[Engine-devel] alias in disk instead of name

Charlie medievalist at gmail.com
Tue Oct 23 18:41:15 UTC 2012 

Very good points, Simon.  I do usually think in terms of large data
centers, but certainly not on the scale of cloud service providers!
Not yet, anyway.

It wouldn't be hard to restructure the algorithm as lockless, but if
you're really anticipating a scenario where hundreds of thousands of
users are all going to try to simultaneously create the same name,
there's (at least theoretically) a nasty edge case where one user
loops on name prompts until he goes nuts and throws the computer out
the window.

--Chaarlie

On Tue, Oct 23, 2012 at 2:07 PM, Simon Grinberg <simon at redhat.com> wrote:
>
>
> ----- Original Message -----
>> From: "Charlie" <medievalist at gmail.com>
>> To: "Simon Grinberg" <simon at redhat.com>
>> Cc: "engine-devel" <engine-devel at ovirt.org>
>> Sent: Tuesday, October 23, 2012 7:53:10 PM
>> Subject: Re: [Engine-devel] alias in disk instead of name
>>
>> Why not something like this?
>>
>> (pseudocode, using dot for string concatenation):
>>
>> $name_prefix = "vmdrive"
>> $name = get_last_used($name_prefix)
>> $already_in_use = $TRUE
>>
>> while $already_in_use {
>>      prompt "Name of thing? [$name] ", $name
>>      if name_used($name) {
>>          while name_used($name) {
>>             increment_number($name)
>>          }
>>      } else {
>>          $already_in_use = FALSE
>>      }
>> }
>>
>> do_whatever_you_do_with($name)
>>
>> store_last_used($name)
>>
>> end
>>
>>
>> The increment_number() routine checks to see if the last character is
>> numeric, and if it is, increments the leftmost contiguous numeric
>> portion of the string.  Otherwise it appends the number zero.
>>
>> This does not allow everyone to get any name they want, but you can't
>> ever satisfy that demand.  It supplies reasonable defaults very
>> quickly and it allows people who want really descriptive names to try
>> as many as they like.
>>
>> The code's built the funny way it is so that you can corrupt the db
>> that holds the last_used numbers or interrupt the process halfway
>> through and it still works, only slower, and it should tend to fix
>> its
>> own db on the fly when possible.
>>
>> There's no provision for simultaneous creation, but that wouldn't be
>> horribly hard to add, just put a lock on the resource holding
>> last_used numbers.
>>
>> You'd want to reimplement in the most efficient and readable way for
>> your programming language of choice.
>>
>> Did that make any sense?  I did it off the top of my head, so it
>> could
>> be terribly lame when I look at it tomorrow ;).
>
> Please don't look at it as pure programming item, nor as a single user in a small data center - in this respect you are right.
> Let's got to a huge organization or to the cloud.
>
> In multi tenant environment this lock means that every time a user tries to change a disk name - all the others are stack
> Don't forget we are discussing thousands of VMs - I'll hate to have this kind of lock just to allow for unique disk names. This is one of the reasons you use UUID to really identify the object in the DB, since it's suppose to guarantee uniqueness without the need to lock everything.
>
> And again - please look at this as an end user, why do I care that other users had decided they are going to use the same name as me? This is my human readable name and I want to choose what ever I like without considering other users. What is this self service portal worth if I can't name my VMs and Disks as I'd like to, oblivious to others?
>
> At the end of day, you want oVirt to be useful and scalable - and not just code wise correct.
>
>
>>
>> --Charlie
>>
>> On Tue, Oct 23, 2012 at 1:10 PM, Simon Grinberg <simon at redhat.com>
>> wrote:
>> >
>> >
>> > ----- Original Message -----
>> >> From: "Charlie" <medievalist at gmail.com>
>> >> To: "Simon Grinberg" <simon at redhat.com>
>> >> Cc: "engine-devel" <engine-devel at ovirt.org>
>> >> Sent: Tuesday, October 23, 2012 6:51:35 PM
>> >> Subject: Re: [Engine-devel] alias in disk instead of name
>> >>
>> >> OK, only because you asked...
>> >>
>> >> Provide default unique names, so that users can just press enter
>> >> if
>> >> names don't matter to them.  That way you obviate the entire
>> >> argument;
>> >> people who need special naming can have it, and everybody else has
>> >> a
>> >> single extra keypress or mouseclick at naming time, and searching
>> >> works well enough.
>> >>
>> >> You can name the first one vmdrive0 and increment the numeric part
>> >> each time a new drive is created.  Iterating until an unused name
>> >> is
>> >> found isn't so computationally expensive that anyone should weep,
>> >> especially if you store the last used number and do an
>> >> incrementing
>> >> sanity check against it at naming time.
>> >
>> > Let's say the above solved all conflicts when coming to create a
>> > new disk, it does seems so.
>> >
>> > Let's say that import/export if names conflict can be solved in a
>> > reasonable way - for example forcing (somehow and without
>> > bothering the user too much) a rename of the disk (How would you
>> > know if the conflicting name id auto-generated so can be replaced
>> > or user provided?, you'll have to resort to
>> > non-that-human-look-alike-name)
>> >
>> > How does it solve the multi-tenancy use case?
>> > I'm tenant A, setting up a quorum disk for my two VMs - so I call
>> > this disk simply quorum.
>> > Now comes tenant B, he is also setting up a quorum disk, so he
>> > tries to call his disk quorum
>> >
>> > But no,
>> > He'll get a popup that this name is already taken - bad luck buddy.
>> > Now he needs to guess the next available name? Would you build in
>> > algorithm to suggest alternatives?
>> > Why should tenant B care in the first place that tenant A also
>> > wanted to call his disk 'quorum'?
>> >
>> > Same with the VM name - but that is given for now, though I hope to
>> > convince it should change in the future.
>> >
>> > What I'm trying to say here - infrastructure is for the admin - so
>> > you can force uniqueness
>> > Resources like, disks and Virtual Machine belong to the end user
>> > thus you should let them determine their own names without being
>> > restricted by users of the system.
>> >
>> >
>> >
>> >>
>> >> People expect names to have significance, and we like it when they
>> >> have both unique and non-unique parts.  It's part of our human
>> >> heritage.  Maybe whales and dolphins don't care.
>> >
>> >
>> >
>> >>
>> >> --Charlie
>> >>
>> >> On Tue, Oct 23, 2012 at 4:36 AM, Simon Grinberg <simon at redhat.com>
>> >> wrote:
>> >> >
>> >> > We need more thoughts here from others, there are two different
>> >> > approaches on the table and more opinions are welcomed.
>> >> > If there are API consumers on this list then your view is more
>> >> > then
>> >> > welcomed.
>> >> >
>> >> > Thanks,
>> >> > Simon.
>> >> >
>> >> > ----- Original Message -----
>> >> >> From: "Simon Grinberg" <simon at redhat.com>
>> >> >> To: "Michael Pasternak" <mpastern at redhat.com>
>> >> >> Cc: "engine-devel" <engine-devel at ovirt.org>
>> >> >> Sent: Monday, October 22, 2012 10:50:02 AM
>> >> >> Subject: Re: [Engine-devel] alias in disk instead of name
>> >> >>
>> >> >>
>> >> >>
>> >> >> ----- Original Message -----
>> >> >> > From: "Michael Pasternak" <mpastern at redhat.com>
>> >> >> > To: "Simon Grinberg" <simon at redhat.com>
>> >> >> > Cc: "engine-devel" <engine-devel at ovirt.org>
>> >> >> > Sent: Monday, October 22, 2012 8:58:25 AM
>> >> >> > Subject: Re: [Engine-devel] alias in disk instead of name
>> >> >> >
>> >> >> > On 10/21/2012 06:13 PM, Simon Grinberg wrote:
>> >> >> > >
>> >> >> > >
>> >> >> > > ----- Original Message -----
>> >> >> > >> From: "Michael Pasternak" <mpastern at redhat.com>
>> >> >> > >> To: "Simon Grinberg" <simon at redhat.com>
>> >> >> > >> Cc: "engine-devel" <engine-devel at ovirt.org>
>> >> >> > >> Sent: Sunday, October 21, 2012 4:56:33 PM
>> >> >> > >> Subject: Re: [Engine-devel] alias in disk instead of name
>> >> >> > >>
>> >> >> > >> On 10/21/2012 04:15 PM, Simon Grinberg wrote:
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>> ----- Original Message -----
>> >> >> > >>>> From: "Michael Pasternak" <mpastern at redhat.com>
>> >> >> > >>>> To: "Simon Grinberg" <simon at redhat.com>
>> >> >> > >>>> Cc: "engine-devel" <engine-devel at ovirt.org>
>> >> >> > >>>> Sent: Sunday, October 21, 2012 3:48:46 PM
>> >> >> > >>>> Subject: Re: [Engine-devel] alias in disk instead of
>> >> >> > >>>> name
>> >> >> > >>>>
>> >> >> > >>>> On 10/21/2012 03:36 PM, Simon Grinberg wrote:
>> >> >> > >>>>>
>> >> >> > >>>>> ----- Original Message -----
>> >> >> > >>>>>>> From: "Michael Pasternak" <mpastern at redhat.com>
>> >> >> > >>>>>>> To: "engine-devel" <engine-devel at ovirt.org>
>> >> >> > >>>>>>> Sent: Sunday, October 21, 2012 12:26:46 PM
>> >> >> > >>>>>>> Subject: [Engine-devel] alias in disk instead of name
>> >> >> > >>>>>>>
>> >> >> > >>>>>>>
>> >> >> > >>>>>>> The problem we caused by using alias in disk instead
>> >> >> > >>>>>>> of
>> >> >> > >>>>>>> name
>> >> >> > >>>>>>> is
>> >> >> > >>>>>>> break
>> >> >> > >>>>>>> of search-by-name paradigm
>> >> >> > >>>>>>> in engine.search dialect, not sure why we do not want
>> >> >> > >>>>>>> forcing
>> >> >> > >>>>>>> disk
>> >> >> > >>>>>>> name to be unique [1],
>> >> >> > >>>>>>> but lack of "name" in disk search is does not look
>> >> >> > >>>>>>> good
>> >> >> > >>>>>>> in
>> >> >> > >>>>>>> my
>> >> >> > >>>>>>> view.
>> >> >> > >>>>>>>
>> >> >> > >>>>>>> thoughts?
>> >> >> > >>>>>>>
>> >> >> > >>>>>>> [1] can be easily achieved via appropriate
>> >> >> > >>>>>>> can-do-action
>> >> >> > >>>>>>> verification.
>> >> >> > >>>>> Names by definition are not unique IDs,
>> >> >> > >>>>
>> >> >> > >>>> they do, otherwise /search wasn't effective, remember
>> >> >> > >>>> users
>> >> >> > >>>> not
>> >> >> > >>>> exposed to entity id, all entities fetched by-name, so
>> >> >> > >>>> names
>> >> >> > >>>> has
>> >> >> > >>>> to
>> >> >> > >>>> be unique.
>> >> >> > >>>
>> >> >> > >>> Yap that is what we do with many entities, and it causes
>> >> >> > >>> problems.
>> >> >> > >>> But with disks it is multiplied
>> >> >> > >>>
>> >> >> > >>>>
>> >> >> > >>>>> thus it should not be enforced.
>> >> >> > >>>>> What would be the auto naming conversion to ensure
>> >> >> > >>>>> uniqueness
>> >> >> > >>>>> with
>> >> >> > >>>>> plain text?
>> >> >> > >>>>
>> >> >> > >>>> not sure i follow, i'll assume you refer here to empty
>> >> >> > >>>> name, -
>> >> >> > >>>> you
>> >> >> > >>>> cannot have an
>> >> >> > >>>> entity with no name.
>> >> >> > >>>
>> >> >> > >>> Well you create a new disk - do we want to enforce the
>> >> >> > >>> user
>> >> >> > >>> to
>> >> >> > >>> provide a unique disk name/alias for every disk he
>> >> >> > >>> creates?
>> >> >> > >>> This will drive the user crazy. This is important even
>> >> >> > >>> for
>> >> >> > >>> user
>> >> >> > >>> only for floating/shared disks. For any other disks user
>> >> >> > >>> does
>> >> >> > >>> not
>> >> >> > >>> care if it's disk1, hd1, whatever. For these kind of
>> >> >> > >>> disk,
>> >> >> > >>> it's
>> >> >> > >>> just a VM disk and the user does not care if in all VMs
>> >> >> > >>> this
>> >> >> > >>> is
>> >> >> > >>> called disk 1 - so why bother him?
>> >> >> > >>
>> >> >> > >> from the same reason we have unique
>> >> >> > >> clusters/datacenters/networks/templates/etc...
>> >> >> > >
>> >> >> > > Networks, DataCenter, Clusters, templates - are in order of
>> >> >> > > magnitude less then the number of disks.
>> >> >> > > And you name once and use many.
>> >> >> > >
>> >> >> > > As for VMs - well it's may take that we should not force
>> >> >> > > uniqueness
>> >> >> > > either ( you can warn though )
>> >> >> >
>> >> >> > you cannot have two vms with same name in same domain ...
>> >> >>
>> >> >> I didn't say that in a domain you are allowed to have two
>> >> >> guests
>> >> >> with
>> >> >> the same hostname, I've said engine should allow for having
>> >> >> duplicate VM names.
>> >> >> You are assuming that the VM name is identical to the guest
>> >> >> host
>> >> >> name.
>> >> >>
>> >> >> For many this is the case, for other it's just an alias/name
>> >> >> given
>> >> >> in
>> >> >> oVirt.
>> >> >> Actually for the cloud, this is mostly going to be the case and
>> >> >> worse, you are blocking different tenants from having the same
>> >> >> VM
>> >> >> name just because you are assuming that VM name = guest
>> >> >> hostname.
>> >> >>
>> >> >> >
>> >> >> > >
>> >> >> > > For disks, well number is >= VMs to >>>= VMs
>> >> >> > > Name by definition is mostly interesting in many cases only
>> >> >> > > within
>> >> >> > > the VM, and we don't even have a way to correlate disk
>> >> >> > > alias
>> >> >> > > to
>> >> >> > > the internal name in the VM. In many cases as said before,
>> >> >> > > a
>> >> >> > > user
>> >> >> > > won't care about the name/alias if it is always attached to
>> >> >> > > the
>> >> >> > > same VM. A user will rather look the VM and then list it's
>> >> >> > > disk.
>> >> >> > > So actually I'll be better off with vm1.disk1 vm2.disk2
>> >> >> > > then
>> >> >> > > unique name per disk (PS AFAIK) this should be the default
>> >> >> > > suggested name by the UI, but then changing the VM name
>> >> >> > > will
>> >> >> > > break
>> >> >> > > this (yes, I know it's not possible ATM, but many people I
>> >> >> > > know
>> >> >> > > requested for that).
>> >> >> > >
>> >> >> > > So I as user will prefer that all the disks that created
>> >> >> > > from
>> >> >> > > a
>> >> >> > > template will have the same name as the original template,
>> >> >> > > and
>> >> >> > > then to be able to search by (vm=name, disk=name) thus I
>> >> >> > > can
>> >> >> > > access easily the same disk for the VMs.
>> >> >> > >
>> >> >> > > On the other hand for others, as you've mentioned
>> >> >> > > (especially
>> >> >> > > for
>> >> >> > > floating and shared disk) the name/alias may be of
>> >> >> > > importance,
>> >> >> > > uniqueness may be very important.
>> >> >> >
>> >> >> > any disk can become shared.
>> >> >>
>> >> >> Then when you make it shared then bother to give it a
>> >> >> meaningful
>> >> >> alias
>> >> >>
>> >> >> >
>> >> >> > >
>> >> >> > > All that I'm saying that we can't force it's not that
>> >> >> > > uniqueness
>> >> >> > > in
>> >> >> > > never desired.
>> >> >> >
>> >> >> > simon, you missing the point, i was talking about /search,
>> >> >> > search is available only at /api/disks (i.e shared disks,
>> >> >> > vm/template.disks is
>> >> >> > irrelevant to this discussion)
>> >> >>
>> >> >> Nope I do not, but I think that our perspectives differ.
>> >> >> You are looking at it as strictly design issue. You have a
>> >> >> collection
>> >> >> of entities and you want a human readable search, thus you are
>> >> >> trying to force (rightfully) from your point of view a unique
>> >> >> alias/name for those.
>> >> >>
>> >> >> I taking the end user perspective, and user experience
>> >> >> 1. Majority of the disks have no meaning outside of a VM scope.
>> >> >> 2. There are fractions of the disks that are usually shared
>> >> >> (this
>> >> >> is
>> >> >> the nature of shared disks)
>> >> >> 3. There are fractions of floating, most of the floating will
>> >> >> be a
>> >> >> transient state, while you are moving disks around.
>> >> >>
>> >> >> What I'm trying to say that forcing a user to provide a unique
>> >> >> name
>> >> >> per disk is a huge bother.
>> >> >> And again in the multi tenancy case, you can't enforce a unique
>> >> >> alias
>> >> >> in the system.
>> >> >>
>> >> >> What will you say to the user in the error message?
>> >> >> Sorry you can't use this alias since another user that is
>> >> >> sharing
>> >> >> the
>> >> >> system with you already provided that name? And yes we know you
>> >> >> can't see that other disk, and it you don't care about the
>> >> >> other
>> >> >> user, but still you can't use your alias since this is how our
>> >> >> platform designed.
>> >> >>
>> >> >> The meaning is that you must allow a for a more sophisticated
>> >> >> search.
>> >> >> Yes even in the context of the disks tab. Disks are not really
>> >> >> stand
>> >> >> alone entities, and if we keep to strict conventions like - in
>> >> >> any
>> >> >> collection an entity name must be unique, then you are making
>> >> >> the
>> >> >> system hardly usable for many users.
>> >> >>
>> >> >> So a search in disks should include other 'properties' (and yes
>> >> >> I
>> >> >> know those are not disk properties, but this is how a user will
>> >> >> look
>> >> >> at it) like owner,quota,vm,storage domain, etc.
>> >> >>
>> >> >> To some up - what should be unique are UUIDs of an entities,
>> >> >> and
>> >> >> infrastructure entities names (within the same scope) - all the
>> >> >> rest
>> >> >> must not.
>> >> >>
>> >> >>
>> >> >> >
>> >> >> > >
>> >> >> > >>
>> >> >> > >>>
>> >> >> > >>>>
>> >> >> > >>>>> Would you change these on import/export?
>> >> >> > >>>>
>> >> >> > >>>> would you mind elaborating on this?
>> >> >> > >>>
>> >> >> > >>> Yes,
>> >> >> > >>>
>> >> >> > >>> You are already facing a problem when importing VMs that
>> >> >> > >>> already
>> >> >> > >>> have the same name, now you increasing the problem for
>> >> >> > >>> disks
>> >> >> > >>> that
>> >> >> > >>> have the same alias. for same name we force clone if you
>> >> >> > >>> want
>> >> >> > >>> to
>> >> >> > >>> import. Why for clone just because of a disk alias (this
>> >> >> > >>> implies
>> >> >> > >>> collapse snapshots ATM) or even bother the user with
>> >> >> > >>> renaming
>> >> >> > >>> disks that he does not care about the name so he just
>> >> >> > >>> gave
>> >> >> > >>> disk
>> >> >> > >>> 1,
>> >> >> > >>> 2, 3 and so on?
>> >> >> > >>
>> >> >> > >> i see your point, but then we leave no option for the user
>> >> >> > >> to
>> >> >> > >> locate
>> >> >> > >> the disk,
>> >> >> > >> simply because he doesn't have unique identifier,
>> >> >> > >>
>> >> >> > >> just imagine user A creating disk and calling it X,
>> >> >> > >> then user B creating disk and calling it X, they on
>> >> >> > >> different
>> >> >> > >> domains etc., and now both want to use disk X,
>> >> >> > >>
>> >> >> > >> how they can figure out which one to pick?, by SD, by
>> >> >> > >> size?
>> >> >> > >> agree
>> >> >> > >> this is doesn't look well..., even more than that -
>> >> >> > >> someone
>> >> >> > >> may
>> >> >> > >> call
>> >> >> > >> this "bad design"...
>> >> >> > >
>> >> >> > > This is why the search should accept more then the name.
>> >> >> > > Example (vm=name, disk=name/alias)
>> >> >> > > Example (dc=name, disk=name/alias)
>> >> >> > > Example (sd=name, disk=name/alias)
>> >> >> >
>> >> >> > it's not about accepting both name/alias, it's about missing
>> >> >> > ability
>> >> >> > to identify your resource in collection.
>> >> >> >
>> >> >> > > For floating/shared on the same SD/DC/VM I would suggest a
>> >> >> > > warning
>> >> >> > > if there is a duplicate in the system - not enforcement.
>> >> >> >
>> >> >> > ok, lets assume we WARN user that his disk's name is not
>> >> >> > unique,
>> >> >> > how
>> >> >> > user will pick the unique name?
>> >> >> > implementing own code checking if new name (he wants to use)
>> >> >> > is
>> >> >> > unique or not?
>> >> >> >
>> >> >> > - this is business logic, not user's prerogative.
>> >> >> >
>> >> >> > > There is a difference between best practice and being
>> >> >> > > enforcing
>> >> >> > > up
>> >> >> > > to the level that it annoys some of the users.
>> >> >> >
>> >> >> > simon, when you register to email, you have to try N times
>> >> >> > till
>> >> >> > you
>> >> >> > find unique username,
>> >> >> > is it convenient? absolutely NO, is it annoying? YES, but you
>> >> >> > forced
>> >> >> > doing that so
>> >> >> > system will be able to identify you,
>> >> >> >
>> >> >> > it's no different in any way, good software protects
>> >> >> > user/itself
>> >> >> > even
>> >> >> > in cost of convenience,
>> >> >> >
>> >> >> > bottom line
>> >> >> > ===========
>> >> >> >
>> >> >> > - i think as long as disk not shared/floating it can have any
>> >> >> > name
>> >> >> > - in a minute disk designation changed to shared, name
>> >> >> > uniqueness
>> >> >> > should be forced (by the engine)
>> >> >> > - when importing vm with shared disks, name uniqueness should
>> >> >> > be
>> >> >> > forced
>> >> >> > - when creating vm from template with shared disk, name
>> >> >> > uniqueness
>> >> >> > should be forced
>> >> >> > - alias should be changed back to name (in sake of
>> >> >> > consistency)
>> >> >> > - /api/disks collection should support searching disks by
>> >> >> > name
>> >> >> > (in
>> >> >> > sake of consistency)
>> >> >> >
>> >> >> >
>> >> >> > thoughts?
>> >> >>
>> >> >> Please look at the previous comment, that just can't work in
>> >> >> the
>> >> >> multi-tenancy case.
>> >> >> Name should not be unique, the warning is for the admin only,
>> >> >> from
>> >> >> the user portal a warning should be issues only if the user
>> >> >> provides
>> >> >> same name twice.
>> >> >>
>> >> >>
>> >> >> >
>> >> >> > >
>> >> >> > >>
>> >> >> > >>
>> >> >> > >> --
>> >> >> > >>
>> >> >> > >> Michael Pasternak
>> >> >> > >> RedHat, ENG-Virtualization R&D
>> >> >> > >> _______________________________________________
>> >> >> > >> Engine-devel mailing list
>> >> >> > >> Engine-devel at ovirt.org
>> >> >> > >> http://lists.ovirt.org/mailman/listinfo/engine-devel
>> >> >> > >>
>> >> >> >
>> >> >> >
>> >> >> > --
>> >> >> >
>> >> >> > Michael Pasternak
>> >> >> > RedHat, ENG-Virtualization R&D
>> >> >> > _______________________________________________
>> >> >> > Engine-devel mailing list
>> >> >> > Engine-devel at ovirt.org
>> >> >> > http://lists.ovirt.org/mailman/listinfo/engine-devel
>> >> >> >
>> >> >>
>> >> > _______________________________________________
>> >> > Engine-devel mailing list
>> >> > Engine-devel at ovirt.org
>> >> > http://lists.ovirt.org/mailman/listinfo/engine-devel
>> >>
>>

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