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Lucene

Lucene FullText Index

In addition to the standard FullText Index, which uses the SB-Tree index algorithm, you can also create FullText indexes using the Lucene Engine. Beginning from version 2.0, this plugin is packaged with OrientDB distribution.

Syntax:

orientdb> CREATE INDEX  ON  (prop-names) FULLTEXT ENGINE LUCENE

The following SQL statement will create a FullText index on the property name for the class City, using the Lucene Engine.

orientdb> CREATE INDEX City.name ON City(name) FULLTEXT ENGINE LUCENE

Indexes can also be created on n-properties. For example, create an index on the properties name and description on the class City.

orientdb> CREATE INDEX City.name_description ON City(name, description)
          FULLTEXT ENGINE LUCENE

The default analyzer used by OrientDB when a Lucene index is created id the StandardAnalyzer.

Analyzer

In addition to the StandardAnalyzer, full text indexes can be configured to use different analyzer by the METADATA operator through CREATE INDEX.

Configure the index on City.name to use the EnglishAnalyzer:

orientdb> CREATE INDEX City.name ON City(name)
            FULLTEXT ENGINE LUCENE METADATA {
                "analyzer": "org.apache.lucene.analysis.en.EnglishAnalyzer"
            }

Configure the index on City.name to use different analyzers for indexing and querying.

orientdb> CREATE INDEX City.name ON City(name)
            FULLTEXT ENGINE LUCENE METADATA {
                "index": "org.apache.lucene.analysis.en.EnglishAnalyzer",
                "query": "org.apache.lucene.analysis.standard.StandardAnalyzer"
          }

EnglishAnalyzer will be used to analyze text while indexing and the StandardAnalyzer will be used to analyze query terms.

A very detailed configuration, on multi-field index configuration, could be:

orientdb> CREATE INDEX City.name_description ON City(name, lyrics, title,author, description)
            FULLTEXT ENGINE LUCENE METADATA {
                "default": "org.apache.lucene.analysis.standard.StandardAnalyzer",
                "index": "org.apache.lucene.analysis.core.KeywordAnalyzer",
                "query": "org.apache.lucene.analysis.standard.StandardAnalyzer",
                "name_index": "org.apache.lucene.analysis.standard.StandardAnalyzer",
                "name_query": "org.apache.lucene.analysis.core.KeywordAnalyzer",
                "lyrics_index": "org.apache.lucene.analysis.en.EnglishAnalyzer",
                "title_index": "org.apache.lucene.analysis.en.EnglishAnalyzer",
                "title_query": "org.apache.lucene.analysis.en.EnglishAnalyzer",
                "author_query": "org.apache.lucene.analysis.core.KeywordAnalyzer",
                "description_index": "org.apache.lucene.analysis.standard.StandardAnalyzer",
                "description_index_stopwords": [
                  "the",
                  "is"
                ]
            }

With this configuration, the underlying Lucene index will works in different way on each field:

  • name: indexed with StandardAnalyzer, searched with KeywordAnalyzer (it's a strange choice, but possible)
  • lyrics: indexed with EnglishAnalyzer, searched with default query analyzer StandardAnalyzer
  • title: indexed and searched with EnglishAnalyzer
  • author: indexed and searched with KeywordhAnalyzer
  • description: indexed with StandardAnalyzer with a given set of stopwords

Java API

The FullText Index with the Lucene Engine is configurable through the Java API.


    OSchema schema = databaseDocumentTx.getMetadata().getSchema();
    OClass oClass = schema.createClass("Foo");
    oClass.createProperty("name", OType.STRING);
    oClass.createIndex("City.name", "FULLTEXT", null, null, "LUCENE", new String[] { "name"});

Query parser

It is possible to configure some behavior of the Lucene query parser

Allow Leading Wildcard

Lucene by default doesn't support leading wildcard: Lucene wildcard support

It is possible to override this behavior with a dedicated flag on meta-data:

{
  "allowLeadingWildcard": true
}

Use this flag carefully, as stated in the Lucene FAQ:

Note that this can be an expensive operation: it requires scanning the list of tokens in the index in its entirety to look for those that match the pattern.

Disable lower case on terms

Lucene's QueryParser applies a lower case filter on expanded queries by default. It is possible to override this behavior with a dedicated flag on meta-data:

{
  "lowercaseExpandedTerms": false
}

It is useful when used in pair with keyword analyzer:

{
  "lowercaseExpandedTerms": false,
  "default" : "org.apache.lucene.analysis.core.KeywordAnalyzer"
}

With lowercaseExpandedTerms set to false, these two queries will return different results:

SELECT from Person WHERE name LUCENE "NAME"

SELECT from Person WHERE name LUCENE "name"

Lucene Writer fine tuning (expert)

It is possible to fine tune the behaviour of the underlying Lucene's IndexWriter

CREATE INDEX City.name ON City(name)
    FULLTEXT ENGINE LUCENE METADATA {
        "directory_type": "nio",
        "use_compound_file": false,
        "ram_buffer_MB": "16",
        "max_buffered_docs": "-1",
        "max_buffered_delete_terms": "-1",
        "ram_per_thread_MB": "1024",
        "default": "org.apache.lucene.analysis.standard.StandardAnalyzer"
    }
  • directory_type: configure the acces type to the Lucene's index
    • nio (default): the index is opened with NIOFSDirectory
    • mmap: the index is opened with MMapDirectory
    • ram: index will be created in memory with RAMDirectory
  • use_compound_file: default is false
  • ram_buffer_MB: size of the document's buffer in MB, default value is 16 MB (which means flush when buffered docs consume approximately 16 MB RAM)
  • max_buffered_docs: size of the document's buffer in number of docs, disabled by default (because IndexWriter flushes by RAM usage by default)
  • max_buffered_delete_terms: disabled by default (because IndexWriter flushes by RAM usage by default).
  • ram_per_thread_MB: default value is 1945

For a detailed explanation of config parameters and IndexWriter behaviour

Querying Lucene FullText Indexes

You can query the Lucene FullText Index using the custom operator LUCENE with the Query Parser Syntax from the Lucene Engine.

orientdb> SELECT FROM V WHERE name LUCENE "test*"

This query searches for test, tests, tester, and so on from the property name of the class V. The query can use proximity operator ~, the required (+) and prohibit (-) operators, phrase queries, regexp queries:

orientdb> SELECT FROM Article WHERE content LUCENE "(+graph -rdbms) AND +cloud"

Working with multiple fields

In addition to the standard Lucene query above, you can also query multiple fields. For example,

orientdb> SELECT FROM Class WHERE [prop1, prop2] LUCENE "query"

In this case, if the word query is a plain string, the engine parses the query using MultiFieldQueryParser on each indexed field.

To execute a more complex query on each field, surround your query with parentheses, which causes the query to address specific fields.

orientdb> SELECT FROM Article WHERE [content, author] LUCENE "(content:graph AND author:john)"

Here, the engine parses the query using the QueryParser

Numeric and date range queries

If the index is defined over a numeric field (INTEGER, LONG, DOUBLE) or a date field (DATE, DATETIME), the engine supports range queries Suppose to have a City class witha multi-field Lucene index defined:

orientdb> 
CREATE CLASS CITY EXTENDS V
CREATE PROPERTY CITY.name STRING
CREATE PROPERTY CITY.size INTEGER
CREATE INDEX City.name ON City(name,size) FULLTEXT ENGINE LUCENE

Then query using ranges:

orientdb> 
SELECT FROM City WHERE [name,size] LUCENE 'name:cas* AND size:[15000 TO 20000]'

Ranges can be applied to DATE/DATETIME field as well. Create a Lucene index over a property:

orientdb> 
CREATE CLASS Article EXTENDS V
CREATE PROPERTY Article.createdAt DATETIME
CREATE INDEX Article.createdAt  ON Article(createdAt) FULLTEXT ENGINE LUCENE

Then query to retrieve articles published only in a given time range:

orientdb> 
SELECT FROM Article WHERE createdAt LUCENE '[201612221000 TO 201612221100]'

Retrieve the Score

When the lucene index is used in a query, the results set carries a context variable for each record representing the score. To display the score add $score in projections.

SELECT *,$score FROM V WHERE name LUCENE "test*"

Creating a Manual Lucene Index

The Lucene Engine supports index creation without the need for a class.

Syntax:

CREATE INDEX <name> FULLTEXT ENGINE LUCENE  [<key-type>] [METADATA {<metadata>}]

For example, create a manual index using the CREATE INDEX command:

orientdb> CREATE INDEX Manual FULLTEXT ENGINE LUCENE STRING, STRING

Once you have created the index Manual, you can insert values in index using the INSERT INTO INDEX:... command.

orientdb> INSERT INTO INDEX:Manual (key, rid) VALUES(['Enrico', 'Rome'], #5:0)

You can then query the index through SELECT...FROM INDEX::

orientdb> SELECT FROM INDEX:Manual WHERE key LUCENE "Enrico"

Manual indexes could be created programmatically using the Java API

ODocument meta = new ODocument().field("analyzer", StandardAnalyzer.class.getName());
OIndex<?> index = databaseDocumentTx.getMetadata().getIndexManager()
        .createIndex("apiManual", OClass.INDEX_TYPE.FULLTEXT.toString(),
            new OSimpleKeyIndexDefinition(1, OType.STRING, OType.STRING), null, null, meta, OLuceneIndexFactory.LUCENE_ALGORITHM);