you when your mailbox has been written more
recently than the last read.

--
Les Mikesell
lesmikesell@gmail.com


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Old 02-03-2010, 08:15 PM
Rob Kampen
 
Default atime, relatime query

nate wrote:

Rajagopal Swaminathan wrote:



But in a production db server, which is backed up by HP DP, is it
advisable to mount with noatime?



noatime typically helps when dealing with lots of files, most DB servers
have a small number of files that are large in size, so noatime is
likely not to provide any noticeable improvement I think.

nate

I do not agree - every read of the db will update the filesystem with
noatime missing, thus specifying noatime does give performance
improvements - the size of the files does not matter as much - rather
the number of reads vs writes.

just my $0.02 worth


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Old 02-03-2010, 09:33 PM
"nate"
 
Default atime, relatime query

Rob Kampen wrote:

> I do not agree - every read of the db will update the filesystem with
> noatime missing, thus specifying noatime does give performance
> improvements - the size of the files does not matter as much - rather
> the number of reads vs writes.

Interesting, didn't think about that aspect, I dug around and at least
for MySQL and Postgresql noatime doesn't appear to provide any
noticeable benefit(it may be a measurable one in some cases)

http://www.mysqlperformanceblog.com/2007/11/01/innodb-performance-optimization-basics/

http://www.ffnn.nl/pages/articles/linux/server-wide-performance-benchmarking.php

If your doing a ton of reads and only have a few files, it's likely
there isn't going to be many atime updates as the file is kept open
for an extended period of time(e.g. scanning a table with 100k rows).

For DB performance there's a lot more useful areas to spend time
tuning. As DBAs often say you can get 10% more performance tuning
the OS and getting better hardware, and you can get 1000% better
performance by tuning the queries and data structures, or something
like that


nate


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Old 02-04-2010, 07:37 AM
Rajagopal Swaminathan
 
Default atime, relatime query

Greetings,

On Thu, Feb 4, 2010 at 4:03 AM, nate <centos@linuxpowered.net> wrote:
> Rob Kampen wrote:
>
> For DB performance there's a lot more useful areas to spend time
> tuning. As DBAs often say you can get 10% more performance tuning
> the OS and getting better hardware, and you can get 1000% better
> performance by tuning the queries and data structures, or something
> like that

Thanks Akemi, James, Nate, Les and Rob for the replies and lively discussion.

For time being till I am convinced that HP DataProtect does not need
atime, I will have to leave them on.

Of course, I have noatime for non-critical systems as my usual practice.

Regards,

Rajagopal
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