| = How SolrCloud Works |
| :page-children: shards-and-indexing-data-in-solrcloud, distributed-requests, aliases |
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| |
| The following sections cover provide general information about how various SolrCloud features work. To understand these features, it's important to first understand a few key concepts that relate to SolrCloud. |
| |
| * <<shards-and-indexing-data-in-solrcloud.adoc#,Shards and Indexing Data in SolrCloud>> |
| * <<distributed-requests.adoc#,Distributed Requests>> |
| * <<aliases.adoc#,Standard and Routed Aliases>> |
| |
| If you are already familiar with SolrCloud concepts and basic functionality, you can skip to the section covering <<solrcloud-configuration-and-parameters.adoc#,SolrCloud Configuration and Parameters>>. |
| |
| == Key SolrCloud Concepts |
| |
| A SolrCloud cluster consists of some "logical" concepts layered on top of some "physical" concepts. |
| |
| === Logical Concepts |
| |
| * A Cluster can host multiple Collections of Solr Documents. |
| * A collection can be partitioned into multiple Shards, which contain a subset of the Documents in the Collection. |
| * The number of Shards that a Collection has determines: |
| ** The theoretical limit to the number of Documents that Collection can reasonably contain. |
| ** The amount of parallelization that is possible for an individual search request. |
| |
| === Physical Concepts |
| |
| * A Cluster is made up of one or more Solr Nodes, which are running instances of the Solr server process. |
| * Each Node can host multiple Cores. |
| * Each Core in a Cluster is a physical Replica for a logical Shard. |
| * Every Replica uses the same configuration specified for the Collection that it is a part of. |
| * The number of Replicas that each Shard has determines: |
| ** The level of redundancy built into the Collection and how fault tolerant the Cluster can be in the event that some Nodes become unavailable. |
| ** The theoretical limit in the number concurrent search requests that can be processed under heavy load. |
| |
| WARNING: Make sure the DNS resolution in your cluster is stable, i.e., |
| for each live host belonging to a Cluster the host name always corresponds to the |
| same specific IP and physical node. For example, in clusters deployed on AWS this would |
| require setting `preserve_hostname: true` in `/etc/cloud/cloud.cfg`. Changing DNS resolution |
| of live nodes may lead to unexpected errors. See SOLR-13159 for more details. |
