What are shards in Solr?

Solr sharding involves splitting a single Solr index into multiple parts, which may be on different machines. When the data is too large for one node, you can break it up and store it in sections by creating one or more shards, each containing a unique slice of the index.

What is shard in search?

A database shard, or simply a shard, is a horizontal partition of data in a database or search engine. Each shard is held on a separate database server instance, to spread load. Each shard (or server) acts as the single source for this subset of data.

What are shards and replicas in Solr?

Collection − A cluster has a logical index that is known as a collection. Shard − A shard is portion of the collection which has one or more replicas of the index. Replica − In Solr Core, a copy of shard that runs in a node is known as a replica.

How many shards are there in Solr?

Best Practice: Use one shard! Shards disable Managed Solr’s backup features. (Custom backups can be arranged for premium customers.) If your index can fit comfortably on one server, then use one shard. This is Solr’s default behavior.

What is replica in Solr?

Replica: One copy of a shard. Each replica exists within Solr as a core. A collection named “test” created with numShards=1 and replicationFactor set to two will have exactly two replicas, so there will be two cores, each on a different machine (or Solr instance).

What is collection in Solr?

Collection is a logical index spread across multiple servers. Core is that part of server which runs one collection. In non-distributed search, Single server running the Solr can have multiple collections and each of those collection is also a core. So collection and core are same if search is not distributed.

Why would you shard a database?

Sharding is necessary if a dataset is too large to be stored in a single database. Moreover, many sharding strategies allow additional machines to be added. Sharding allows a database cluster to scale along with its data and traffic growth. Sharding is also referred as horizontal partitioning.

What is a primary shard?

Each database in a sharded cluster has a primary shard that holds all the un-sharded collections for that database. The primary shard has no relation to the primary in a replica set. The mongos selects the primary shard when creating a new database by picking the shard in the cluster that has the least amount of data.

What is a Solr replica?

Solr replication uses the master-slave model to distribute complete copies of a master index to one or more slave servers. The master server receives all updates and all changes are made against a single master server.

What is SolrCloud?

SolrCloud is a flexible distributed search and indexing, without a master node to allocate nodes, shards, and replicas. Instead, Solr uses ZooKeeper to manage these locations, depending on configuration files and schemas. Queries and updates can be sent to any server.

What is core and collection in Solr?

What is SolrCloud mode?

SolrCloud mode offers index replication, failover, load balancing, and distributed queries with the help of ZooKeeper and other specialized features in Solr.

What does a request handler do in Solr?

A request handler processes requests coming to Solr. These might be query requests or index update requests. You will likely need several of these defined, depending on how you want Solr to handle the various requests you will make. A search component is a feature of search, such as highlighting or faceting.

How does distributed indexing work in Apache Solr?

All replicas of a shard are consistent, even if the updates arrive in a different order on different replicas. When not using SolrCloud, it is up to you to get all your documents indexed on each shard of your server farm. Solr supports distributed indexing (routing) in its true form only in the SolrCloud mode.

What are the features of SolrCloud for distributed search?

SolrCloud provides for a truly distributed set of features with support for things like automatic routing, leader election, optimistic concurrency and other sanity checks that are expected out of a distributed system. Everything on this page is specific to legacy setup of distributed search.