[Engine-devel] Guid & NGuid

[Alon Bar-Lev]

----- Original Message -----
> From: "Michael Kublin" <mkublin at redhat.com>
> To: engine-devel at ovirt.org
> Sent: Monday, February 4, 2013 2:15:40 PM
> Subject: Re: [Engine-devel] Guid & NGuid
> 
> 
> 
> ----- Original Message -----
> > From: "Mike Kolesnik" <mkolesni at redhat.com>
> > To: "Michael Kublin" <mkublin at redhat.com>
> > Cc: engine-devel at ovirt.org
> > Sent: Monday, February 4, 2013 11:48:45 AM
> > Subject: Re: [Engine-devel] Guid & NGuid
> > 
> > ----- Original Message -----
> > > 
> > > 
> > > ----- Original Message -----
> > > > From: "Laszlo Hornyak" <lhornyak at redhat.com>
> > > > To: "Michael Kublin" <mkublin at redhat.com>
> > > > Cc: engine-devel at ovirt.org
> > > > Sent: Monday, February 4, 2013 9:56:28 AM
> > > > Subject: Re: [Engine-devel] Guid & NGuid
> > > > 
> > > > 
> > > > 
> > > > ----- Original Message -----
> > > > > From: "Michael Kublin" <mkublin at redhat.com>
> > > > > To: engine-devel at ovirt.org
> > > > > Sent: Monday, February 4, 2013 8:47:29 AM
> > > > > Subject: Re: [Engine-devel] Guid & NGuid
> > > > > 
> > > > > 
> > > > > 
> > > > > ----- Original Message -----
> > > > > > From: "Roy Golan" <rgolan at redhat.com>
> > > > > > To: engine-devel at ovirt.org
> > > > > > Sent: Monday, February 4, 2013 9:18:21 AM
> > > > > > Subject: Re: [Engine-devel] Guid & NGuid
> > > > > > 
> > > > > > On 02/03/2013 03:19 PM, Alon Bar-Lev wrote:
> > > > > > >
> > > > > > > ----- Original Message -----
> > > > > > >> From: "Omer Frenkel" <ofrenkel at redhat.com>
> > > > > > >> To: "Michael Kublin" <mkublin at redhat.com>
> > > > > > >> Cc: "engine-devel" <engine-devel at ovirt.org>
> > > > > > >> Sent: Sunday, February 3, 2013 3:12:19 PM
> > > > > > >> Subject: Re: [Engine-devel] Guid & NGuid
> > > > > > >>
> > > > > > >>
> > > > > > >>
> > > > > > >> ----- Original Message -----
> > > > > > >>> From: "Michael Kublin" <mkublin at redhat.com>
> > > > > > >>> To: "engine-devel" <engine-devel at ovirt.org>
> > > > > > >>> Sent: Sunday, February 3, 2013 3:10:14 PM
> > > > > > >>> Subject: [Engine-devel] Guid & NGuid
> > > > > > >>>
> > > > > > >>> Hi,
> > > > > > >>>
> > > > > > >>> In ovirt-engine code we have Guid and NGuid objects.
> > > > > > >>> Guid is extends NGuid and also NGuid class has method
> > > > > > >>> getValue()
> > > > > > >>> which should return Guid.
> > > > > > >>> As for me these two classes are look like the same and
> > > > > > >>> I
> > > > > > >>> don't
> > > > > > >>> see
> > > > > > >>> to
> > > > > > >>> much differences between them.
> > > > > > >>> My proposal is to remove NGuid and move it
> > > > > > >>> functionality
> > > > > > >>> to
> > > > > > >>> Guid
> > > > > > >>> (Because of Guid is much more common)
> > > > > > >>>
> > > > > > >> i agree, but we need to take another step forward and
> > > > > > >> allow
> > > > > > >> Guid
> > > > > > >> to
> > > > > > >> be null (as it should)
> > > > > > >> and not assume its EMPTY or have a value (i'm pretty
> > > > > > >> sure
> > > > > > >> we
> > > > > > >> have
> > > > > > >> this assumption in many places)
> > > > > > > Hi,
> > > > > > >
> > > > > > > And for the new people out here... why not kill both and
> > > > > > > use
> > > > > > > plain
> > > > > > > standard java UUID[1]?
> > > > > > +1 for using java.util.UUID
> > > > > > 
> > > > > > NGuid functionality that should be extracted during the
> > > > > > refactor
> > > > > > is
> > > > > > -
> > > > > > 1. refactor DB and Java so empty or null return values are
> > > > > > null
> > > > > > and
> > > > > > not
> > > > > > EMPTY_GUID
> > > > > > 2. the special constructor of NGuid for UUID return by
> > > > > > Microsoft
> > > > > > AD
> > > > > > should be extracted to a factory/utility
> > > > > > > I think we should kill compat, I don't see any value in
> > > > > > > fixing
> > > > > > > anything about it while leaving it intact.
> > > > > > >
> > > > > > > Regards,
> > > > > > > Alon Bar-Lev.
> > > > > > >
> > > > > > > [1]
> > > > > > > http://docs.oracle.com/javase/6/docs/api/java/util/UUID.html
> > > > > Actually there is exists one reason not to use directly UUID
> > > > > at
> > > > > server side.
> > > > > The main operations on Guid today it is to convert object to
> > > > > Guid
> > > > > or
> > > > > Guid to string.
> > > > > Guid it is immutable object, number of Guids is limited and
> > > > > almost
> > > > > never changed,
> > > > > These sound like classical case for object that can be
> > > > > cached.
> > > > > Benefit - reduced number of string manipulations, reduced
> > > > > number
> > > > > of
> > > > > created instances, less work
> > > > > for garbage collection
> > > > 
> > > > UUID has the same properties, it is immutable. So you could do
> > > > the
> > > > same with UUID, but I am not sure you could effectively cache
> > > > these
> > > > objects and prove that you are saving either CPU, heap, or GC
> > > > time.
> > > These is a very common pattern:
> > > 1) implementation of valueOf() for most classes like Integer,
> > > Double,
> > > etc... has some kind of cache.
> > > 2) JVM has cache for strings that can be used and that cache can
> > > be
> > > tweaked by some JVM opts.
> > > 3) Most of our operations is perform query on DB, send request to
> > > host or parse response from host and Guid
> > >    is very common object that is immutable.
> > > I am agree that these will not solve all our performance problems
> > > but
> > > can provide some benefit, especially when it is very easy
> > > to implement.
> > 
> > We could still achieve that using a UUIDCreator class and call it
> > instead of Guid.fromString("")..
> > 
> > Whether this is cached or not is another question which can be
> > solved
> > later and checked to see if the cache improves performance or not.
> These is already implementation, if it will be Guid.fromString("") or
> UUIDCreator.
> The issue is if we want to use cache, it should be implemented
> together
> with deleting/replacing of Guid/NGuid , because of it much more
> easilly

I think the value of using standard java classes is higher than the tuning of the engine at this regard. Dropping the compat thing is important activity.

After doing this conversion, use profiler to determine where major bottle necks are and fix these, I am not sure the above optimization will be first in list. If we invest resources in optimization better to invest in these that we suffer most.

Regards,
Alon