Availability: Open Source

It is used for searches of data stored in HDFS in Hadoop

It is built upon a Java library called Lucene.

Solr works with HTTP, XML. It offers application program interfaces (APIs) for Java script Object Notation (JSON), Python, and Ruby

1. Indexing: converts the documents into a machine-readable format.

2. Querying: Understanding the terms of a query posed by the user in which terms involve images, keywords, and so on.

3. Mapping: Solr maps the user query with the documents in the database to retrieve the corresponding results.

4. Ranking the outcome: ranks the outputs based on the relevance with the query by searching the indexed documents using the engine.

Highly reliable, scalable and fault tolerant

Advanced full-text search

Near real-time indexing

Standards-based open interfaces like XML, JSON and HTTP

Comprehensive HTML administration interfaces

Server statistics exposed over JMX for monitoring

Linearly scalable, auto index replication, auto failover and recovery

Flexible and adaptable, with XML configuration