Are we sure that performance concerns aren't manifested in 'real' environments? 
I think we should make some more effort to validate that assumption.

I agree with all the points below, but the worst part of the logging is the 
readability. Right now the log is fine for developers and support but  from a 
user's point of view we may as well write it out in hex - it's very hard to 
decipher and makes self support for users very difficult.

We should default to INFO mode which should be understandable, and switching to 
debug should be simple and ideally possible from ovirt-engine.

Saggi Mizrahi <> wrote:

of course you are right and just having everything log in debug is less then 
We do only save 100 logs back so this will not fill up a decently sized hard 

The performance implication though existing don't really pop up in normal use.

It's true we usually don't need logs that far back but as I said it's really 
not an issue.
Even when you try and run a 1000 VMs you will not be blocked on logging trying 
to get written to disk I can assure you of that.

There are a lot of things we can do to improve the size footprint and 
readability of our logs.
The move to XZ instead of GZ was a simple way to save on space and there are 
plans on using an even more compressed representation for old logs.
We are also working on tools to help manage the log files.

You are correct though that setting the logging level back or changing the 
amount of logs kept shouldn't be such a bothersome process and you should open 
a bug on that for VDSM and it will be fixed.

----- Original Message -----
> From: "Peter Portante" <>
> To: "Saggi Mizrahi" <>
> Cc:
> Sent: Thursday, April 5, 2012 3:57:08 PM
> Subject: Re: [vdsm] /etc/rc.c/init.d/vdsmd set filters for libvirt at DEBUG 
> level
> Hi Saggi,
> ----- Original Message -----
> > From: "Saggi Mizrahi" <>
> > To: "Peter Portante" <>
> > Cc:
> > Sent: Thursday, April 5, 2012 3:02:23 PM
> > Subject: Re: [vdsm] /etc/rc.c/init.d/vdsmd set filters for libvirt
> > at DEBUG level
> > 
> > It's required for support purposes. When something goes wrong we
> > collect all the logs from the hosts, this way we can figure out
> > whats wrong without requiring someone to reproduce the problem with
> > the logging turned on.
> > 
> > We are working on making the logs easier to filter when inspecting
> > them.
> > But the general idea is, if the information is in when can easily
> > get
> > it out, but doing it the other way around is impossible.
> While one can understand the pain of debugging complex systems,
> respectfully, this approach seems more problematic than helpful.
> First, it was filling up the system disk. In 10 minutes there were
> four compressed log files for libvirt alone, not to mention the
> vdsmd.log files. Talking with the rest of the performance team, we
> always turn all this off so that we don't loose our systems while
> testing.
> Additionally to get the logging to stop, one has to modify the vdsmd
> start up script to get libvirt to stop logging so much. Each time a
> modification was made to libvirt's configuration file to make it
> stop, libvirt kept up all its debug logging. All the documentation
> on the libvirt web page tells one what to do to affect its behavior,
> but in the presence of vdsm that is not the case. Somehow, that
> seems like a problem to have one subsystem completely override
> another with leaving any indication that it is doing so.
> Second, it is expensive to have such overhead. Compressing and
> maintaining arbitrary sized log files of text takes processing time
> away from the VMs. It was amazing to see how often xz would run on a
> box, not knowing it was related to maintaining these log files.
> There must be a better way than collecting all the data we could
> possibly need ahead of time just in case a problem comes up.
> Have you considered asserting the expected state of the system before
> embarking on changing that state?
> > In a nutshell order to filter out debug messages grep -v is you
> > friend.
> grep -v is not useful when your system disk fills up. :)
> And Why wouldn't an attacker use that fact in some sort of denial of
> service?  And if the counter is to configure the log files so that
> they are processed more often and kept to a small number, then as
> the amount of data grows (like when multiple VMs are created) the
> original problem will get lost as it is truncated.
> So if we already a finite data set of sorts, why not drop using log
> files in favor of using a dedicated ring buffer that stores
> ultra-compressed binary data (enough to track the problem) with a
> tool that can format that ring buffer into useable output.
> When we were writing the thread library for Tru64 Unix and OpenVMS,
> such ring buffers were invaluable to help find complicated timing
> problems across multiple processors.
> Respectfully,
> -peter
> Ps - Blessed Passover to you!
> > 
> > ----- Original Message -----
> > > From: "Peter Portante" <>
> > > To:
> > > Sent: Thursday, April 5, 2012 10:51:15 AM
> > > Subject: [vdsm] /etc/rc.c/init.d/vdsmd set filters for libvirt at
> > > DEBUG level
> > > 
> > > Hello Folks,
> > > 
> > > I built vdsm from git and installed it on my system, and found
> > > that
> > > vdsm's init scripts are setting libvirt's logging levels to
> > > debug.
> > > 
> > > I was quite puzzled for a time trying to modify libvirt's config
> > > file
> > > to reduce the logging levels to warning, as it seemed that the
> > > vdsm
> > > install had placed proper settings in the libvirt config file
> > > itself.
> > > 
> > > Is there some history behind this log filter setting in the init
> > > scripts of vdsm that I should know about? Is the debug logging
> > > level
> > > of libvirt required for the correct operation of vdsm?
> > > 
> > > Thanks,
> > > 
> > > -peter
> > > _______________________________________________
> > > vdsm-devel mailing list
> > >
> > >
> > > 
> > 
vdsm-devel mailing list
vdsm-devel mailing list

Reply via email to