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From Xikui Wang <xik...@uci.edu>
Subject Re: MultiTransactionJobletEventListenerFactory
Date Fri, 17 Nov 2017 05:46:45 GMT
Yes. That deadlock could happen. Currently, we have one-to-one mappings for
the jobs and transactions, except for the feeds.

@Abdullah, after some digging into the code, I think probably we can use a
single transaction id for the job which feeds multiple datasets? See if I
can convince you. :)

The reason we have multiple transaction ids in feeds is that we compile
each connection job separately and combine them into a single feed job. A
new transaction id is created and assigned to each connection job, thus for
the combined job, we have to handle the different transactions as they
are embedded in the connection job specifications. But, what if we create a
single transaction id for the combined job? That transaction id will be
embedded into each connection so they can write logs freely, but the
transaction will be started and committed only once as there is only one
feed job. In this way, we won't need multiTransactionJobletEventListener
and the transaction id can be removed from the job specification easily as
well (for Steven's change).

Best,
Xikui


On Thu, Nov 16, 2017 at 4:26 PM, Mike Carey <dtabass@gmail.com> wrote:

> I worry about deadlocks.  The waits for graph may not understand that
> making t1 wait will also make t2 wait since they may share a thread -
> right?  Or do we have jobs and transactions separately represented there
> now?
>
> On Nov 16, 2017 3:10 PM, "abdullah alamoudi" <bamousaa@gmail.com> wrote:
>
> > We are using multiple transactions in a single job in case of feed and I
> > think that this is the correct way.
> > Having a single job for a feed that feeds into multiple datasets is a
> good
> > thing since job resources/feed resources are consolidated.
> >
> > Here are some points:
> > - We can't use the same transaction id to feed multiple datasets. The
> only
> > other option is to have multiple jobs each feeding a different dataset.
> > - Having multiple jobs (in addition to the extra resources used, memory
> > and CPU) would then forces us to either read data from external sources
> > multiple times, parse records multiple times, etc
> >   or having to have a synchronization between the different jobs and the
> > feed source within asterixdb. IMO, this is far more complicated than
> having
> > multiple transactions within a single job and the cost far outweigh the
> > benefits.
> >
> > P.S,
> > We are also using this for bucket connections in Couchbase Analytics.
> >
> > > On Nov 16, 2017, at 2:57 PM, Till Westmann <tillw@apache.org> wrote:
> > >
> > > If there are a number of issue with supporting multiple transaction ids
> > > and no clear benefits/use-cases, I’d vote for simplification :)
> > > Also, code that’s not being used has a tendency to "rot" and so I think
> > > that it’s usefulness might be limited by the time we’d find a use for
> > > this functionality.
> > >
> > > My 2c,
> > > Till
> > >
> > > On 16 Nov 2017, at 13:57, Xikui Wang wrote:
> > >
> > >> I'm separating the connections into different jobs in some of my
> > >> experiments... but that was intended to be used for the experimental
> > >> settings (i.e., not for master now)...
> > >>
> > >> I think the interesting question here is whether we want to allow one
> > >> Hyracks job to carry multiple transactions. I personally think that
> > should
> > >> be allowed as the transaction and job are two separate concepts, but I
> > >> couldn't find such use cases other than the feeds. Does anyone have a
> > good
> > >> example on this?
> > >>
> > >> Another question is, if we do allow multiple transactions in a single
> > >> Hyracks job, how do we enable commit runtime to obtain the correct TXN
> > id
> > >> without having that embedded as part of the job specification.
> > >>
> > >> Best,
> > >> Xikui
> > >>
> > >> On Thu, Nov 16, 2017 at 1:01 PM, abdullah alamoudi <
> bamousaa@gmail.com>
> > >> wrote:
> > >>
> > >>> I am curious as to how feed will work without this?
> > >>>
> > >>> ~Abdullah.
> > >>>> On Nov 16, 2017, at 12:43 PM, Steven Jacobs <sjaco002@ucr.edu>
> wrote:
> > >>>>
> > >>>> Hi all,
> > >>>> We currently have MultiTransactionJobletEventListenerFactory, which
> > >>> allows
> > >>>> for one Hyracks job to run multiple Asterix transactions together.
> > >>>>
> > >>>> This class is only used by feeds, and feeds are in process of
> > changing to
> > >>>> no longer need this feature. As part of the work in pre-deploying
> job
> > >>>> specifications to be used by multiple hyracks jobs, I've been
> working
> > on
> > >>>> removing the transaction id from the job specifications, as we
use a
> > new
> > >>>> transaction for each invocation of a deployed job.
> > >>>>
> > >>>> There is currently no clear way to remove the transaction id from
> the
> > job
> > >>>> spec and keep the option for MultiTransactionJobletEventLis
> > tenerFactory.
> > >>>>
> > >>>> The question for the group is, do we see a need to maintain this
> class
> > >>> that
> > >>>> will no longer be used by any current code? Or, an other words,
is
> > there
> > >>> a
> > >>>> strong possibility that in the future we will want multiple
> > transactions
> > >>> to
> > >>>> share a single Hyracks job, meaning that it is worth figuring out
> how
> > to
> > >>>> maintain this class?
> > >>>>
> > >>>> Steven
> > >>>
> > >>>
> >
> >
>

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