Master/slave is not just two roles, but a kind of cluster. I really don’t think “Standalone” captures the non-Cloud cluster. Nobody in Chegg would have any idea that “standalone” meant “no Zookeeper”.
I’ve never thought that master/slave accurately described the traditional replication model, but I can’t remember what terms I preferred because that was ten years ago. A master gives commands. That isn’t how Solr masters work. It is closer to how an NRT or TLOG leader works, actually. A Solr master just sits there and waits for other nodes to copy the index. wunder Walter Underwood wun...@wunderwood.org http://observer.wunderwood.org/ (my blog) > On Jun 17, 2020, at 3:03 PM, Trey Grainger <solrt...@gmail.com> wrote: > > Hi Walter, > >> In Solr Cloud, the leader knows about each follower and updates them. > Respectfully, I think you're mixing the "TYPE" of replica with the role of > the "leader" and "follower" > > In SolrCloud, only if the TYPE of a follower is NRT or TLOG does the leader > push updates those followers. > > When the TYPE of a follower is PULL, then it does not. In Standalone mode, > the type of a (currently) master would be NRT, and the type of the > (currently) slaves is always PULL. > > As such, this behavior is consistent across both SolrCloud and Standalone > mode. It is true that Standalone mode does not currently have support for > two of the replica TYPES that SolrCloud mode does, but I maintain that > leader vs. follower behavior is inconsistent here. > > Trey Grainger > Founder, Searchkernel > https://searchkernel.com > > > > On Wed, Jun 17, 2020 at 5:41 PM Walter Underwood <wun...@wunderwood.org> > wrote: > >> But they are not the same. In Solr Cloud, the leader knows about each >> follower and updates them. In standalone, the master has no idea that >> slaves exist until a replication request arrives. >> >> In Solr Cloud, the leader is elected. In standalone, that role is fixed at >> config load time. >> >> Looking ahead in my email inbox, publisher/subscriber is an excellent >> choice. >> >> wunder >> Walter Underwood >> wun...@wunderwood.org >> http://observer.wunderwood.org/ (my blog) >> >>> On Jun 17, 2020, at 2:21 PM, Trey Grainger <solrt...@gmail.com> wrote: >>> >>> I guess I don't see it as polysemous, but instead simplifying. >>> >>> In my proposal, the terms "leader" and "follower" would have the exact >> same >>> meaning in both SolrCloud and standalone mode. The only difference would >> be >>> that SolrCloud automatically manages the leaders and followers, whereas >> in >>> standalone mode you have to manage them manually (as is the case with >> most >>> things in SolrCloud vs. Standalone). >>> >>> My view is that having an entirely different set of terminology >> describing >>> the same thing is way more cognitive overhead than having consistent >>> terminology. >>> >>> Trey Grainger >>> Founder, Searchkernel >>> https://searchkernel.com >>> >>> On Wed, Jun 17, 2020 at 4:50 PM Walter Underwood <wun...@wunderwood.org> >>> wrote: >>> >>>> I strongly disagree with using the Solr Cloud leader/follower >> terminology >>>> for non-Cloud clusters. People in my company are confused enough without >>>> using polysemous terminology. >>>> >>>> “This node is the leader, but it means something different than the >> leader >>>> in this other cluster.” I’m dreading that conversation. >>>> >>>> I like “principal”. How about “clone” for the slave role? That suggests >>>> that >>>> it does not accept updates and that it is loosely-coupled, only >> depending >>>> on the state of the no-longer-called-master. >>>> >>>> Chegg has five production Solr Cloud clusters and one production >>>> master/slave >>>> cluster, so this is not a hypothetical for us. We have 100+ Solr hosts >> in >>>> production. >>>> >>>> wunder >>>> Walter Underwood >>>> wun...@wunderwood.org >>>> http://observer.wunderwood.org/ (my blog) >>>> >>>>> On Jun 17, 2020, at 1:36 PM, Trey Grainger <solrt...@gmail.com> wrote: >>>>> >>>>> Proposal: >>>>> "A Solr COLLECTION is composed of one or more SHARDS, which each have >> one >>>>> or more REPLICAS. Each replica can have a ROLE of either: >>>>> 1) A LEADER, which can process external updates for the shard >>>>> 2) A FOLLOWER, which receives updates from another replica" >>>>> >>>>> (Note: I prefer "role" but if others think it's too overloaded due to >> the >>>>> overseer role, we could replace it with "mode" or something similar) >>>>> ------------------------------------------- >>>>> >>>>> To be explicit with the above definitions: >>>>> 1) In SolrCloud, the roles of leaders and followers can dynamically >>>> change >>>>> based upon the status of the cluster. In standalone mode, they can be >>>>> changed by manual intervention. >>>>> 2) A leader does not have to have any followers (i.e. only one active >>>>> replica) >>>>> 3) Each shard always has one leader. >>>>> 4) A follower can also pull updates from another follower instead of a >>>>> leader (traditionally known as a REPEATER). A repeater is still a >>>> follower, >>>>> but would not be considered a leader because it can't process external >>>>> updates. >>>>> 5) A replica cannot be both a leader and a follower. >>>>> >>>>> In addition to the above roles, each replica can have a TYPE of one of: >>>>> 1) NRT - which can serve in the role of leader or follower >>>>> 2) TLOG - which can only serve in the role of follower >>>>> 3) PULL - which can only serve in the role of follower >>>>> >>>>> A replica's type may be changed automatically in the event that its >> role >>>>> changes. >>>>> >>>>> I think this terminology is consistent with the current Leader/Follower >>>>> usage while also being able to easily accomodate a rename of the >>>> historical >>>>> master/slave terminology without mental gymnastics or the introduction >> or >>>>> more cognitive load through new terminology. I think adopting the >>>>> Primary/Replica terminology will be incredibly confusing given the >>>> already >>>>> specific and well established meaning of "replica" within Solr. >>>>> >>>>> All the Best, >>>>> >>>>> Trey Grainger >>>>> Founder, Searchkernel >>>>> https://searchkernel.com >>>>> >>>>> >>>>> >>>>> On Wed, Jun 17, 2020 at 3:38 PM Anshum Gupta <ans...@anshumgupta.net> >>>> wrote: >>>>> >>>>>> Hi everyone, >>>>>> >>>>>> Moving a conversation that was happening on the PMC list to the public >>>>>> forum. Most of the following is just me recapping the conversation >> that >>>> has >>>>>> happened so far. >>>>>> >>>>>> Some members of the community have been discussing getting rid of the >>>>>> master/slave nomenclature from Solr. >>>>>> >>>>>> While this may require a non-trivial effort, a general consensus so >> far >>>>>> seems to be to start this process and switch over incrementally, if a >>>>>> single change ends up being too big. >>>>>> >>>>>> There have been a lot of suggestions around what the new nomenclature >>>> might >>>>>> look like, a few people don’t want to overlap the naming here with >> what >>>>>> already exists in SolrCloud i.e. leader/follower. >>>>>> >>>>>> Primary/Replica was an option that was suggested based on what other >>>>>> vendors are moving towards based on Wikipedia: >>>>>> https://en.wikipedia.org/wiki/Master/slave_(technology) >>>>>> , however there were concerns around the use of “replica” as that >>>> denotes a >>>>>> very specific concept in SolrCloud. Current terminology clearly >>>>>> differentiates the use of the traditional replication model from >>>> SolrCloud >>>>>> and reusing the names would make it difficult for that to happen. >>>>>> >>>>>> There were similar concerns around using Leader/follower. >>>>>> >>>>>> Let’s continue this conversation here while making sure that we >> converge >>>>>> without much bike-shedding. >>>>>> >>>>>> -Anshum >>>>>> >>>> >>>> >> >>
