On 12/16/2016 5:43 AM, Jaroslaw Rozanski wrote: > Leader is responsible for distributing update requests to replica. So > eventually all replicas have same state as leader. Not a problem. It > is more about the performance of such. If I gather correctly normal > replication happens by standard update request. Not by, say, segment > copy.
For SolrCloud, yes. The master/slave replication that existed before SolrCloud does work by copying segment files, but SolrCloud does not work that way. The old master/slave replication feature IS used by SolrCloud, but ONLY for index recovery -- copying the entire index from the leader to another replica in the event that the replica gets so far behind that it cannot be brought current by regular updates and/or the transaction log. This is also used to make new replicas. > Hence, if my understanding is correct, sending search request to > replica only, in index heavy environment, would bring no benefit. Correct, it would have no benefit. There's something else: when you send queries to SolrCloud, they do not necessarily stay on the node where you sent them. By default, multiple query requests are load balanced across the cloud, so they'll hit the leader anyway, even if you never send them to the leader. > So the question is: is there a mechanism, in SolrCloud (not legacy > master/slave set-up) to make one node take a load of indexing which > other nodes focus on searching. Indexing will always be done by all replicas, including the leader. Something to mention, although it doesn't accomplish what you're after: There is a preferLocalShards parameter that you can send with your query to keep SolrCloud from doing its load balancing *if* the query can be satisfied from local indexes. This parameter should only be used in one of the following situations: * Your query rate is very low. * You are already load balancing the requests yourself. If the preferlocalShards parameter is used in other situations, it can end up concentrating a large number of requests onto some replicas and leaving the other replicas idle. https://cwiki.apache.org/confluence/display/solr/Distributed+Requests#DistributedRequests-PreferLocalShards Thanks, Shawn
