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Get the most out of Solr search with PHP


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After a thorough overview of the main features and benefits of Apache Solr (an open source search server), the architecture of Solr and strategies to adopt it for your PHP application and data model will be presented. The main lessons learned around dealing with a mix of structured and non-structured content, multilingual aspects, tuning and the various state-of-the-art features of Solr will be shared as well

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Get the most out of Solr search with PHP

  1. Get the most out of Solr search with PHP Paul Borgermans
  2. About me ● Active in open source community for a while ● Squid Proxy server (about 15y ago) ● PHP based CMS solutions (mostly eZ Publish) ● Currently fancying : ● PHP as the master glue language for almost everything ● Apache Lucene family of projects (mainly Solr) ● NoSQL (Not only SQL) and scalable architectures ● CMS systems & all kinds of challenges in information management
  3. Outline ● Overview of Apache Solr ● How to use it with PHP (1) ● Concepts & internals ● How to use it with PHP (2) ● Miscellaneous tips ● Resources
  4. Overview of Apache Solr
  5. Solr Curriculum Vitae ● Open source Apache Lucene subproject ● Standalone, enterprise grade search server built on top of Lucene ● Lives in a Java servlet container ● Access through a REST-ful API ● HTTP ● Primary payload in requests: XML ● Other response formats: PHP, JSON, …
  6. Solr in a nutshell ● State of the art, advanced full text search and information retrieval ● Fast, scalable with native replication features ● Flexible configuration ● Document oriented storage ● Extensible (if you know a bit of Java), but usually not needed
  7. Full text search main features ● Tuneable relevancy ranking on top of internal similarity algorithms ● Highlighting ● Sorting ● Filtering ● “Drill-down” navigation (facets) ● Automatic related content ● Spell checking ● Multilingual text analysis
  8. At a glance ..
  9. Tunable relevancy ranking ● “Boosting” at index and query time ● certain types of content ● certain parts of content (“fields”) ● page-rank like if the content has relations ● Elevate request component ● predefined “pages/documents” to the top when certain keywords are entered ● With customised functions ● more recent articles ● proximity (geolocations)
  10. Filtering ● Does not influence the relevancy ● Narrows down the scope ● Very powerful: full boolean, wildcards, fuzzy, and unlimited combinations ● Ranges (dates, numbers, alphanumeric, ...) Also for implementing security!
  11. Facets ● Along the main query, “facet fields” may be defined, usually operating on meta-data: ● Type of content ● Publication year ● Keywords ● Author .... ● The result set is returned offering the number hits within each “facet” ● You can use the selected facet as a subsequent filter
  12. Facets: example
  13. Automatic related content (“More Like This”) ● Search engine determines itself which are the important terms of a page and performs a query ● All other normal features can be used ● Filtering ● Sorting ● Facets
  14. Automatic related content (“More Like This”)
  15. Spell checking ● Two possible strategies ● Dictionary look-up ● Using the indexed words itself (recommended) ● Possible “Google” approach using the “best guess” ● Search for “Grein botle“ => suggests “Green bottle” ● Let Solr return individual keyword suggestions => more client side processing required
  16. Multilingual features ● Adapted tokenizers ● Stemming (reducing words to common form) ● Reduces some spelling errors too! ● May decrease accuracy ● Different algorithms per language ● Normalisation (“latin 1 characters”) ● élève = eleve, Spaß = spass, ...
  17. Performance ● Solr employs intelligent caches ● filters ● queries ● internal indexes ● Optimized for search/retrieval ● Possible autowarming on start up ● When updates are done, caches are reconstructed on the fly in the background
  18. Performance (2) ● Replication ● master-slave for now ● works across platforms with same configuration ● no native OS features needed (or rsync) ● more cloud features under development ● Sharding (client driven)
  19. How to use it with part 1
  20. Installation of backend: 4 easy steps ● Download from and unpack ● Make sure you have a Java VM >= 1.5 ● $ java -version ● Sun/IBM recommended ● gcj won't do! ● $ java -jar start.jar ● http://localhost:8983/solr/admin
  21. Voila!
  22. PHP: the client side ● Roll your own classes ● Not difficult, it's REST after all ● Some Curl, XML, Json or native PHP array parsing ● Use existing libraries ● PECL: ● (follows ZF coding standards) ● eZ Components: ezcSearch ● PHP CMS's usually come with their own ● eZ Publish, Drupal, Symfony ...
  23. What's next? ● Getting data into Solr ● Basic searches ● Advanced requests ● But first something on the concepts and internals
  24. Concepts and internals
  25. The Solr/Lucene index ● Inverted index ● Holds a collection of “documents” ● Document ● Collection of fields ● Flexible schema! ● Unique ID (user defined) ● Solr uses a XML based config file: schema.xml
  26. Fields ● Various field types, derived from base classes ● Indexed ● contains the inverted index ● usually analyzed & tokenized ● makes it searchable and sortable ● Stored ● contains also the original content ● content can be part of the request response ● Can be multi-valued! ● opens possibilities beyond full text search
  27. Field definitions: schema.xml ● Field types ● text ● numerical ● dates ● location ● … (about 25 in total) ● Actual fields (name, definition, properties) ● Dynamic fields ● Copy fields (as aggregators)
  28. schema.xml: simple field type examples <fieldType name="string" class="solr.StrField" sortMissingLast="true" omitNorms="true"/> <!-- boolean type: "true" or "false" --> <fieldType name="boolean" class="solr.BoolField" sortMissingLast="true" omitNorms="true"/> <!-- A Trie based date field for faster date range queries and date faceting. --> <fieldType name="tdate" class="solr.TrieDateField" omitNorms="true" precisionStep="6" positionIncrementGap="0"/> <!-- A text field that only splits on whitespace for exact matching of words --> <fieldType name="text_ws" class="solr.TextField" positionIncrementGap="100"> <analyzer> <tokenizer class="solr.WhitespaceTokenizerFactory"/> </analyzer> </fieldType>
  29. schema.xml: more complex field type <!-- A general unstemmed text field - good if one does not know the language of the field --> <fieldType name="textgen" class="solr.TextField" positionIncrementGap="100"> <analyzer type="index"> <tokenizer class="solr.WhitespaceTokenizerFactory"/> <filter class="solr.StopFilterFactory" ignoreCase="true" words="stopwords.txt" enablePositionIncrements="false" /> <filter class="solr.WordDelimiterFilterFactory" generateWordParts="1" generateNumberParts="1" catenateWords="1" catenateNumbers="1" catenateAll="0" splitOnCaseChange="0"/> <filter class="solr.LowerCaseFilterFactory"/> </analyzer> <analyzer type="query"> <tokenizer class="solr.WhitespaceTokenizerFactory"/> <filter class="solr.SynonymFilterFactory" synonyms="synonyms.txt" ignoreCase="true" expand="true"/> <filter class="solr.StopFilterFactory" ignoreCase="true" words="stopwords.txt" enablePositionIncrements="true" /> <filter class="solr.WordDelimiterFilterFactory" generateWordParts="1" generateNumberParts="1" catenateWords="0" catenateNumbers="0" catenateAll="0" splitOnCaseChange="0"/> <filter class="solr.LowerCaseFilterFactory"/> </analyzer> </fieldType>
  30. Huh?
  31. Analysis ● Solr does not really search your text, but rather the terms that result from the analysis of text ● Typically a chain of ● Character filter(s) ● Tokenisation ● Filter A ● Filter B ● …
  32. Solr comes with many tokenizers and filters ● Some are language specific ● Others are very specialised ● It is very important to get this right otherwise, you may not get what you expect!
  33. Text analysis examples String Field type “text” term position 1 term position 2 iPad => i pad ipad élève. => elev PowerShot => power shot powershot Lets have a look: http://localhost:8983/solr/admin
  34. Character filters ● Used to cleanup text before tokenizing ● HTMLStripCharFilter (strips html, xml, js, css) ● MappingCharFilter (normalisation of characters, removing accents) ● Regular expression filter
  35. Tokenizers ● Convert text to tokens (terms) ● You can define only one per field/analyzer ● Examples ● WhitespaceTokenizer (splits on white space) ● StandardTokenizer ● CJK variants
  36. Additional filters ● Many possible per field/analyzer ● Many delivered with Solr out of the box ● If not enough, write a tiny bit of Java or look for contributions ● Examples ...
  37. Phonetic filters ● PhoneticFilterFactory ● “sounds like” transformations and matching ● Algorithms: ● Metaphone ● Double Metaphone ● Soundex ● Refined Soundex
  38. Reversing Filter ● Reverses the order of characters ● Use: allow “leading wildcards” ● *thing => gniht* ● A lot faster (prefixes)
  39. Synonyms ● Inject synonyms for certain terms ● Language specific ● Best used for query time analysis ● may inflate the search index too much ● decreases relevancy
  40. Stemming ● Reduce terms to their root form ● Language specific (or not relevant, CJK) ● Many specialised stemmers available ● Most european languages
  41. Copy fields ● Analysis is done differently for ● searching/filtering ● faceting/sorting ● Stemming and not stemming in different fields can increase relevance of results ● Use copy fields in schema.xml or do it client side
  42. How to use it with part I1
  43. Get the data and feed it ● Most *AMP applications have databases ● Map your data to a “document model” ● denormalization, flattening ● most DB fields can be fed unaltered, Solr takes care of the rest ● One constraint: it must be UTF-8!
  44. Snippets (1) class eZSolrDoc { function eZSolrDoc( $boost = false ) public function setBoost ( $boost = false ) public function addField ( $name, $content, $boost = false ) public function docToXML() } class eZSolr { public function addDocs ( $docs = array(), $commit = true, $optimize = false, $commitWithin = 0 ) .....
  45. Searching ● Construct a GET/POST query ● Base parameters ● “q” for query text ● “start” for offset ● “rows” for max number of results to return
  46. Searching (2) ● Additional parameters ● response format (wt) ● php = array(), json, ... ● type of search handler (qt) ● highlighting (hl.*) ● facets (f.<fieldName>.<FacetParam>=<value>) ● spellcheck (spellcheck) ● … Example: http://localhost:8983/solr/select/?q=content&version=2.2&start=0&rows=10&indent=on&wt=php
  47. Searching (3): a utility class
  48. Some more tips
  49. Indexing binary files ● Solr 1.4 includes the Apche Tika libraries ● convert about any format to plain text ● you can activate a dedicated requesthandler for it OR ● Use it standalone (command line) for integration into existing code See:
  50. Integrate legacy data ● Use the Solr Data Import Handler ● Able to index DB's directly ● define the schema to use (including possible joins) ● fire simple requests to Solr to actually index/update ● Also XML feeds, files (csv), ...
  51. Have multilingual content? ● Multi-core configuration ● Setup a dedicated Solr core per language ● Each has its own schema definitions, while you can still use common field names ● If using one index ● Use dynamic fields and create language specific analyzers for dedicate language suffixes/prefixes
  52. Resources ● Solr: wiki, mailing lists, downloads ● Free book, articles (by core Solr devs) ● Ask me ;)
  53. Thank you! Questions? email: paul dot borgermans at gmail dot com