[Gluster-devel] About spread count, lookup and layout

[Tahereh Fattahi]

Thanks a lot
I read in document that when we want to create a file, first we should be
sure that this file does not exist in the directory. So first look at the
hashed subvolume and if it does not exist then broad cast this lookup to
other subvolume (when lookup optimize is off) to ensure that this file was
not created before.
I had thought that lookup everywhere is for searching file not for layout.
I want to reduce the lookup for file (not layout) when lookup optimize is
off and compare it when lookup optimize is on. (of course lookup optimize
on is better , I want do this)

On Sun, Apr 30, 2017 at 8:12 AM, Raghavendra Gowdappa <rgowdapp at redhat.com>
wrote:

>
>
> ----- Original Message -----
> > From: "Tahereh Fattahi" <t28.fattahi at gmail.com>
> > To: "Gluster Devel" <gluster-devel at gluster.org>
> > Sent: Sunday, April 30, 2017 8:03:15 AM
> > Subject: [Gluster-devel] About spread count, lookup and layout
> >
> > Hi
> > I have some question about spread count:
> >
> > 1. When I set spread count less than subvolume count, I see the hash is
> > assigned to one directory layout for some subvolumes are zero (that is
> ok) ,
> > but I expect these subvolumes should not bee looked up in case
> > lookup_everywhere for creating a file. Unfortunately I see these lookups
> in
> > server profile.
> > Am I correct?
>
> Yes. lookup-everywhere is a fall back mechanism for the scenarios where
> layout can't be trusted (like in the window b/w fix layout after add/remove
> brick etc and healing of the immediate children of directory as per the new
> layout). Since layout itself can't be trusted, it doesn't matter whether it
> has zero ranges or not. A better way of solving this problem (than
> identifying 0 ranges etc) is lookup-optimize, which identifies scenarios
> (predominantly add/remove brick) and decides whether to use
> lookup-everywhere before saying that a file/directory is not present.
>
> > is there any way for this case to reduce the amount of lookups that is
> send
> > to the servers? (lookup optimize is off and I want this)
>
> Is there any reason why you want lookup-optimize to be off?
>
> >
> > 2. I see the option for changing the spread count and fixing the layout
> in
> > dht xlaor (dht_setxattr), but when I tried to set this attribute and
> change
> > the layout I dont see any change!! while there is no error and crash (I
> call
> > setfattr in client side because I dont see dht xlator in server graph)
>
> Probably there might be bugs in that codepath. Can you please file a bug?
>
> regards,
> Raghavendra
>
> >
> > _______________________________________________
> > Gluster-devel mailing list
> > Gluster-devel at gluster.org
> > http://lists.gluster.org/mailman/listinfo/gluster-devel
>
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