Scanned through the PR and read some of this thread. I likely have missed much other discussion, so forgive me if I'm dredging up somethings that are already discussed elsewhere.
The idea of designing the interfaces defining what information is available seems good here, but I worry that it's too auto-scaling focused. In my imagination, I would see solr having a standard informational interface that is useful to any plugin of any sort. Autoscaling should be leveraging that and we should be enhancing that to enable autoscaling. The current state of the system is one key type of information, but another type of information that should exist within solr and be exposed to plugins (including autoscaling) is events. When a new node joins there should be an event for example so that plugins can listen for that rather than incessantly polling and comparing the list of 100 nodes to a cached list of 100 nodes. In the PR I see a bunch of classes all off in a separate package, which looks like an autoscaling fiefdom which will be tempted if not forced to duplicate lots of stuff relative to other plugins and/or core. As a side note I would think the metrics system could be a plugin that leverages the same set of informational interfaces.... So there should be 3 parts to this as I imagine it. 1) Enhancements to the **plugin system** that make information about the cluster available solr to ALL plugins 2) Enhancements to the **plugin system** API's provided to ALL plugins that allow them to mutate solr safely. 3) A plugin that we intend to support for our users currently using auto scaling utilizes the enhanced information to provide a similar level of functionality as is *promised* by our current documentation of autoscaling, there might be some gaps or differences but we should be discussing what they are and providing recommended workarounds for users that relied on those promises to the users. Even if there were cases where we failed to deliver, if there were at least some conditions under which we could deliver the promised functionality those should be supported. Only if we never were able to deliver and it never worked under any circumstance should we rip stuff out entirely. Implicit in the above is the concept that there should be a facade between plugins and the core of solr. WRT #1 which will necessarily involve information collected from remote nodes, we need to be designing that thinking about what informational guarantees it provides. Latency, consistency, delivery, etc. We also need to think about what is exposed in a read-only fashion vs what plugins might write back to solr. Certainly there will be a lot of information that most plugins ignore, and we might consider having groupings of information and interfaces or annotations that indicate what info is provided, but the simplest default state is to just give plugins a reference to a class that they can use to drill into information about the cluster as needed. (SolrInformationBooth? ... or less tongue in cheek... enhance SolrInfoBean? ) Finally a fourth thing that occurs to me as I write is we need to consider what information one plugin might make available to the rest of the solr plugins. This might come later, and is hard because it's very hard to anticipate what info might be generated by unknown plugins in the future. So some humorous, not seriously suggested but hopefully memorable class names encapsulating the concepts: SolrInformationBooth (place to query) SolrLoudspeaker (event announcements) SolrControlLevers (mutate solr cluster) SolrPluginFacebookPage (info published by the plugin that others can watch) The "facade" provided to plugins by the plugin system should grow and expand such that more and more plugins can rely on it. This effort should grow it enough to move autoscaling onto it without dropping (much) functionality that we've previously published. -Gus On Fri, Jul 24, 2020 at 4:40 PM Jan Høydahl <jan....@cominvent.com> wrote: > Not clear to me what type of "alternative proposal" you're thinking of Jan > > > That would be the responsibility of Noble and others who have concerns to > detail - and try convince other peers. > It’s hard for me as a spectator to know whether to agree with Noble > without a clear picture of what the alternative API or approach would look > like. > I’m often a fan of loosely typed APIs since they tend to cause less > boilerplate code, but strong typing may indeed be a sound choice in this > API. > > Jan Høydahl > > 24. jul. 2020 kl. 01:44 skrev Ilan Ginzburg <ilans...@gmail.com>: > > > In my opinion we have to (and therefore will) ship at least a basic prod > ready implementation on top of the API that does simple things (not sure > about rack, but for example balance cores and disk size without co locating > replicas of same shard on same node). > Without such an implementation, I suspect adoption will be low. Moreover, > it's always a lot more friendly to start coding from a working example than > from scratch. > > Not clear to me what type of "alternative proposal" you're thinking of > Jan. Alternative API proposal? Alternative approach to replace Autoscaling? > > Ilan > > Ilan > > On Fri, Jul 24, 2020 at 12:11 AM Jan Høydahl <jan....@cominvent.com> > wrote: > >> Important discussion indeed. >> >> I don’t have time to dive deep into the PR or make up my mind whether >> there is a simpler and more future proof way of designing these APIs. But I >> understand that autoscaling is a complex beast and it is important we get >> it right. >> >> One question regarding having to write code vs config. Is the plan to >> ship some very simple light weight default placement rules ootb that gives >> 80% of users what they need with simple config, or would every user need to >> write code to e.g. spread replicas across hosts/racks? I’d be interested in >> seeing an alternative proposal laid out, perhaps not in code but with a >> design that can be compared and discussed. >> >> Jan Høydahl >> >> 23. jul. 2020 kl. 17:53 skrev Houston Putman <houstonput...@gmail.com>: >> >> >> I think this is a valid thing to discuss on the dev list, since this >> isn't just about code comments. >> It seems to me that Ilan wants to discuss the philosophy around how to >> design plugins and the interfaces in Solr which the plugins will talk to. >> This is broad and affects much more than just the Autoscaling framework. >> >> As a community & product, we have so far agreed that Solr should be >> lighter weight and additional features should live in plugins that are >> managed separately from Solr itself. >> At that point we need to think about the lifetime and support of these >> plugins. People love to refactor stuff in the solr core, which before >> plugins wasn't a large issue. >> However if we are now intending for many customers to rely on plugins, >> then we need to come up with standards and guarantees so that these plugins >> don't: >> >> - Stall people from upgrading Solr (minor or major versions) >> - Hinder the development of Solr Core >> - Cause us more headaches trying to keep multiple repos of plugins up >> to date with recent versions of Solr >> >> >> I am not completely sure where I stand right now, but this is definitely >> something that we should be thinking about when migrating all of this >> functionality to plugins. >> >> - Houston >> >> On Thu, Jul 23, 2020 at 9:27 AM Ishan Chattopadhyaya <is...@apache.org> >> wrote: >> >>> I think we should move the discussion back to the PR because it has more >>> context and inline comments are possible. Having this discussion in 4 >>> places (jira, pr, slack and dev list is very hard to keep track of). >>> >>> On Thu, 23 Jul, 2020, 5:57 pm Ilan Ginzburg, <ilans...@gmail.com> wrote: >>> >>>> [I’m moving a discussion from the PR >>>> <https://github.com/apache/lucene-solr/pull/1684> for SOLR-14613 >>>> <https://issues.apache.org/jira/browse/SOLR-14613> to the dev list for >>>> a wider audience. This is about replacing the now (in master) gone >>>> Autoscaling framework with a way for clients to write their customized >>>> placement code] >>>> >>>> It took me a long time to write this mail and it's quite long, sorry. >>>> Please anybody interested in the future of Autoscaling (not only those >>>> I cc'ed) do read it and provide feedback. Very impacting decisions have to >>>> be made now. >>>> >>>> Thanks Noble for your feedback. >>>> I believe it is important that we are aligned on what we build here, >>>> esp. at the early defining stages (now). >>>> >>>> Let me try to elaborate on your concerns and provide in general the >>>> rationale behind the approach. >>>> >>>> *> Anyone who wishes to implement this should not require to learn a >>>> lot before even getting started* >>>> For somebody who knows Solr (what is a Node, Collection, Shard, >>>> Replica) and basic notions related to Autoscaling (getting variables >>>> representing current state to make decisions), there’s not much to learn. >>>> The framework uses the same concepts, often with the same names. >>>> >>>> *> I don't believe we should have a set of interfaces that duplicate >>>> existing classes just for this functionality.* >>>> Where appropriate we can have existing classes be the implementations >>>> for these interfaces and be passed to the plugins, that would be perfectly >>>> ok. The proposal doesn’t include implementations at this stage, therefore >>>> there’s no duplication, or not yet... (we must get the interfaces right and >>>> agreed upon before implementation). If some interface methods in the >>>> proposal have a different name from equivalent methods in internal classes >>>> we plan to use, of course let's rename one or the other. >>>> >>>> Existing internal abstractions are most of the time concrete classes >>>> and not interfaces (Replica, Slice, DocCollection, ClusterState). >>>> Making these visible to contrib code living elsewhere is making future >>>> refactoring hard and contrib code will most likely end up reaching to >>>> methods it shouldn’t be using. If we define a clean set of interfaces for >>>> plugins, I wouldn’t hesitate to break external plugins that reach out to >>>> other internal Solr classes, but will make everything possible to keep the >>>> API backward compatible so existing plugins can be recompiled without >>>> change. >>>> >>>> *> 24 interfaces to do this is definitely over engineering* >>>> I don’t consider the number of classes or interfaces a metric of >>>> complexity or of engineering quality. There are sample >>>> <https://github.com/apache/lucene-solr/pull/1684/files#diff-ddbe185b5e7922b91b90dfabfc50df4c> >>>> plugin implementations to serve as a base for plugin writers (and for us >>>> defining this framework) and I believe the process is relatively simple. >>>> Trying to do the same things with existing Solr classes might prove a lot >>>> harder (but might be worth the effort for comparison purposes to make sure >>>> we agree on the approach? For example, getting sister replicas of a given >>>> replica in the proposed API is: replica.getShard() >>>> <https://github.com/apache/lucene-solr/pull/1684/files#diff-a2d49bd52fddde54bb7fd2e96238507eR27> >>>> .getReplicas() >>>> <https://github.com/apache/lucene-solr/pull/1684/files#diff-9633f5e169fa3095062451599daac213R31>. >>>> Doing so with the internal classes likely involves getting the >>>> DocCollection and Slice name from the Replica, then get the >>>> DocCollection from the cluster state, there get the Slice based on its >>>> name and finally getReplicas() from the Slice). I consider the role of >>>> this new framework is to make life as easy as possible for writing >>>> placement code and the like, make life easy for us to maintain it, make it >>>> easy to write a simulation engine (should be at least an order of magnitude >>>> simpler than the previous one), etc. >>>> >>>> An example regarding readability and number of interfaces: rather than >>>> defining an enum with runtime annotation for building its instances ( >>>> Variable.Type >>>> <https://github.com/apache/lucene-solr/blob/branch_8_6/solr/solrj/src/java/org/apache/solr/client/solrj/cloud/autoscaling/Variable.java#L98>) >>>> and then very generic access methods, the proposal defines a specific >>>> interface for each “variable type” (called properties >>>> <https://github.com/apache/lucene-solr/pull/1684/files#diff-4c0fa84354f93cb00e6643aefd00fd3c>). >>>> Rather than concatenating strings to specify the data to return from a >>>> remote node (based on snitches >>>> <https://github.com/apache/lucene-solr/blame/branch_8_6/solr/core/src/java/org/apache/solr/cloud/rule/ImplicitSnitch.java#L60>, >>>> see doc >>>> <https://lucene.apache.org/solr/guide/8_1/solrcloud-autoscaling-policy-preferences.html#node-selector>), >>>> the proposal is explicit and strongly typed (here >>>> <https://github.com/apache/lucene-solr/pull/1684/files#diff-4ec32958f54ec8e1f7e2d5ce8de331bb> >>>> example >>>> to get a specific system property from a node). This definitely does >>>> increase the number of interfaces, but reduces IMO the effort to code to >>>> these abstractions and provides a lot more compile time and IDE assistance. >>>> >>>> Goal is to hide all the boilerplate code and machinery (and to a point >>>> - complexity) in the implementations of these interfaces rather than have >>>> each plugin writer deal with the same problems. >>>> >>>> We’re moving from something that was complex and hard to read and debug >>>> yet functionally extremely rich, to something simpler for us, more >>>> demanding for users (write code rather than policy config if there's a need >>>> for new behavior) but that should not be less "expressive" in any >>>> significant way. One could even imagine reimplementing the former >>>> Autoscaling config Domain Specific Language on top of these API (maybe as a >>>> summer internship project :) >>>> >>>> *> This is a common mistake that we all do. When we design a feature we >>>> think that is the most important thing.* >>>> If by *"most important thing"* you mean investing the best reasonable >>>> effort to do things right then yes. >>>> If you mean trying to make a minor feature look more important and >>>> inflated than it is, I disagree. >>>> As a personal note, replica placement is not the aspect of SolrCloud >>>> I'm most interested in, but the first bottleneck we hit when pushing the >>>> scale of SolrCloud. I approach this with a state of mind "let's do it right >>>> and get it out of the way" to move to topics I really want to work on >>>> (around distribution in SolrCloud and the role of Overseer). Implementing >>>> Autoscaling in a way that simplifies future refactoring (or that does not >>>> make them harder than they already are) is therefore *very high* on my >>>> priority list, to support modest changes (Slice to Shard renaming) and >>>> more ambitious ones (replacing Zookeeper, removing Overseer, you name it). >>>> >>>> Thanks for reading, again sorry for the long email, but I hope this >>>> helps (at least helps the discussion), >>>> Ilan >>>> >>>> >>>> On Thu 23 Jul 2020 at 08:16, Noble Paul <notificati...@github.com> >>>> wrote: >>>> >>>>> I don't believe we should have a set of interfaces that duplicate >>>>> existing classes just for this functionality. This is a common mistake >>>>> that >>>>> we all do. When we design a feature we think that is the most important >>>>> thing. We endup over designing and over engineering things. This feature >>>>> will remain a tiny part of Solr. Anyone who wishes to implement this >>>>> should >>>>> not require to learn a lot before even getting started. Let's try to have >>>>> a >>>>> minimal set of interfaces so that people who try to implement them do not >>>>> have a huge learning cure. >>>>> >>>>> Let's try to understand the requirement >>>>> >>>>> - Solr wants a set of positions to place a few replicas >>>>> - The implementation wants to know what is the current state of >>>>> the cluster so that it can make those decisions >>>>> >>>>> 24 interfaces to do this is definitely over engineering >>>>> >>>>> — >>>>> You are receiving this because you authored the thread. >>>>> Reply to this email directly, view it on GitHub >>>>> <https://github.com/apache/lucene-solr/pull/1684#issuecomment-662837142>, >>>>> or unsubscribe >>>>> <https://github.com/notifications/unsubscribe-auth/AKIOMCFT5GU2II347GZ4HTTR47IVTANCNFSM4PC3HDKQ> >>>>> . >>>>> >>>> >>>> -- http://www.needhamsoftware.com (work) http://www.the111shift.com (play)
