This document discusses integrating the Apache Lucene full-text search engine with CouchDB. It begins by explaining that while CouchDB supports basic search through MapReduce indexes, implementing a full search engine would require recreating existing work. Lucene is introduced as a high-performance search library that can be used with CouchDB through the couchdb-lucene integration. The document provides examples of Lucene index design documents, querying the index, and integrating search into a Ruby on Rails application with pagination.

1. Finding stuff under the Couch
with CouchDB-Lucene
Martin Rehfeld
@ RUG-B 01-Apr-2010

2. CouchDB
• JSON document store
• all documents in a given database reside in
one large pool and may be retrieved using
their ID ...
• ... or through Map & Reduce based indexes

3. So how do you do full
text search?

4. You potentially could
achieve this with just
Map & Reduce functions

5. But that would mean
implementing an actual
search engine ...

6. ... and this has been done
before.

7. Enter Lucene
Apache Lucene 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 cross-platform.
Courtesy of The Apache Foundation

8. Lucene Features
• ranked searching
• many powerful query types: phrase queries,
wildcard queries, proximity queries, range
queries and more
• fielded searching (e.g., title, author, contents)
• boolean operators
• sorting by any field
• allows simultaneous update and searching

9. CouchDB Integration
• couchdb-lucene
(ready to run Lucene plus
CouchDB interface)
• Search interface via
http_db_handlers, usually
_fti
• Indexer interface via
CouchDB
update_notification
facility and fulltext design
docs

10. Sample design document,
i.e., _id: „_design/search“
{
"fulltext": {
"by_name": {
"defaults": { "store":"yes" },
"index":"function(doc) { var ret=new
Document(); ret.add(doc.name); return ret }"
}
}
}

11. Sample design document,
i.e., _id: „_design/search“
Name of the index
{
"fulltext": {
"by_name": {
"defaults": { "store":"yes" },
"index":"function(doc) { var ret=new
Document(); ret.add(doc.name); return ret }"
}
}
}

12. Sample design document,
i.e., _id: „_design/search“
Name of the index
{
"fulltext": { Default options
"by_name": { (can be overridden per field)
"defaults": { "store":"yes" },
"index":"function(doc) { var ret=new
Document(); ret.add(doc.name); return ret }"
}
}
}

13. Sample design document,
i.e., _id: „_design/search“
Name of the index
{
"fulltext": { Default options
"by_name": { (can be overridden per field)
"defaults": { "store":"yes" },
"index":"function(doc) { var ret=new
Document(); ret.add(doc.name); return ret }"
}
} Index function
}

14. Sample design document,
i.e., _id: „_design/search“
Name of the index
{
"fulltext": { Default options
"by_name": { (can be overridden per field)
"defaults": { "store":"yes" },
"index":"function(doc) { var ret=new
Document(); ret.add(doc.name); return ret }"
}
} Index function Builds and returns documents to
} be put into Lucene‘s index (may
return an array of multiple
documents)

15. Querying the index
http://localhost:5984/your-couch-db/_fti/
your-design-document-name/your-index-name?
q=
query string
sort=
comma-separated fields to sort on
limit=
max number of results to return
skip=
offset
include_docs=
include CouchDB documents in
response

16. A full stack example

17. CouchDB Person
Document
{
"_id": "9db68c69726e486b811859937fbb6b09",
"_rev": "1-c890039865e37eb8b911ff762162772e",
"name": "Martin Rehfeld",
"email": "martin.rehfeld@glnetworks.de",
"notes": "Talks about CouchDB Lucene"
}

18. Objectives
• Search for people by name
• Search for people by any field‘s content
• Querying from Ruby
• Paginating results

19. Index Function
function(doc) {
// first check if doc is a person document!
...
var ret=new Document();
ret.add(doc.name);
ret.add(doc.email);
ret.add(doc.notes);
ret.add(doc.name, {field:“name“, store:“yes“});
ret.add(doc.email, {field:“email“, store:“yes“});
return ret;
}

20. Index Function
function(doc) {
// first check if doc is a person document!
...
var ret=new Document();
} content added to
ret.add(doc.name);
ret.add(doc.email);
ret.add(doc.notes);
„default“ field
ret.add(doc.name, {field:“name“, store:“yes“});
ret.add(doc.email, {field:“email“, store:“yes“});
return ret;
}

21. Index Function
function(doc) {
// first check if doc is a person document!
...
var ret=new Document();
} content added to
ret.add(doc.name);
ret.add(doc.email);
ret.add(doc.notes);
„default“ field
ret.add(doc.name, {field:“name“, store:“yes“});
ret.add(doc.email, {field:“email“, store:“yes“});
return ret;
content added to
}
named fields

22. Field Options
name description available options
the field name to index
field user-defined
under
date, double, float, int, long,
type the type of the field
string
whether the data is stored.
store The value will be returned yes, no
in the search result
analyzed,
whether (and how) the data analyzed_no_norms, no,
index
is indexed not_analyzed,
not_analyzed_no_norms

23. Querying the Index I
http://localhost:5984/mydb/_fti/search/
global?q=couchdb
{
"q": "default:couchdb",
"etag": "119e498956048ea8",
"skip": 0,
"limit": 25,
"total_rows": 1,
"search_duration": 0,
"fetch_duration": 8,
"rows": [
{
"id": "9db68c69726e486b811859937fbb6b09",
"score": 4.520571708679199,
"fields": {
"name": "Martin Rehfeld",
"email": "martin.rehfeld@glnetworks.de",
}
}
]
}

24. Querying the Index I
http://localhost:5984/mydb/_fti/search/
global?q=couchdb
default field
{
"q": "default:couchdb", is queried
"etag": "119e498956048ea8",
"skip": 0,
"limit": 25,
"total_rows": 1,
"search_duration": 0,
"fetch_duration": 8,
"rows": [
{
"id": "9db68c69726e486b811859937fbb6b09",
"score": 4.520571708679199,
"fields": {
"name": "Martin Rehfeld",
"email": "martin.rehfeld@glnetworks.de",
}
}
]
}

25. Querying the Index I
http://localhost:5984/mydb/_fti/search/
global?q=couchdb
default field
{
"q": "default:couchdb", is queried Content of fields
"etag": "119e498956048ea8",
"skip": 0,
"limit": 25, with store:“yes“
"total_rows": 1,
"search_duration": 0, option are returned
"fetch_duration": 8,
"rows": [ with the query
{
results
"id": "9db68c69726e486b811859937fbb6b09",
"score": 4.520571708679199,
"fields": {
"name": "Martin Rehfeld",
"email": "martin.rehfeld@glnetworks.de",
}
}
]
}

26. Querying the Index II
http://localhost:5984/mydb/_fti/search/
global?q=name:rehfeld
{
"q": "name:rehfeld",
"etag": "119e498956048ea8",
"skip": 0,
"limit": 25,
"total_rows": 1,
"search_duration": 0,
"fetch_duration": 8,
"rows": [
{
"id": "9db68c69726e486b811859937fbb6b09",
"score": 4.520571708679199,
"fields": {
"name": "Martin Rehfeld",
"email": "martin.rehfeld@glnetworks.de",
}
}
]
}

27. Querying the Index II
http://localhost:5984/mydb/_fti/search/
global?q=name:rehfeld
{
"q": "name:rehfeld", name field
"etag": "119e498956048ea8",
"skip": 0,
"limit": 25,
is queried
"total_rows": 1,
"search_duration": 0,
"fetch_duration": 8,
"rows": [
{
"id": "9db68c69726e486b811859937fbb6b09",
"score": 4.520571708679199,
"fields": {
"name": "Martin Rehfeld",
"email": "martin.rehfeld@glnetworks.de",
}
}
]
}

28. Querying from Ruby
class Search
include HTTParty
base_uri "localhost:5984/#{CouchPotato::Config.database_name}/_fti/search"
format :json
def self.query(options = {})
index = options.delete(:index)
get("/#{index}", :query => options)
end
end

29. Controller / Pagination
class SearchController < ApplicationController
HITS_PER_PAGE = 10
def index
result = Search.query(params.merge(:skip => skip, :limit => HITS_PER_PAGE))
@hits = WillPaginate::Collection.create(params[:page] || 1, HITS_PER_PAGE,
result['total_rows']) do |pager|
pager.replace(result['rows'])
end
end
private
def skip
params[:page] ? (params[:page].to_i - 1) * HITS_PER_PAGE : 0
end
end

30. Resources
• http://couchdb.apache.org/
• http://lucene.apache.org/java/docs/index.html
• http://github.com/rnewson/couchdb-lucene
• http://lucene.apache.org/java/3_0_1/
queryparsersyntax.html

31. Q &A
!
Martin Rehfeld
http://inside.glnetworks.de
martin.rehfeld@glnetworks.de
@klickmich