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Apache Solr 1.2 released
Posted on: June 19, 2007 at 12:00 AM

Solr is a standalone enterprise full text search engine. It is a high performance search server with a web-services like API.

Apache Solr 1.2 released

Welcome to Apache solr 1.2 ! To get started, I would like to introduce Solr to you. Solr is a standalone enterprise full text search engine. It is a high performance search server with a web-services like API. It is based on on Lucene, with XML/HTTP and JSON APIs, hit highlighting, faceted search, caching, replication, and a Web administration interface. It is written in Java5, and easily extensible through plugins written in Java. Documents are added to a search collection via XML over HTTP. The collection is queried via HTTP to receive an XML response (or alternately JSON, Python or Ruby text formats). More precisely,

Solr offers faceted searching, hit highlighting
Optimized for High Volume Web Traffic
Flexible and Adaptable with XML configuration
Loose schema to define types and fields
Extensive caching
Extensible open architecture
XML/HTTP Interfaces
Web administration interface
Index replication
Advanced Full-Text Search Capabilities
Extensible Plugin Architecture
Flexible and Adaptable with XML configuration
Scalability - Efficient Replication to other Solr Search Servers

Before proceeding any further, let me tell you about Lucene.

Is is a full text search library.
It searches for the documents via Indexsearcher
Add documents to Index via IndexWriter
Scoring: tf* idf* lengthNorm

Solr's history
Solr was first developed at CNET Networks. Solr steadily accumulated features and attracted a robust community of users, contributors, and committers during its incubation period, which ended in January 2007. It has been donated to the Apache Software Foundation in early 2006. Solr is now a subproject of Lucene, which is Apache's Java-based full-text search engine library.
Now a days users expect high-quality search results like Google that help them find what they're looking for quickly and easily. These search engines are scalable, highly available, easy-to-maintain that doesn't cost a fortune to install. Well Apache Solr is one of them. It is an open source, Lucene Java-based search server that is easy to incorporate into your Web applications. Furthermore, it is impressive, it has a vibrant developer community that you can call on for help if you need it.

Architecture

Solr Uses and extends the Lucene Search Library. In Solr and Lucene, an index is built of one or more Documents. A Document consists of one or more Fields. A Field consists of a name, content, and metadata telling Solr how to handle the content. For instance, Fields can contain strings, numbers, boolean, or dates, as well as any types you wish to add. A Field can be described using a number of options that tell Solr how to treat the content during indexing and searching.

A Real Data Schema, with Numeric Types, Dynamic Fields, Unique Keys
Powerful Extensions to the Lucene Query Language
Support for Dynamic Faceted Browsing and Filtering
Advanced, Configurable Text Analysis
Highly Configurable and User Extensible Caching
Performance Optimizations
External Configuration via XML
An Administration Interface
Monitorable Logging
Fast Incremental Updates and Snapshot Distribution
XML and CSV/delimited-text update formats

Following are some of the features of Apache Solr:

Schema

It can drive more intelligent processing
Declarative Lucene Analyzer specification
Defines the field types and fields of documents
Explicit types eliminates the need for guessing types of fields
Dynamic Fields enables on-the-fly addition of new fields

Query

Advanced DisMax query parser for high relevancy results from user-entered queries
Highlighted context snippets
Faceted Searching based on unique field values and explicit queries
HTTP interface with configurable response formats (XML/XSLT, JSON, Python, Ruby)
Sort by any number of fields
Constant scoring range and prefix queries - no idf, coord, or lengthNorm factors, and no restriction on the number of terms the query matches.
Function Query - influence the score by a function of a field's numeric value or ordinal.

Core

Correct handling of numeric types for both sorting and range queries
Ability to control where docs with the sort field missing will be placed
Batches updates and deletes for high performance
Pluggable query handlers and extensible XML data format
Document uniqueness enforcement based on unique key field
User configurable commands triggered on index changes
Searcher concurrency control

Caching

Configurable Query Result, Filter, and Document cache instances
Fast/small filter implementation
User level caching with autowarming support
Cache warming in background
* When a new searcher is opened, configurable searches are run against it in order to warm it up to avoid slow first hits. During warming, the current searcher handles live requests.
Autowarming in background
* The most recently accessed items in the caches of the current searcher are re-populated in the new searcher, enabing high cache hit rates across index/searcher changes.
Pluggable Cache implementations

Replication

Efficient distribution of index parts that have changed via rsync transport
Configurable distribution interval allows tradeoff between timeliness and cache utilization
Pull strategy allows for easy addition of searchers

Admin Interface

Text analysis debugger, showing result of every stage in an analyzer
Web Query Interface w/ debugging output
* parsed query output
* Lucene explain() document score detailing
* explain score for documents outside of the requested range to debug why a given document wasn't ranked higher.
Comprehensive statistics on cache utilization, updates, and queries

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