Talking a little out of my depth here as I haven't ben in that code, so if there are corrections they're welcome.
In general, there's nothing special between TLOG and PULL replicas in terms of query routing. For that matter, nothing special about either of these .vs. NRT replicas for _queries_. SolrCloud has internal load balancers that route queries across the network. SolrCloud automatically bypasses all non-active replicas. So there's no particular need to use a fronting load balancer. That said, it depends on how you are accessing SolrCloud. By that I mean if you provide a single HTTP end point to a single node, you have a single point of failure. Even this is irrelevant if you use SolrJ because it has (you guessed it) an internal load balancer and is ZooKeeper-aware so can handle nodes coming and going. So look at it this way. Each Solr node has a list of active replicas and directs queries (or sub-queries) to those replicas. It doesn't matter _where_ the replica is or, indeed, whether any of them are on the same node. As long as Solr is running, it sends queries to the right place. "will it automatically favour PULL replicas" No. There is so little extra work in a TLOG .vs. a PULL replica that this is minimally useful. The extra work a TLOG replica does is just to flush out the incoming documents to the tlog, a bit of I/O. Much more interesting is that the new metrics are in place to allow much more intelligent use of resources. A heavy request on a replica will put _much_ more load on that machine than handling the TLOG. The metrics will allow SolrCloud to say "replicas 1, 3, 5 are pretty busy, let's not use them for more work until they get less busy", and it won't matter whether they're TLOG, PULL or NRT replicas.. Best, Erick On Sun, Feb 11, 2018 at 6:35 PM, Greg Roodt <gro...@gmail.com> wrote: > Hi > > I have a question around how queries are routed and load-balanced in a > cluster of mixed TLOG and PULL replicas. > > I thought that I might have to put a load-balancer in front of the PULL > replicas and direct queries at them manually as nodes are added and removed > as PULL replicas. However, it seems that SolrCloud handles this > automatically? > > If I add a new PULL replica node, it goes into state="recovering" while it > pulls the core. As expected. What happens if queries are directed at this > node while in this state? From what I am observing, the query gets directed > to another node? > > If SolrCloud is handling the routing of requests to active nodes, will it > automatically favour PULL replicas for read queries and TLOG replicas for > writes? > > Thanks > Greg
