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 > >>>> > >> > >> > >
