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

[Raghavendra Gowdappa]

----- 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

> 
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