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 >>>> >> >>
