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# Search Engine-Building with Lucene and Solr

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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

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### Search Engine-Building with Lucene and Solr

1. 1. Search Engine-Building with Lucene and Solr Kai Chan SoCal Code Camp, July 2013
2. 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. 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. 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. 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. 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. 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. 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. 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. 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. 11. Workflow Setup Indexing Search
12. 12. Workflow Setup Indexing Search
13. 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. 14. How Data Are Organized collection document document document field field field field field field field field field
15. 15. field content (e.g. "please read" or 30) name (e.g. "title" or "price") type options
16. 16. index document document document subject date from subject date from date from text text reply-to text reply-to
17. 17. index document document document subject date from title SKU price last name phone text description first name address
18. 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. 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. 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. 21. Workflow Setup Indexing Search
22. 22. Indexing - UpdateRequestHandler ● upload content or file to http://host: port/solr/update ● formats: XML, JSON, CSV
23. 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. 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. 25. Workflow Setup Indexing Search
26. 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. 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. 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. 29. Searching - Query Syntax - Term ● a term by itself: matches documents that contain that term ○ e.g. tablet
30. 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. 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. 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. 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. 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. 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. 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. 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. 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. 39. facet facet values (5 of them)
40. 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. 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. 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. 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. 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/