These are the slides for the session I presented at SoCal Code Camp San Diego on July 27, 2013. http://www.socalcodecamp.com/socalcodecamp/session.aspx?sid=6b28337d-6eae-4003-a664-5ed719f43533

1. Search Engine-Building
with Lucene and Solr
Kai Chan
SoCal Code Camp, July 2013

2. How to Search - One Approach
for each document d {
if (query is a substring of d's content) {
add d to the list of results
}
}
sort the result (or not)

3. How to Search - Problems
● slow
○ reads the whole dataset for each search
● not scalable
○ if you dataset grows by 10x,
your search slows down by 10x
● how to show the most relevant documents
first?
○ list of results can be quite long
○ users have limited time and patience

4. Inverted Index - Introduction
● like the "index" at the end of books
● a map of one of the following types
○ term → document list
○ term → <document, position> list

5. documents:
T[0] = "it is what it is"
T[1] = "what is it"
T[2] = "it is a banana"
inverted index (without positions):
"a": {2}
"banana": {2}
"is": {0, 1, 2}
"it": {0, 1, 2}
"what": {0, 1}
inverted index (with positions):
"a": {(2, 2)}
"banana": {(2, 3)}
"is": {(0, 1), (0, 4), (1, 1), (2, 1)}
"it": {(0, 0), (0, 3), (1, 2), (2, 0)}
"what": {(0, 2), (1, 0)}
Credit: Wikipedia (http://en.wikipedia.org/wiki/Inverted_index)

6. Inverted Index - Speed
● term list
○ typically very small
○ grows slowly
● term lookup
○ O(1) to O(log(number of terms))
● for a particular term
○ document lists: very small
○ document + position lists: still small
● few terms per query

7. Inverted Index - Relevance
● information in the index enables:
○ determination (scoring) of relevance of each
document to the query
○ comparison of relevance among documents
○ sorting by (decreasing) relevance
■ i.e. the most relevant document first

8. Lucene v.s. Solr - Lucene
● full-text search library
● creates, updates and read from the index
● takes queries and produces search results
● your application creates objects and calls
methods in the Lucene API
● provides building blocks for custom features

9. Lucene v.s. Solr - Solr
● full-text search server
● uses Lucene for indexing and search
● REST-like API over HTTP
● different output formats (e.g. XML, JSON)
● provides some features not built into Lucene

10. machine running Java VM
your application
machine running Java VM
servlet container (e.g. Tomcat, Jetty)
Solr
Solr code
Lucene code libraries
index
Lucene
Lucene code
index
libraries
client
HTTP
Lucene:
Solr:

11. Workflow
Setup
Indexing
Search

12. Workflow
Setup
Indexing
Search

13. Workflow - Setup
● servlet configuration
○ e.g. port number, max POST size
○ you can usually use the default settings
● Solr configuration
○ e.g. data directory, deduplication, language
identification, highlighting
○ you can usually use the default settings
● schema definition
○ defines fields in your documents
○ you can use the default settings if you name your
fields in a certain way

14. How Data Are Organized
collection
document document document
field
field
field
field
field
field
field
field
field

15. field
content (e.g. "please read" or 30)
name (e.g. "title" or "price")
type
options

16. index
document document document
subject
date
from
subject
date
from
date
from
text text
reply-to
text
reply-to

17. index
document document document
subject
date
from
title
SKU
price
last name
phone
text description
first name
address

18. Solr Field Definition
● field
○ name (e.g. "subject")
○ type (e.g. "text_general")
○ options (e.g. indexed="true" stored="true")
● field type
○ text: "string", "text_general"
○ numeric: "int", "long", "float", "double"
● options
○ indexed: content can be searched
○ stored: content can be returned at search-time
○ multivalued: multiple values per field & document

19. Solr Dynamic Field
● define field by naming convention
● "amount_i": int, index, stored
● "tag_ss": string, indexed, stored, multivalued
name type indexed stored multiValued
*_i int true true false
*_l long true true false
*_f float true true false
*_d double true true false
*_s string true true false
*_ss string true true true
*_t text_general true true false
*_txt text_general true true true

20. Solr Copy Field
● copy one or more fields into another field
● can be used to define a catch-all field
○ source: "title", "author", "description"
○ destination: "text"
○ searching the "text" field has the effect of searching
all the other three fields

21. Workflow
Setup
Indexing
Search

22. Indexing - UpdateRequestHandler
● upload content or file to http://host:
port/solr/update
● formats: XML, JSON, CSV

23. XML:
<add>
<doc>
<field name="id">apple</field>
<field name="compName">Apple</field>
<field name="address">1 Infinite Way, Cupertino CA</field>
</doc>
<doc>
<field name="id">asus</field>
<field name="compName">ASUS Computer</field>
<field name="address">800 Corporate Way Fremont, CA 94539</field>
</doc>
</add>
CSV:
id,compName_s,address_s
apple,Apple,"1 Infinite Way, Cupertino CA"
asus,Asus Computer,"800 Corporate Way Fremont, CA 94539"
JSON:
[
{"id":"apple","compName_s":"Apple","address_s":"1 Infinite Way,
Cupertino CA"}
{"id":"asus","compName_s":"Asus Computer","address_s":"800 Corporate
Way Fremont, CA 94539"}
]

24. Indexing - DataImportHandler
● has its own config file (data-config.xml)
● import data from various sources
○ RDBMS (JDBC)
○ e-mail (IMAP)
○ XML data locally (file) or remotely (HTTP)
● transformers
○ extract data (RegEx, XPath)
○ manipulate data (strip HTML tags)

25. Workflow
Setup
Indexing
Search

26. Searching - Basics
● send request to http://host:port/solr/search
● parameters
○ q - main query
○ fq - filter query
○ defType - query parser (e.g. lucene, edismax)
○ fl - fields to return
○ sort - sort criteria
○ wt - response writer (e.g. xml, json)
○ indent - set to true for pretty-printing

27. http://localhost:8983/solr/select?q=title:tablet&
fl=title,price,inStock&sort=price&wt=json
search handler's URL main query
response writersort criteriafields to return

28. Searching - Query Syntax - Field
● search a specific field
○ field_name:value
● if field omitted, Solr uses default field:
○ df parameter in URL
○ defaultSearchField setting in schema.xml
○ "text"

29. Searching - Query Syntax - Term
● a term by itself: matches documents that
contain that term
○ e.g. tablet

30. Searching - Query Syntax - Boolean
● boolean operators are supported
○ AND &&
○ OR ||
○ NOT !
● e.g. a AND b
○ all of a, b must occur
● e.g. a OR b
○ at least one of a, b must occur
● e.g. a AND NOT b
○ a must occur and b must not occur

31. Searching - Query Syntax - Boolean
● Lucene/Solr's boolean operators are not true
boolean operators
● e.g. a OR b OR c does not behave like
(a OR b) OR c
○ instead, a OR b OR c means at least one of a, b, c
must occur
● parentheses are supported

32. Searching - Query Syntax - Boolean
● "+" prefix means "must"
● "-" prefix means "must not"
● no prefix means "at least one must"
(by default)
○ e.g. a b c
■ at least one of a, b, c must occur
● operators can mix
○ e.g. +a b c d -e
■ a must occur
■ at least one of b, c, d must occur
■ e must not occur

33. Searching - Query Syntax - Phrase
● phrases are enclosed by double-quotes
● e.g. +"the phrase"
○ the phrase must occur
● e.g. -"the phrase"
○ the phrase must not occur

34. Searching - Query Syntax - Boost
● manually assign different weights to clauses
● gives more weight to a field
○ e.g. title:a^10 body:a
● gives more weight to a word
○ e.g. title:a title:b^10
● gives phrases more weight than words
○ e.g. title:(+a +b) title:"a b"^10

35. Searching - Query Syntax - Range
● matches field values within a range
○ inclusive range - denoted by square brackets
○ exclusive range - denoted by curly brackets
● e.g. age:[10 TO 20]
○ matches the field "age" with the value in 10..20
● string or numeric comparison, depending on
the field's type

36. Searching - Query Syntax - EDisMax
● suitable for user-generated queries
○ supports a subset of Lucene QP's syntax
○ does not complain about the syntax
○ searches for individual words across several fields
("disjunction")
○ uses max score of a word in all fields for scoring
("max")
● configurable (in solrconfig.xml)
○ what fields to search the words in
○ weighting of these fields

37. Sorting
● default: sorting by decreasing score
● sorting by field: using the sort parameter
○ specify field name and order
■ price asc - sort by "price" field, ascending
■ price desc - sort by "price" field, descending
○ multiple fields and orders by comma
■ starRating desc, price asc - sort by
"starRating" field, descending, and then by
"price" field, ascending
○ cannot use multivalued fields
○ overrides sorting by decreasing relevance

38. Faceted Search
● facet values: (distinct) values (generally non-
overlapping) ranges of a field
● displaying facets
○ show possible values
○ let users narrow down their searches easily

39. facet
facet values (5 of them)

40. Faceted Search
● set facet parameter to true - enables
faceting
● other parameters
○ facet.field - use the field's values as facets
■ return <value, count> pairs
○ facet.query - use the given queries as facets
■ return <query, count> pairs
○ facet.sort - set the ordering of the facets;
■ can be "count" or "index"
○ facet.offset and face.limit - used for
pagination of facets

41. Resources - Books
● Lucene in Action
○ written by 3 committer and PMC members
○ somewhat outdated (2010; covers Lucene 3.0)
○ http://www.manning.com/hatcher3/
● Solr in Action
○ early access; coming out later this year
○ http://www.manning.com/grainger/
● Apache Solr 4 Cookbook
○ common problems and useful tips
○ http://www.packtpub.com/apache-solr-4-
cookbook/book

42. Resources - Books
● Introduction to Information Retrieval
○ not specific to Lucene/Solr, but about IR concepts
○ free e-book
○ http://nlp.stanford.edu/IR-book/
● Managing Gigabytes
○ indexing, compression and other topics
○ accompanied by MG4J - a full-text search software
○ http://mg4j.di.unimi.it/

43. Resources - Web
● official websites
○ Lucene Core - http://lucene.apache.org/core/
○ Solr - http://lucene.apache.org/solr/
● mailing lists
● Wiki sites
○ Lucene Core - http://wiki.apache.org/lucene-java/
○ Solr - http://wiki.apache.org/solr/
● reference guides
○ API Documentation for Lucene and Solr
○ Apache Solr Reference Guide (LucidWorks) - http:
//lucene.apache.org/solr/tutorial.html

44. Getting Started
● download Solr
○ requires Java 6 or newer to run
● Solr comes bundled and configured with
Jetty
○ <Solr directory>/example/start.jar
● "exampledocs" directory contains sample
documents
○ <Solr directory>/example/exampledocs/post.jar
● use the Solr admin interface
○ http://localhost:8983/solr/