Re: [Gluster-devel] Question about random and rr scheduler

[Craig Tierney]

Amar S. Tumballi wrote:
> On Mon, Mar 3, 2008 at 4:27 PM, Craig Tierney <address@hidden>
> wrote:
>
> > I setting up Gluster (1.3.7) with two servers.  I first
> > tried configuring the clients as round-robin (rr). When I try and write
> > to the filesystem for the first time, all of the files go
> > to the first brick.  Subsequent writes will alternate between
> > the two bricks.  When I try random, the first file is always
> > created on the first brick.  Subsequent writes always go to
> > the first brick (never the second).
>
> As the name suggests 'random' scheduler just calls random() and it just does
> % with the number of clients. Hence, not much control over it by user side
> right now.

> > What I want is round-robin, or a working random.  However,
> > for round-robin to work for me, I need the chosen server to
> > be random, not always the first one.
> >
> > In the long-term, it wouldn't really matter because everything
> > would average out.  However, I am creating filesystems that
> > will be temporary, so I need the right behavior in the short term.
> >
> > Should random do what I need?  Should I look in the code
> > and see how to get the Round-Robin schedule to start with
> > a random index?
>
> Just initialize index variable in rr scheduler to start with a random
> number. should not be much of a work..


I modified the rr scheduler to use a random index at initialization.
I like the behavior much better.


--- glusterfs-1.3.7/scheduler/rr/src/rr.c       2007-10-05 05:57:12.000000000 
+0000
+++ ../glusterfs-1.3.7/scheduler/rr/src/rr.c    2008-03-04 14:53:10.191215255 
+0000
@@ -49,7 +49,10 @@
     trav_xl = trav_xl->next;
   }
   rr_buf->child_count = index;
-  rr_buf->sched_index = 0;
+
+  srandom(time(NULL)); /* Initialize the seed */
+  rr_buf->sched_index = random()%index; /* Randomize the initial index */
+
   rr_buf->array = calloc (index + 1, sizeof (struct rr_sched_struct));
   trav_xl = xl->children;
   index = 0;

Craig
--
Craig Tierney (address@hidden)