databases and xen?

databases and xen?

[Nicholas Lee]

I'm wondering how stable/realiable Xen 2.0 is for running databases in a
guest domain with filesystems mounted via LVM.

I noted the benchmarks used postgres, but I'm wondering about real world
use.

Thanks.
Nicholas 


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databases and xen?

[Nicholas Lee]

I'm wondering how stable/realiable Xen 2.0 is for running databases in a guest domain with filesystems mounted via LVM.


Nicholas



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Re: databases and xen?

[Wim Coekaerts]

testign it has already been fine. I ran 4 databases each in one domain
(oracle10g) and it s been amazingly stable. I have not however done
performance testing. soon...

On Mon, Jan 17, 2005 at 10:55:28PM +1300, Nicholas Lee wrote:
> I'm wondering how stable/realiable Xen 2.0 is for running databases in a 
> guest domain with filesystems mounted via LVM.
> 
> 
> Nicholas
> 
> 
> 
> -------------------------------------------------------
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> _______________________________________________
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Re: databases and xen?

[Rik van Riel]

On Mon, 17 Jan 2005, Wim Coekaerts wrote:

> testign it has already been fine. I ran 4 databases each in one domain
> (oracle10g) and it s been amazingly stable. I have not however done
> performance testing. soon...

How does O_DIRECT IO to xen block devices work ?

Does it make it to disk atomically, or does that still
need some patches ?

-- 
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it." - Brian W. Kernighan


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Re: databases and xen?

[Ian Pratt]

> On Mon, 17 Jan 2005, Wim Coekaerts wrote:
> 
> > testign it has already been fine. I ran 4 databases each in one domain
> > (oracle10g) and it s been amazingly stable. I have not however done
> > performance testing. soon...
> 
> How does O_DIRECT IO to xen block devices work ?

I'm not entirely sure quite what O_DIRECT is defined to do. It
probably bypasses the guest's buffer cache OK, and gets turned
into IO's in domain 0 without passing through the buffer cache
(unless you're using a loop file or suchlike).

I believe IOs wont be acknowledged to the guest until they've
been completed in dom0. However, they can be reordered. We
probably need to add in a re-order barrier operation on the VBD
device channel protocol in order to guarantee ordering where it
matters (this would be marginally more efficient than
holding back following requests in the guest).


Ian


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Re: databases and xen?

[Matt Ayres]

On Tue, 2005-01-18 at 20:45 +0000, Ian Pratt wrote:
> > On Mon, 17 Jan 2005, Wim Coekaerts wrote:
> > 
> > > testign it has already been fine. I ran 4 databases each in one domain
> > > (oracle10g) and it s been amazingly stable. I have not however done
> > > performance testing. soon...
> > 
> > How does O_DIRECT IO to xen block devices work ?
> 
> I'm not entirely sure quite what O_DIRECT is defined to do. It
> probably bypasses the guest's buffer cache OK, and gets turned
> into IO's in domain 0 without passing through the buffer cache
> (unless you're using a loop file or suchlike).
> 
> I believe IOs wont be acknowledged to the guest until they've
> been completed in dom0. However, they can be reordered. We
> probably need to add in a re-order barrier operation on the VBD
> device channel protocol in order to guarantee ordering where it
> matters (this would be marginally more efficient than
> holding back following requests in the guest).
> 

To avoid the buffercache problems of loopback images in dom0 you can
have dom0 open the loop files with O_DIRECT.  This should help
performance when using loop files as it eliminates the double buffering.

> 
> Ian
> 
> 
> -------------------------------------------------------
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> _______________________________________________
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> https://lists.sourceforge.net/lists/listinfo/xen-devel
-- 



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Re: databases and xen?

[Moshe Bar]

I have run Mysql and Oracle 9i without any problems on 2.0.0 and 2.0.1 
, but I didn't have LVM (don't think that would create problems)

Moshe


On Jan 17, 2005, at 11:55 AM, Nicholas Lee wrote:

> I'm wondering how stable/realiable Xen 2.0 is for running databases in 
> a guest domain with filesystems mounted via LVM.
>
>
> Nicholas
>
>
>
> -------------------------------------------------------
> The SF.Net email is sponsored by: Beat the post-holiday blues
> Get a FREE limited edition SourceForge.net t-shirt from ThinkGeek.
> It's fun and FREE -- well, almost....http://www.thinkgeek.com/sfshirt
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/xen-devel
>



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Re: databases and xen?

[Nicholas Lee]

On Tue, Jan 18, 2005 at 04:02:01AM +0200, Moshe Bar wrote:
> I have run Mysql and Oracle 9i without any problems on 2.0.0 and 2.0.1 
> , but I didn't have LVM (don't think that would create problems)

I would have thought that using loopback/file or NFS VBD would have
caused performance issue and lost of database guarantees.

Or does a fsync on a File VBD get pushed though to the host (dom0)?

Nicholas


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Re: databases and xen?

[Kip Macy]

On Tue, 18 Jan 2005, Nicholas Lee wrote:

> On Tue, Jan 18, 2005 at 04:02:01AM +0200, Moshe Bar wrote:
> > I have run Mysql and Oracle 9i without any problems on 2.0.0 and 2.0.1
> > , but I didn't have LVM (don't think that would create problems)
>
> I would have thought that using loopback/file or NFS VBD would have
> caused performance issue and lost of database guarantees.

It definitely causes performance degradation, but that is certainly not
the only way to set a domain up, merely the cheapest. The I/O syncer is
all going to be managed from DOM0, so if the guest crashes
transactional integrity is maintained. If the HW crashes you have the
same issues as with ext2. If you want integrity guarantees and high
performance you'll likely want a fibre channel device exported to the
guest.


> Or does a fsync on a File VBD get pushed though to the host (dom0)?
There is no fsync on a block device. An I/O should only be acknowledged
when the device commits it. Nonetheless, on Linux I would wager that it
stays in the buffer cache until the syncer gets around to flushing it.



				-Kip



>
> Nicholas
>
>
> -------------------------------------------------------
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>


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Re: databases and xen?

[Fajar A. Nugraha]

Nicholas Lee wrote:

> I'm wondering how stable/realiable Xen 2.0 is for running databases in 
> a guest domain with filesystems mounted via LVM.

In my experience, it's very reliable for normal usage.
I run apache + php + rrdttol + mysql on Xen running on gnbd-imported devices
(I was interested in the live migrate feature). It was great for normal 
usage.

The live migrate was rather buggy though. Occasionally (not often) I found
domains can't be accessed at all after migrated. This was with Xen 2.0.
I haven't tested 2.0.3 much.

IMHO LVM-based storage should be better (in performance) than gnbd.

Regards,

Fajar


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