[Gluster-devel] [Gluster-users] [DHT] The myth of two hops for linkto file resolution

Raghavendra Gowdappa rgowdapp at redhat.com
Fri May 5 05:02:53 UTC 2017

----- Original Message -----
> From: "Pranith Kumar Karampuri" <pkarampu at redhat.com>
> To: "Raghavendra Gowdappa" <rgowdapp at redhat.com>
> Cc: "Gluster Devel" <gluster-devel at gluster.org>, "gluster-users" <gluster-users at gluster.org>
> Sent: Thursday, May 4, 2017 4:03:18 PM
> Subject: Re: [Gluster-users] [DHT] The myth of two hops for linkto file resolution
> On Sun, Apr 30, 2017 at 9:33 AM, Raghavendra Gowdappa <rgowdapp at redhat.com>
> wrote:
> > All,
> >
> > Its a common perception that the resolution of a file having linkto file
> > on the hashed-subvol requires two hops:
> >
> > 1. client to hashed-subvol.
> > 2. client to the subvol where file actually resides.
> >
> > While it is true that a fresh lookup behaves this way, the other fact that
> > get's ignored is that fresh lookups on files are almost always prevented by
> > readdirplus. Since readdirplus picks the dentry from the subvolume where
> > actual file (data-file) resides, the two hop cost is most likely never
> > witnessed by the application.
> >
> > A word of caution is that I've not done any testing to prove this
> > observation :).
> >
> May be you should do it and send an update. That way we can use the
> knowledge to do something.

I understand the importance of performance numbers. But, I am tied up with other things :). We can measure them when we really need this information. If you (or anyone else) have anything lined up which needs this data, please let me know and I can devote sometime to provide it. Till then, Other things take high priority.


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