[Engine-devel] Guid & NGuid

[Michael Kublin]

----- 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.