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Accumulo, mail # dev - Tserver zookeeper locks


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Re: Tserver zookeeper locks
John Vines 2013-06-22, 03:32
Nope, that is sufficient. That solves that mystery.

Thanks Keith.
On Fri, Jun 21, 2013 at 6:53 PM, Keith Turner <[EMAIL PROTECTED]> wrote:

> John,
>
> I think this code is just to avoid race conditions between the master and
> tserver.
>
> The tserver will create a node X and then create an ephemeral node Y under
> X.   Y is the lock.   So the code helps avoid the following situation.
>
>  * tserver creates X
>  * master sees X has no children/locks and deletes X
>  * tserver tries to create Y as a child of X and fails because X does not
> exist
>
> It seems like above situation may have caused some sort of problem, but I
> can not remember.  So I think the delayed delete may have been added to
> avoid a problem.  I can try to dig up tickets if you need more info.
>
> Keith
>
> On Fri, Jun 21, 2013 at 6:13 PM, John Vines <[EMAIL PROTECTED]> wrote:
>
> > Eric probably knows the answer to this, but if anyone else can chime in
> it
> > would be great.
> >
> >
> > LiveTServerSet is what is used to maintain the set of all functional
> > tservers the master is aware of. Part of the logic for it is when it
> finds
> > that a znode for a tserver (tserver lock) goes missing, it will mark is
> as
> > lockless as well as reporting it as doomed to the master. The latter
> action
> > has the master try to phase it out of everything, etc.
> >
> > The lockless part of it though seems a little foreign, but it may be
> > because my branch has changed substantially around ZooCache. It appears
> to
> > wait 10 minutes and if it is still lockless it will delete the lock
> > explicitly. But isn't the lock already gone? Or is the lock znode empty
> vs.
> > nonexistant?
> >
>