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From Sergey Shelukhin <ser...@hortonworks.com>
Subject Re: assignment - is master beeing a watchdog useful?
Date Thu, 06 Dec 2012 18:18:19 GMT
I may be missing some past context here, but why not make it so that the
assignment zookeeper node is ephemeral, so it dies with the server?
Then it will be possible to notice there's no more assignment without the
separate watcher.

I have conflicting opinions about the current safeguard; on one hand, I've
seen at least one bug (HBASE-6060) that was fixed (on 0.96 but explicitly
not in 0.94) that resulted in region never being assigned (until the 30min
watcher kicked in, that is).
On the other hand, making catch-alls for code bugs in this manner seems
like a bad practice.
Maybe we can remove it when we have "bulletproof" unit(!) tests for AM that
take into account various scenarios.

On Thu, Dec 6, 2012 at 9:26 AM, Jimmy Xiang <jxiang@cloudera.com> wrote:

> Currently, rs doesn't watch the znode.  RS cancels ongoing open after
> master tells it so.
>
> Jimmy
>
> On Wed, Dec 5, 2012 at 7:53 PM, Stack <stack@duboce.net> wrote:
> > On Wed, Dec 5, 2012 at 6:57 PM, Jimmy Xiang <jxiang@cloudera.com> wrote:
> >
> >> If this region server happens to be hot, it may take a while to open
> >> it.  If we don't time it out, the server may be even hotter.  If the
> >> region server could not open it here, other region servers may not be
> >> able to open it either.
> >>
> >
> >
> > I suppose the master can still 'timeout' the open if the RS is watching
> the
> > znode for the region it is trying to open.  The RS will notice that
> master
> > has assumed control in a callback and can then cancel any ongoing open.
> >
> > St.Ack
>

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