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From Pramod Immaneni <pra...@datatorrent.com>
Subject Re: APEXCORE-619 Recovery windowId in future during application relaunch.
Date Wed, 01 Mar 2017 21:41:21 GMT
Do we need to save committedWindowId? Can't it be computed from existing
checkpoints by walking through the DAG. We probably do this anyway and I
suspect there is a minor bug somewhere in there. If an operator is
stateless you could assume checkpoint as long max for sake of computation
and compute the committed window to be the lowest common checkpoint. If
they are all stateless and you end up with long max you can start with
window id that reflects the current timestamp.

Thanks

On Wed, Mar 1, 2017 at 1:09 PM, Amol Kekre <amol@datatorrent.com> wrote:

> CommitWindowId could be computed from the existing checkpoints. That
> solution still needs purge to be done after commitWindowId is confirmed to
> be saved in Stram state. Without ths the commitWindowId computed from the
> checkpoints may have some checkpoints missing.
>
> Thks
> Amol
>
>
>
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> On Wed, Mar 1, 2017 at 12:36 PM, Pramod Immaneni <pramod@datatorrent.com>
> wrote:
>
> > Can't the commitedWindowId be calculated by looking at the physical plan
> > and the existing checkpoints?
> >
> > On Wed, Mar 1, 2017 at 5:34 AM, Tushar Gosavi <tushar@apache.org> wrote:
> >
> > > Help Needed for APEXCORE-619
> > >
> > > Issue : When application is relaunched after long time with stateless
> > > opeartors at the end of the DAG, the stateless operators starts with a
> > very
> > > high windowId. In this case the stateless operator ignors all the data
> > > received till upstream operator catches up with it. This breaks the
> > > *at-least-once* gaurantee while relaunch of the opeartor or when master
> > is
> > > killed and application is restarted.
> > >
> > > Solutions:
> > > - Fix windowId for stateless leaf operators from upstream opeartor. But
> > it
> > > has some issues when we have a join with two upstrams operators at
> > > different windowId. If we set the windowID to min(upstream windowId),
> > then
> > > we need to again recalulate the new recovery window ids for upstream
> > paths
> > > from this operators.
> > >
> > > - Other solution is to create a empty file in checkpoint directory for
> > > stateless operators. This will help us to identify the checkpoints of
> > > stateless operators during relaunch instead of computing from latest
> > > timestamp.
> > >
> > > - Bring the entire DAG to committedWindowId. This could be achived
> using
> > > writing committedWindowId in a journal. we need to make sure that we
> are
> > > not puring the checkpointed state until the committedWundowId is saved
> in
> > > journal.
> > >
> > > Let me know your thoughs on this and preferred solution.
> > >
> > > Regards,
> > > -Tushar.
> > >
> >
>

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