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From Vladimir Ozerov <voze...@gridgain.com>
Subject Re: Deprecating LOCAL cache
Date Wed, 25 Jul 2018 09:55:43 GMT
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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