[sheepdog] [Sheepdog] [PATCH 4/4] [PATCH 04/10] sheep: update node information and epoch from

[Yibin Shen]

On Tue, May 15, 2012 at 3:35 PM, Christoph Hellwig <hch at infradead.org> wrote:
> On Tue, May 15, 2012 at 10:53:55AM +0800, Liu Yuan wrote:
>> We actually met this the same problem running zookeeper, when we tried
>> to remove register/un-register group_fd to help main thread get more
>> responsive. The main thread is very unwieldy for now and become a major
>> bottleneck for massive nodes cluster. Our effort is trying to get it
>> slimmer.
>
> I defintively like the register/un-register group_fd removal idea, it
> helps moving work off the main thread, and simplifies the code.
>
> I'd actually like to take some of the concepts there even further,
> e.g. the patch already updates most of the cluster state in join
> synchronously, and the rest of it are the vdi_inuse update and lots
> of tiny synchronous code pathes.  Why not do all of __sd_join_done
> synchronously from sd_join_handler except for the vdi_inuse update,
> and then make sure all code looking at vdi_inuse is executed in its
> own work queue, both for updates and reads from it, which should
> help lifting the VDI operations out of the main thread, even if the
> VDI workqueue remains single threaded by itself.
>
> Pretty similarly the only thing executed in the event queue for
> leaves is check_majority, and I wonder if we can get away with
> executing that after all the cluster state updates currently in
> __sd_leave_done, which except for recovery could then be called
> directly from sd_leave_handler, avoiding the event queue issues.

Agreed,

and in current check_majority code,
there are lots of redundant connection to each node, it's not a good idea.
why not leave the heath check logic with membership management module
(eg. zookeeper/accord/corosync)


/*
 * Check whether the majority of Sheepdog nodes are still alive or not
 */
static int check_majority(struct sd_node *nodes, int nr_nodes)
{
        int nr_majority, nr_reachable = 0, fd, i;
        char name[INET6_ADDRSTRLEN];

        nr_majority = nr_nodes / 2 + 1;

        /* we need at least 3 nodes to handle network partition
         * failure */
        if (nr_nodes < 3)
                return 1;

        for (i = 0; i < nr_nodes; i++) {
                addr_to_str(name, sizeof(name), nodes[i].addr, 0);
                fd = connect_to(name, nodes[i].port);
                if (fd < 0)
                        continue;

                close(fd);
                nr_reachable++;
                if (nr_reachable >= nr_majority) {
                        dprintf("the majority of nodes are alive\n");
                        return 1;
                }
        }
        dprintf("%d, %d, %d\n", nr_nodes, nr_majority, nr_reachable);
        eprintf("the majority of nodes are not alive\n");
        return 0;
}

>
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