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From Valentin Kulichenko <valentin.kuliche...@gmail.com>
Subject Re: Deprecating LOCAL cache
Date Fri, 27 Jul 2018 17:58:43 GMT
Guys,

Use cases for local caches are rare, but they definitely exist. I don't
think it's a very good idea to deprecate this functionality at this point.

At the same point, it's obviously not the most critical part of the
product, so maintaining the whole separate implementation for it is
probably an overkill. We had exact same story with replicated caches btw -
they were implemented separately which caused maintainability issues, and
we ended up removing this separate implementation. If we have the same
situation here, let's use the same solution.

-Val

On Fri, Jul 27, 2018 at 3:05 AM Dmitry Pavlov <dpavlov.spb@gmail.com> wrote:

> Hi Dmitriy,
>
> I would like to stress this: I'm not saying local cache it useless. I'm
> supposing it is not used widely. I want to figure out if I'm mistaking.
>
> All folks involved into user list says it is not used, so why not to
> deprecate? If we make a mistake, somebody will come to user list and say,
> 'Hey, why did you deprecate this, it is used for... in my project'
>
> Being very experienced Igniter you probably know real life usage examples.
> And I appreciate if you or somebody else in community could share it.
>
> Sincerely,
> Dmitriy Pavlov
>
> пт, 27 июл. 2018 г. в 1:04, Dmitriy Setrakyan <dsetrakyan@apache.org>:
>
> > Guys,
> >
> > I just want to make sure we are all on the same page. The main use case
> for
> > LOCAL caches is to have a local hash map querable with SQL and
> > automatically persisted to a 3rd party DB.
> >
> > I want to discourage people from saying "nobody needs some feature". None
> > of the people in this discussion are users of any features - we are all
> > developers of the features. Instead of guessing whether to deprecate
> > something or not, I would actually see if it is even worth a discussion.
> > How much effort is required to fix the bug found in the LOCAL cache?
> >
> > D.
> >
> > On Thu, Jul 26, 2018 at 12:19 PM, Dmitry Pavlov <dpavlov.spb@gmail.com>
> > wrote:
> >
> > > Hi Alexey,
> > >
> > > There is nothing to be sorry about :) Сommunity appreciates an
> > alternative
> > > vision, this allows us to make as informed decisions as it possible.
> > >
> > > Thank you for finding this fact, it is very interesting.
> > >
> > > I'm not sure all these examples were prepared by experienced Ignite
> > users.
> > > So idea of deprecation may have one more argument. Deprecation will
> help
> > us
> > > to inform users about LOCAL cache: Probably local cache is not what
> they
> > > need.
> > >
> > > Sincerely,
> > > Dmitriy Pavlov
> > >
> > > чт, 26 июл. 2018 г. в 16:57, Alexey Zinoviev <zaleslaw.sin@gmail.com>:
> > >
> > > > Sorry, guys, I'll put my 1 cent
> > > >
> > > > I'd like this idea  "Implement LOCAL caches as PARTITIONED caches
> over
> > > the
> > > > local node."
> > > > It make sense for examples/testing in pseudo-distributed mode and so
> > far.
> > > >
> > > > But I think that the deprecation based on user-list mentions is a
> wrong
> > > > way. Please look here
> > > >
> https://github.com/search?q=%22CacheMode.LOCAL%22+%26+ignite&type=Code
> > > > There a lot of hello world examples with LOCAL mode.
> > > >
> > > > And of course, we can ask about that on user-list, not here, to vote
> > for
> > > > the deprecation like this.
> > > >
> > > > 2018-07-26 11:23 GMT+03:00 Vladimir Ozerov <vozerov@gridgain.com>:
> > > >
> > > > > I meant LOCAL + non-LOCAL transactions of course.
> > > > >
> > > > > On Wed, Jul 25, 2018 at 10:42 PM Dmitriy Setrakyan <
> > > > dsetrakyan@apache.org>
> > > > > wrote:
> > > > >
> > > > > > Vladimir,
> > > > > >
> > > > > > Are you suggesting that a user cannot span more than one local
> > cache
> > > > in a
> > > > > > cross cache LOCAL transactions. This is extremely surprising
to
> me,
> > > as
> > > > it
> > > > > > would require almost no effort to support it. As far as mixing
> the
> > > > local
> > > > > > caches with distributed caches, then I agree, cross-cache
> > > transactions
> > > > do
> > > > > > not make sense.
> > > > > >
> > > > > > I am not sure why deprecating local caches has become a pressing
> > > > issue. I
> > > > > > can see that there are a few bugs, but why not just fix them
and
> > move
> > > > on?
> > > > > > Can someone explain why supporting LOCAL caches is such a burden?
> > > > > >
> > > > > > Having said that, I am not completely opposed to deprecating
> LOCAL
> > > > > caches.
> > > > > > I just want to know why.
> > > > > >
> > > > > > D.
> > > > > >
> > > > > > On Wed, Jul 25, 2018 at 10:55 AM, Vladimir Ozerov <
> > > > vozerov@gridgain.com>
> > > > > > wrote:
> > > > > >
> > > > > > > Dima,
> > > > > > >
> > > > > > > LOCAL cache adds very little value to the product. It doesn't
> > > support
> > > > > > > cross-cache transactions, consumes a lot of memory, much
slower
> > > than
> > > > > any
> > > > > > > widely-used concurrent hash map. Let's go the same way
as Java
> -
> > > mark
> > > > > > LOCAL
> > > > > > > cache as "deprecated for removal", and then remove it in
3.0.
> > > > > > >
> > > > > > > On Wed, Jul 25, 2018 at 12:10 PM Dmitrii Ryabov <
> > > > somefireone@gmail.com
> > > > > >
> > > > > > > wrote:
> > > > > > >
> > > > > > > > +1 to make LOCAL as filtered PARTITIONED cache. I
think it
> > would
> > > be
> > > > > > much
> > > > > > > > easier and faster than fixing all bugs.
> > > > > > > >
> > > > > > > > 2018-07-25 11:51 GMT+03:00 Dmitriy Setrakyan <
> > > > dsetrakyan@apache.org
> > > > > >:
> > > > > > > >
> > > > > > > > > I would stay away from deprecating such huge
pieces as a
> > whole
> > > > > LOCAL
> > > > > > > > cache.
> > > > > > > > > In retrospect, we should probably not even have
LOCAL
> caches,
> > > but
> > > > > > now I
> > > > > > > > am
> > > > > > > > > certain that it is used by many users.
> > > > > > > > >
> > > > > > > > > I would do one of the following, whichever one
is easier:
> > > > > > > > >
> > > > > > > > >    - Fix the issues found with LOCAL caches,
including
> > > > persistence
> > > > > > > > support
> > > > > > > > >    - Implement LOCAL caches as PARTITIONED caches
over the
> > > local
> > > > > > node.
> > > > > > > In
> > > > > > > > >    this case, we would have to hide any
> distribution-related
> > > > config
> > > > > > > from
> > > > > > > > >    users, like affinity function, for example.
> > > > > > > > >
> > > > > > > > > D.
> > > > > > > > >
> > > > > > > > > On Wed, Jul 25, 2018 at 9:05 AM, Valentin Kulichenko
<
> > > > > > > > > valentin.kulichenko@gmail.com> wrote:
> > > > > > > > >
> > > > > > > > > > It sounds like the main drawback of LOCAL
cache is that
> > it's
> > > > > > > > implemented
> > > > > > > > > > separately and therefore has to be maintained
separately.
> > If
> > > > > that's
> > > > > > > the
> > > > > > > > > > only issue, why not keep LOCAL cache mode
on public API,
> > but
> > > > > > > implement
> > > > > > > > it
> > > > > > > > > > as a PARTITIONED cache with a node filter
forcefully set?
> > > > That's
> > > > > > > > similar
> > > > > > > > > to
> > > > > > > > > > what we do with REPLICATED caches which
are actually
> > > > PARTITIONED
> > > > > > with
> > > > > > > > > > infinite number of backups.
> > > > > > > > > >
> > > > > > > > > > This way we fix the issues described by
Stan and don't
> have
> > > to
> > > > > > > > deprecate
> > > > > > > > > > anything.
> > > > > > > > > >
> > > > > > > > > > -Val
> > > > > > > > > >
> > > > > > > > > > On Wed, Jul 25, 2018 at 12:53 AM Stanislav
Lukyanov <
> > > > > > > > > > stanlukyanov@gmail.com>
> > > > > > > > > > wrote:
> > > > > > > > > >
> > > > > > > > > > > Hi Igniters,
> > > > > > > > > > >
> > > > > > > > > > > I’d like to start a discussion about
the deprecation of
> > the
> > > > > LOCAL
> > > > > > > > > caches.
> > > > > > > > > > >
> > > > > > > > > > > LOCAL caches are an edge-case functionality
> > > > > > > > > > > I haven’t done any formal analysis,
but from my
> > experience
> > > > > LOCAL
> > > > > > > > caches
> > > > > > > > > > > are needed very rarely, if ever.
> > > > > > > > > > > I think most usages of LOCAL caches
I’ve seen were
> > misuses:
> > > > the
> > > > > > > users
> > > > > > > > > > > actually needed a simple HashMap, or
an actual
> > PARTITIONED
> > > > > cache.
> > > > > > > > > > >
> > > > > > > > > > > LOCAL caches are easy to implement
on top of
> PARTITIONED
> > > > > > > > > > > If one requires a LOCAL cache (which
is itself
> > > questionable,
> > > > as
> > > > > > > > > discussed
> > > > > > > > > > > above) it is quite easy to implement
one on top of
> > > > PARTITIONED
> > > > > > > cache.
> > > > > > > > > > > A node filter of form `node -> node.id
> > > > ().equals(localNodeId)`
> > > > > is
> > > > > > > > > enough
> > > > > > > > > > > to make the cache to be stored on the
node that created
> > it.
> > > > > > > > > > > Locality of access to the cache (i.e.
making it
> > unavailable
> > > > > from
> > > > > > > > other
> > > > > > > > > > > nodes) can be achieved on the application
level.
> > > > > > > > > > >
> > > > > > > > > > > LOCAL caches are hard to maintain
> > > > > > > > > > > A quick look at the open issues mentioning
“local
> cache”
> > > > > suggests
> > > > > > > > that
> > > > > > > > > > > this is a corner case for implementation
of many Ignite
> > > > > features:
> > > > > > > > > > >
> > > > > > > > > > >
> https://issues.apache.org/jira/issues/?jql=text%20~%20%
> > > > > > > > > > 22local%20cache%22%20and%20%20project%20%3D%20IGNITE%
> > > > > > > > > > 20and%20status%20%3D%20open
> > > > > > > > > > > In particular, a recent SO question
brought up the fact
> > > that
> > > > > > LOCAL
> > > > > > > > > caches
> > > > > > > > > > > don’t support native persistence:
> > > > > > > > > > >
> > > > > > > > > > > https://stackoverflow.com/questions/51511892/how-to-
> > > > > > > > > > configure-persistent-storage-for-apache-ignite-cache
> > > > > > > > > > > Having to ask ourselves “how does
it play with LOCAL
> > > caches”
> > > > > > every
> > > > > > > > time
> > > > > > > > > > we
> > > > > > > > > > > write any code in Ignite seems way
to much for the
> > benefits
> > > > we
> > > > > > gain
> > > > > > > > > from
> > > > > > > > > > it.
> > > > > > > > > > >
> > > > > > > > > > > Proposal
> > > > > > > > > > > Let’s deprecate LOCAL caches in 2.x
and remove them in
> > 3.0.
> > > > > > > > > > > As a part of deprecation let’s do
the following:
> > > > > > > > > > > - Put @Deprecated on the CacheMode.LOCAL
> > > > > > > > > > > - Print a warning every time a LOCAL
cache is created
> > > > > > > > > > > - Remove all mentions of LOCAL caches
from readme.io,
> if
> > > > any,
> > > > > > > except
> > > > > > > > > for
> > > > > > > > > > > the page about cache modes
> > > > > > > > > > > - On the page about cache modes explain
that LOCAL is
> > > > > deprecated
> > > > > > > and
> > > > > > > > > can
> > > > > > > > > > > be replaced with a PARTITIONED cache
with a node filter
> > > > > > > > > > >
> > > > > > > > > > > Thanks,
> > > > > > > > > > > Stan
> > > > > > > > > > >
> > > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>

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