Deprecating something doesn’t mean an immediate impact on users. By deprecating LOCAL caches we would be saying that this functionality has limited support, has issues and will be removed *eventually*. By the time of 3.0 we’ll have a better idea about how many users are affected as they will be notified by deprecation and code warnings. If the number is higher than we anticipate, we can postpone removal until 4.0 and/or present a different solution/feature.
In any case, removal of LOCAL caches would hardly be the worst thing in 3.0 in terms of compatibility. Stan From: Dmitriy Setrakyan Sent: 25 июля 2018 г. 11:51 To: dev Subject: Re: Deprecating LOCAL cache 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.kuliche...@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 < > stanlukya...@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 > > >
