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From Dmitriy Setrakyan <dsetrak...@apache.org>
Subject Re: Deprecating LOCAL cache
Date Wed, 25 Jul 2018 08:51:13 GMT
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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