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From Alexey Goncharuk <alexey.goncha...@gmail.com>
Subject Re: Getting rid of NONE cache rebalance mode
Date Tue, 28 Jul 2020 15:19:40 GMT
Ivan,

Sorry for a delay in reply. Yes, I was thinking about the same use-case,
and in this particular case an unexpected load on a 3rd-party database
manifests itself. I am not sure how expiration relates to the partition
ownership - once a partition moves to a renting state, all entries are
eagerly cleaned from the memory, so there is no need for expiration.

Can you elaborate on your idea how rebalancing relates to expiration?

вт, 21 июл. 2020 г. в 15:59, Ivan Pavlukhin <vololo100@gmail.com>:

> Alexey,
>
> Thank you for explanation. I feel that I miss a couple bits to
> understand the picture fully. I am thinking about a case which I tend
> to call a Memcached use-case. There is a cache over underlying storage
> with read-through and expiration and without any rebalancing at all.
> When new nodes enter they take ownership for some partitions from
> already running nodes and serve client requests. Entries for not
> owning anymore partitions expire according to configuration.
>
> Actually, I have an idea. My guess is that "rebalancing" is a smarter
> and better approach than waiting for expiration. Am I right?
>
> 2020-07-21 15:31 GMT+03:00, Alexey Goncharuk <alexey.goncharuk@gmail.com>:
> > Ivan,
> >
> > In my understanding this mode does not work at all even in the presence
> of
> > ForceKeysRequest which is now supposed to fetch values from peers in case
> > of a miss. In this mode we 1) move partitions to OWNING state
> > unconditionally, and 2) choose an arbitrary OWNING node for force keys
> > request. Therefore, after a user started two additional nodes in a
> cluster,
> > the request may be mapped to a node which does not hold any data. We will
> > do a read-through in this case, but it will result in significant load
> > increase on a third-party storage right after a node started, which means
> > that adding a node will increase, not decrease, the load on the database
> > being cached.
> > All these issues go away when (A)SYNC mode is used.
> >
> > Val,
> > The idea makes sense to me - a user can use rebalance future to wait for
> > rebalance to finish. This will simplify the configuration even further.
> >
> > пн, 20 июл. 2020 г. в 21:27, Valentin Kulichenko <
> > valentin.kulichenko@gmail.com>:
> >
> >> +1 for deprecating/removing NONE mode.
> >>
> >> Alexey, what do you think about the SYNC mode? In my experience, it does
> >> not add much value as well. I would go as far as removing the
> >> rebalancingMode parameter altogether (probably in 3.0).
> >>
> >> -Val
> >>
> >> On Mon, Jul 20, 2020 at 11:09 AM Ivan Pavlukhin <vololo100@gmail.com>
> >> wrote:
> >>
> >> > Alexey, Igniters,
> >> >
> >> > Could you please outline motivation answering following questions?
> >> > 1. Does this mode generally work correctly today?
> >> > 2. Can this mode be useful at all?
> >> >
> >> > I can imagine that it might be useful in a transparent caching use
> >> > case (if I did not misunderstand).
> >> >
> >> > 2020-07-20 20:39 GMT+03:00, Pavel Tupitsyn <ptupitsyn@apache.org>:
> >> > > +1
> >> > >
> >> > > More evidence:
> >> > >
> >> >
> >>
> https://stackoverflow.com/questions/62902640/apache-ignite-cacherebalancemode-is-not-respected-by-nodes
> >> > >
> >> > > On Mon, Jul 20, 2020 at 8:26 PM Alexey Goncharuk
> >> > > <alexey.goncharuk@gmail.com>
> >> > > wrote:
> >> > >
> >> > >> Igniters,
> >> > >>
> >> > >> I would like to run the idea of deprecating and probably ignoring
> >> > >> the
> >> > >> NONE
> >> > >> rebalance mode by the community. It's in the removal list for
> Ignite
> >> 3.0
> >> > >> [1], but it looks like it still confuses and creates issues for
> >> > >> users
> >> > >> [2].
> >> > >>
> >> > >> What about deprecating it in one of the next releases and even
> >> ignoring
> >> > >> this constant in further releases, interpreting it as ASYNC, before
> >> > >> Ignite
> >> > >> 3.0? I find it hard to believe that any Ignite user actually has
> >> > >> RebalanceMode.NONE set in their configuration due to its absolutely
> >> > >> unpredictable behavior.
> >> > >>
> >> > >> Thanks for your thoughts,
> >> > >> --AG
> >> > >>
> >> > >> [1]
> >> > >>
> >> > >>
> >> >
> >>
> https://cwiki.apache.org/confluence/display/IGNITE/Apache+Ignite+3.0+Wishlist
> >> > >> [2]
> >> > >>
> >> > >>
> >> >
> >>
> http://apache-ignite-developers.2346864.n4.nabble.com/About-Rebalance-Mode-SYNC-amp-NONE-td47279.html
> >> > >>
> >> > >
> >> >
> >> >
> >> > --
> >> >
> >> > Best regards,
> >> > Ivan Pavlukhin
> >> >
> >>
> >
>
>
> --
>
> Best regards,
> Ivan Pavlukhin
>

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