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What is Apache Solr?

Apache Solr is an Open-source REST-API based search server. Solr is highly scalable, ready to deploy, search engine that can handle large volumes of text-centric data. It is essentially an HTTP wrapper around the full-text search engine called Apache Lucene.

An inverted index is a list of words where each word-entry links to the documents it is stored in. That way getting all documents for the search query "guru99" with simple 'get' operation.

In this tutorial, you will learn-

History of Apache Solr

  • 1999: Doug Cutting published Lucene
  • 2004: Solr was developed at CNET by Yonik Seeley as a part company in-house project
  • 2006: CNET publish the source code by donating it to the Apache Software Foundation
  • 2008: Solr 1.3 was released with enhanced search capabilities and performance enhancements
  • 2010: Merger of Lucene and Solr
  • 2012: Solr version 4.0 was released, with new Solr Cloud feature
  • 2016: Solr 6.0, was released which offers support for the execution of parallel SQL queries

Features of Apache Solr

Here, are Important features of Apache Solr:

  • Automatic Load Balancing
  • Standards-Based Open Interfaces – XML, JSON, and HTTP
  • Recommendations & Spell Suggestions are supported
  • Support for Auto-Completion and Geo-Spatial Search
  • Built-in Security for Authentication and Authorization
  • Allows you to perform a multilingual Keyword search
  • Autocomplete/Type-ahead Prediction
  • Batch and Streaming processing
  • Building machine-learning models are easy
  • Specially optimized for high volume web Traffic
  • Comprehensive HTML Admiration Interfaces
  • Supports both Schema and Schemaless configuration
  • Faceted Search and Filtering
  • Central Configuration For Entire Cluster

Key Terms used in Apache Solr

Key Term Description
Solr Core Solr Core can be defined as an index of texts and fields derived from all the documents. One Solr Instance may have single or multiple Solr Cores.
Core = an instance of Lucene Index + Solr configuration
Solr Instance Solr Instance is an instance a Solr running in the Java Virtual Machine (JVM). In Standalone mode, it only offers one instance whereas in cloud mode you can have one or more instances.
Indexing Indexing is a method for adding document's content to Solr Index. Apache Solr uses Apache Lucene Inverted Index technique.
Document It is a group of fields and their values. A document is a basic unit of data stored in Apache Core. One Apache core may contain one or more Documents.
Field The field is a key-value pair that stores the actual data in a Document. Key specifies the field name and value contains that Field data. A document may have a one or multiple fields. It is used by Apache Solr to index the document content.
Restful APIs To communicate with Solr, it is not necessary to have used Java programming. Instead, Apache Solr provides restful services to communicate with it. You can send documents and receive results in various file formats like JSON, XML, and CSV.
Full-text search Solr offers features for full-text search such as tokens, phrases, spell checking, auto-complete, wildcard, etc.
Admin Interface Solr offers an easy-to-use, user-friendly, feature powered, user interface. Using the interface you can perform tasks like managing logs, add, delete, update and search documents.
Text-Centric and Sorted by Relevance Apache Solr is used to search text documents, and the results are delivered according to the user's query.
Node In Solr cloud, every single instance is known as a node.
Cluster A cluster is a collection of nodes.
Collection A cluster has a logical index which is also called a collection.
Shard It is a small area of the collection which offers single or multiple replicas of the index.
Replica A replica is a copy of shard which runs in a node.
Leader It is a replica of the shard, which sends the requests of the Solr Cloud for the rest of replicas.

Apache Solr Architecture

Apache Solr compromises following components:

Query:

The query parser parses the queries which you need to pass to Solr. It verifies your query to check syntactical errors. After parsing the queries, it translates into a format which is known by Lucene.

Request Handler:

The request sends to Apache Solr are processed by the request handler. The request can be a query request or index update requests. You need to select the request handler according to your requirement. To pass a request to Solr, you need to map the handler to a specific URL end-point.

Response Writer

A response writer will generate formatted outputs for input queries. It supports various formats like XML, JSON, CSV.etc. You may have different response writers for different type of requests.

Update Handler:

When you send an update request to Apache Solr, it is run through a set of plugins, signature, logging, indexing. This process is known as update request processor. Update handler also responsible for modifications like adding or dropping filed, etc.

Apache Solr Applications

Application Usage
Intranet Portal
  • Easy access to search
  • Application launching
  • News and event notification
  • Single sign-on authentication
Federated Client
  • Simplified presentation
  • Search across all content
  • Authorized access only
  • Document viewing
Instrument Datasets
  • Optimized for scientists
  • Data dependent menus
  • Specialized grid filters
Regulatory Documents
  • Designed for researchers
  • Rich meta-data access
  • Spreadsheet exports
  • View document accelerator
Embedded in PLM Application
  • Offers better search experience than an RDBMS could provide
  • Late-binding security model
  • Document actions exposed on the toolbar

How to install Apache Solr

Step 1) Go to this link and click "Continue to Subscribe."

Step 2) Click on Accept Terms

Step 3) Wait for some time for the request to be accepted

Step 4) Refresh the page and click "Continue to Configuration "

Step 5) Keep the settings default and click "Continue to Launch."

Step 6) On the next page,

  • Keep the settings default
  • Ensure you have the pem file of the key
  • Click "Launch"

You will see this success message

Step 7) In EC2 console, note the public DNS of your instance

Step 8) To access Solr, simply use the URL

http://publicdns:8983

in our case it becomes

http://ec2-18-221-175-53.us-east-2.compute.amazonaws.com:8983

Note: If you have trouble accessing the instance, change inbound and outbound rules in your instance to allow all traffic

Elasticsearch Vs. Apache Solr

Parameters Apache Solr Elastic Search
Nature It is an open source project. Not an open-sourced project.
Static status Static in shema.xml Static in elasticsearch.yml
Format XML, CSV, JSON Only JSON
Index Can be reloaded during runtime with collection/core reload Defined during index/type creation with a REST call
Documentation It is well documented. It is badly documented.
Splitting Shards Possible Not possible

Advantages of Apache Solr

  • Helps you to reduce the amount of time taken to locate Information
  • It is fast, simple, powerful and flexible search engine
  • Helps you to make your products and services more accessible
  • Increase customer spend on a web application
  • Helps you to improve user experience on the web application to increase revenue and profit
  • Comprehensive HTML based Administration Interface
  • Flexible and Adaptable with XML configuration
  • Extensible Plugin Architecture
  • Highly Scalable, robust, fault-tolerant search engine
  • Supports Distributed, Shading, Replication, Clustering and Multi-Node Architecture

DisAdvantages of Apache Solr

  • It is not an ACID compliant Data Store
  • It is not useful as a primary data store. Only useful as Secondary Data Store
  • Not offers support for transactions and distributed transactions
  • Not support Joins and Complex Queries
  • Not optimal for Normalized Data

Summary

  • Apache Solr is an Open-source REST-API based search server
  • Apache Solr was developed at CNET by Yonik Seeley as a part company in-house project
  • Apache Solr offers features like Auto-Completion and Geo-Spatial Search
  • Solr Core, Solr Instance, Indexing, Document, Restful APIs, Full-text search, Admin Interface,etc. are some key terms used in Apache Solr
  • Query, Request handler, Request writer and update handlers are some of the important components of Apache Solr
  • Intranet Portal, Federated Client, Instrument Datasets, Regulatory Documents, Embedded in PLM Application are useful Apache Solr Applications
  • Apache Solr is well documented compares to elastic search which is badly documented
  • The biggest advantage of Apache Solr is that it helps you to reduce the amount of time taken to locate Information
  • The main drawback of this application It is not an ACID compliant Data Store

 

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