[Gluster-devel] autodelete in snapshots

[Rahul Hinduja]

+rajesh

----- Original Message -----
> From: "M S Vishwanath Bhat" <msvbhat at gmail.com>
> To: "Vijay Bellur" <vbellur at redhat.com>
> Cc: "Lalatendu Mohanty" <lmohanty at redhat.com>, "Avra Sengupta" <asengupt at redhat.com>, "Raghavendra Bhat"
> <rabhat at redhat.com>, "Gluster Devel" <gluster-devel at gluster.org>, "Rahul Hinduja" <rhinduja at redhat.com>, "Seema
> Naik" <senaik at redhat.com>
> Sent: Tuesday, June 3, 2014 1:02:08 AM
> Subject: Re: [Gluster-devel] autodelete in snapshots
> 
> On 2 June 2014 20:22, Vijay Bellur <vbellur at redhat.com> wrote:
> 
> > On 04/23/2014 05:50 AM, Vijay Bellur wrote:
> >
> >> On 04/20/2014 11:42 PM, Lalatendu Mohanty wrote:
> >>
> >>> On 04/16/2014 11:39 AM, Avra Sengupta wrote:
> >>>
> >>>> The whole purpose of introducing the soft-limit is, that at any point
> >>>> of time the number of
> >>>> snaps should not exceed the hard limit. If we trigger auto-delete on
> >>>> hitting hard-limit, then
> >>>> the purpose itself is lost, because at that point we would be taking a
> >>>> snap, making the limit
> >>>> hard-limit + 1, and then triggering auto-delete, which violates the
> >>>> sanctity of the hard-limit.
> >>>> Also what happens when we are at hard-limit + 1, and another snap is
> >>>> issued, while auto-delete
> >>>> is yet to process the first delete. At that point we end up at
> >>>> hard-limit + 1. Also what happens
> >>>> if for a particular snap the auto-delete fails.
> >>>>
> >>>> We should see the hard-limit, as something set by the admin keeping in
> >>>> mind the resource consumption
> >>>> and at no-point should we cross this limit, come what may. If we hit
> >>>> this limit, the create command
> >>>> should fail asking the user to delete snaps using the "snapshot
> >>>> delete" command.
> >>>>
> >>>> The two options Raghavendra mentioned are applicable for the
> >>>> soft-limit only, in which cases on
> >>>> hitting the soft-limit
> >>>>
> >>>> 1. Trigger auto-delete
> >>>>
> >>>> or
> >>>>
> >>>> 2. Log a warning-message, for the user saying the number of snaps is
> >>>> exceeding the snap-limit and
> >>>> display the number of available snaps
> >>>>
> >>>> Now which of these should happen also depends on the user, because the
> >>>> auto-delete option
> >>>> is configurable.
> >>>>
> >>>> So if the auto-delete option is set as true, auto-delete should be
> >>>> triggered and the above message
> >>>> should also be logged.
> >>>>
> >>>> But if the option is set as false, only the message should be logged.
> >>>>
> >>>> This is the behaviour as designed. Adding Rahul, and Seema in the
> >>>> mail, to reflect upon the
> >>>> behaviour as well.
> >>>>
> >>>> Regards,
> >>>> Avra
> >>>>
> >>>
> >>> This sounds correct. However we need to make sure that the usage or
> >>> documentation around this should be good enough , so that users
> >>> understand the each of the limits correctly.
> >>>
> >>>
> >> It might be better to avoid the usage of the term "soft-limit".
> >> soft-limit as used in quota and other places generally has an alerting
> >> connotation. Something like "auto-deletion-limit" might be better.
> >>
> >>
> > I still see references to "soft-limit" and auto deletion seems to get
> > triggered upon reaching soft-limit.
> >
> > Why is the ability to auto delete not configurable? It does seem pretty
> > nasty to go about deleting snapshots without obtaining explicit consent
> > from the user.
> >
> 
> I agree with Vijay here. It's not good to delete a snap (even though it is
> oldest) without the explicit consent from user.
> 
> FYI It took me more than 2 weeks to figure out that my snaps were getting
> autodeleted after reaching "soft-limit". For all I know I had not done
> anything and my snap restore were failing.
> 
> I propose to remove the terms "soft" and "hard" limit. I believe there
> should be a limit (just "limit") after which all snapshot creates should
> fail with proper error messages. And there can be a water-mark after which
> user should get warning messages. So below is my proposal.
> 
> *auto-delete + snap-limit:  *If the snap-limit is set to *n*, next snap
> create (n+1th) will succeed *only if* *if auto-delete is set to on/true/1*
> and oldest snap will get deleted automatically. If autodelete is set to
> off/false/0 , (n+1)th snap create will fail with proper error message from
> gluster CLI command.  But again by default autodelete should be off.
> 
> *snap-water-mark*: This should come in picture only if autodelete is turned
> off. It should not have any meaning if auto-delete is turned ON. Basically
> it's usage is to give the user warning that limit almost being reached and
> it is time for admin to decide which snaps should be deleted (or which
> should be kept)
> 
> *my two cents*
> 
> -MS
> 
> 
> >
> > Cheers,
> >
> > Vijay
> >
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>