Transcript Apache_lucene

Apache Lucene
Ioan Toma
based on slides from Aaron Bannert [email protected]
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Copyright 2012 STI INNSBRUCK www.sti-innsbruck.at
What is Apache Lucene?
“Apache Lucene(TM) is a high-performance, full-featured text search
engine library written entirely in Java. It is a technology suitable for
nearly any application that requires full-text search, especially crossplatform.”
- from http://lucene.apache.org/
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Features
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Scalable, High-Performance Indexing
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over 95GB/hour on modern hardware
small RAM requirements -- only 1MB heap
incremental indexing as fast as batch indexing
index size roughly 20-30% the size of text indexed
Powerful, Accurate and Efficient Search Algorithms
– ranked searching -- best results returned first
– many powerful query types: phrase queries, wildcard queries, proximity queries, range
queries and more
– fielded searching (e.g., title, author, contents)
– date-range searching
– sorting by any field
– multiple-index searching with merged results
– allows simultaneous update and searching
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Features
• Cross-Platform Solution
– Available as Open Source software under the Apache License which
lets you use Lucene in both commercial and Open Source programs
– 100%-pure Java
– Implementations in other programming languages available that are
index-compatible
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CLucene - Lucene implementation in C++
Lucene.Net - Lucene implementation in .NET
Zend Search - Lucene implementation in the Zend Framework for PHP 5
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Ranked Searching
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Phrase Matching
Keyword Matching
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Prefer more unique terms first
Scoring and ranking takes into account the uniqueness of each term
when determining a document’s relevance score
Flexible Queries
• Phrases
“star wars”
• Wildcards
star*
• Ranges
{star-stun}
[2006-2007]
• Boolean Operators
star AND wars
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Field-specific Queries
• Field-specific queries can be used to target specific
fields in the Document Index.
• For example
title:”star wars”
AND
director:”George Lucas”
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Sorting
• Can sort any field in a Document
– For example, by Price, Release Date, Amazon Sales Rank, etc…
• By default, Lucene will sort results by their relevance
score. Sorting by any other field in a Document is also
supported.
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LUCENE INTERNALS
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Everything is a Document
• A document can represent anything textual:
– Word Document
– DVD (the textual metadata only)
– Website Member (name, ID, etc…)
• A Lucene Document need not refer to an actual file on a disk,
it could also resemble a row in a relational database.
• Developers are responsible for turning their own data
sets into Lucene Documents
• A document is seen as a list of fields, where a field has
a name an a value
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Indexes
• The unit of indexing in Lucene is a term. A term is often
a word.
• Indexes track term frequencies
• Every term maps back to a Document
• Lucene uses inverted index which allows Lucene to
quickly locate every document currently associated with
a given set up input search terms.
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Basic Indexing
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Parse different types of
documents (HTML, PDF,
Word, text files, etc.)
Extract tokens and related
info (Lucene Analyser)
Add the Document to an
Index
Lucene provide a standard
analyzer for English and latin
based languages
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Basic Searching
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Create a Query
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(eg. by parsing user input)
Open an Index
Search the Index
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Use the same Analyzer as before
Iterate through returned Documents
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Extract out needed results
Extract out result scores (if needed)
Lucene as SOA
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Design an HTTP query syntax
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GET queries
XML for results
Wrap Tomcat around core code
Write a Client Library
As it follows SOA principles, basic building blocks such
as load balancers can be deployed to quickly scale up
the capacity of the search subsystem.
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Lucene as SOA Diagram
Single-Machine Architecture
Lucene-based Application includes three components
1. Lucene Custom Client Library
2. Search Service
3. Custom Core Search Library
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LUCENE SCALABILITY
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Scalability Limits
• 3 main scalability factors:
– Query Rate
– Index Size
– Update Rate
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Query Rate Scalability
• Lucene is already fast
– Built-in caching
• Easy solution for heavy workloads:
(gives near-linear scaling)
– Add more query servers behind a load balancer
– Can grow as your traffic grows
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Lucene as SOA Diagram
High-Scale Multi-Machine Architecture
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Index Size Scalability
• Can easily handle millions of Documents
• Lucene is very commonly deployed into systems with
10s of millions of Documents.
• Main limits related to Index size that one is likely to run in
to will be disk capacity and disk I/O limits.
If you need bigger:
• Built-in multi-machine capabilities
– Can merge multiple remote indexes at query-time.
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Update Rate
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Lucene is threadsafe
– Can update and query at the same time
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I/O is limiting factor
Strategies for achieving even higher update rates:
– Vertical Split – for big workloads (Centralized Index Building)
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Build indexes apart from query service
Push updated indexes on intervals
– Horizontal Split – for huge workloads
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Split data into columns
Merge columns for queries
Columns only receive their own data for updates