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Lucene Index

Following details are applicable for Oak release 1.0.8 and earlier. For current documentation refer to Current Lucene documentation

Oak supports Lucene based indexes to support both property constraint and full text constraints

The Lucene Full-Text Index

The full-text index handles the ‘contains’ type of queries:

//*[jcr:contains(., 'text')]

If a full-text index is configured, then all queries that have a full-text condition use the full-text index, no matter if there are other conditions that are indexed, and no matter if there is a path restriction.

If no full-text index is configured, then queries with full-text conditions may not work as expected. (The query engine has a basic verification in place for full-text conditions, but it does not support all features that Lucene does, and it traverses all nodes if there are no indexed constraints).

The full-text index update is asynchronous via a background thread, see Oak#withAsyncIndexing. This means that some full-text searches will not work for a small window of time: the background thread runs every 5 seconds, plus the time is takes to run the diff and to run the text-extraction process.

The async update status is now reflected on the oak:index node with the help of a few properties, see OAK-980

TODO Node aggregation OAK-828

The index definition node for a lucene-based full-text index:

  • must be of type oak:QueryIndexDefinition
  • must have the type property set to lucene
  • must contain the async property set to the value async, this is what sends the index update process to a background thread

Optionally you can add

  • what subset of property types to be included in the index via the
    includePropertyTypes property
  • a blacklist of property names: what property to be excluded from the index via the excludePropertyNames property
  • the reindex flag which when set to true, triggers a full content re-index.

Example:

{
  NodeBuilder index = root.child("oak:index");
  index.child("lucene")
    .setProperty("jcr:primaryType", "oak:QueryIndexDefinition", Type.NAME)
    .setProperty("type", "lucene")
    .setProperty("async", "async")
    .setProperty(PropertyStates.createProperty("includePropertyTypes", ImmutableSet.of(
        PropertyType.TYPENAME_STRING, PropertyType.TYPENAME_BINARY), Type.STRINGS))
    .setProperty(PropertyStates.createProperty("excludePropertyNames", ImmutableSet.of( 
        "jcr:createdBy", "jcr:lastModifiedBy"), Type.STRINGS))
    .setProperty("reindex", true);
}

Note The Oak Lucene index will only index Strings and Binaries by default. If you need to add another data type, you need to add it to the
includePropertyTypes setting, and don’t forget to set the reindex flag to true.

Lucene Property Index (Since 1.0.8)

Oak uses Lucene for creating index to support queries which involve property constraint that is not full-text

select * from [nt:base] where [alias] = '/admin'

To define a property index on a subtree for above query you have to add an index definition

"uuid" : {
        "jcr:primaryType": "oak:QueryIndexDefinition",
        "type": "lucene",
        "async": "async",
        "fulltextEnabled": false,
        "includePropertyNames": ["alias"]
    }

The index definition node for a lucene-based full-text index:

  • must be of type oak:QueryIndexDefinition
  • must have the type property set to lucene
  • must contain the async property set to the value async, this is what sends the index update process to a background thread
  • must have fulltextEnabled set to false
  • must provide a whitelist of property names which should be indexed via includePropertyNames

Note that compared to Property Index Lucene Property Index is always configured in Async mode hence it might lag behind in reflecting the current repository state while performing the query

Taking another example.

select
    *
from
    [app:Asset] as a
where
    [jcr:content/jcr:lastModified] > cast('2014-10-01T00:00:00.000+02:00' as date)
    and [jcr:content/metadata/format] = 'image'
order by
    jcr:content/jcr:lastModified

To enable faster execution for above query you can create following Lucene property index

"assetIndex":
{
  "jcr:primaryType":"oak:QueryIndexDefinition",
  "declaringNodeTypes":"app:Asset",
  "includePropertyNames":["jcr:content/jcr:lastModified" , 
      "jcr:content/metadata/format"],
  "type":"lucene",
  "async":"async",
  "reindex":true,
  "fulltextEnabled":false,
  "orderedProps":["jcr:content/jcr:lastModified"]
  "properties":	{
    "jcr:primaryType":"oak:Unstructured",
    "jcr:content": {
      "jcr:primaryType":"oak:Unstructured",
      "jcr:lastModified":	{
        "jcr:primaryType":"oak:Unstructured",
        "type":"Date"
      }
    }
  }	
}

Above index definition makes use of various features supported by property index

  • declaringNodeTypes - As the query involves nodes of type app:Asset index is restricted to only index nodes of type app:Asset
  • orderedProps - As the query performs sorting via order by clause index is configured with property names which are used in sorting
  • properties - For ordering to work properly we need to tell the type of property

For implementation details refer to OAK-2005. Following sections would provide more details about supported features

Index Definition

Lucene index definition is managed via NodeStore and supports following attributes

type
Required and should always be lucene
async
Required and should always be async
fulltextEnabled
For Lucene based property index this should always be set to false
declaringNodeTypes
Node type names whose properties should be indexed. If not specified then all nodes would indexed if they have properties defined in includePropertyNames. For smaller and efficient indexes its recommended that declaringNodeTypes should be specified according to your query needs
includePropertyNames
List of property name which should be indexed. Property name can be relative e.g. jcr:content/jcr:lastModified
orderedProps
List of property names which would be used in the order by clause of the query
includePropertyTypes
Used in Lucene Fulltext Index
For full text index defaults to String, Binary
List of property types which should be indexed. The values can be one specified in PropertyType Names
blobSize
Default value 32768 (32kb)
Size in bytes used for splitting the index files when storing them in NodeStore
functionName
Name to be used to enable index usage with native query support

Property Definition

In some cases property specific configurations are required. For example typically while performing order by in query user does not specify the property type. In such cases you need to specify the property type explicitly.

Property definition nodes are created as per there property name under properties node of index definition node. For relative properties you would need to create the required path structure under properties node. For e.g. for property jcr:content/metadata/format you need to create property node at path <index definition node>/properties/jcr:content/jcr:lastModified

"properties":
  {
    "jcr:primaryType":"oak:Unstructured",
    "jcr:content":
    {
      "jcr:primaryType":"oak:Unstructured",
      "jcr:lastModified":
      {
        "jcr:primaryType":"oak:Unstructured",
        "type":"Date"
      }
    }
  }	
type
JCR Property type. Can be one of Date, Boolean, Double or Long
boost
The boost value. Defaults to 1.0
Since 1.0.9

Ordering

Lucene property index provides efficient sorting support based on Lucene DocValue fields. To configure specify the list of property names which can be used in the order by clause as part of orderedProps property.

If the property is of type other than string then you must specify the property definition with type details

Refer to Lucene based Sorting for more details.

LuceneIndexProvider Configuration

Some of the runtime aspects of the Oak Lucene support can be configured via OSGi configuration. The configuration needs to be done for PID org.apache .jackrabbit.oak.plugins.index.lucene.LuceneIndexProviderService

OSGi Configuration

enableCopyOnReadSupport
Enable copying of Lucene index to local file system to improve query performance. See Copy Indexes On Read
localIndexDir
Directory to be used for when copy index files to local file system. To be specified when enableCopyOnReadSupport is enabled
debug
Boolean value. Defaults to false
If enabled then Lucene logging would be integrated with Slf4j

Non Root Index Definitions

Lucene index definition can be defined at any location in repository and need not always be defined at root. For example if your query involves path restrictions like

select * from [app:Asset] as a where ISDESCENDANTNODE(a, '/content/companya') and [format] = 'image'

Then you can create the required index definition say assetIndex at /content/companya/oak:index/assetIndex. In such a case that index would contain data for the subtree under /content/companya

Native Query and Index Selection

Oak query engine supports native queries like

//*[rep:native('lucene', 'name:(Hello OR World)')]

If multiple Lucene based indexes are enabled on the system and you need to make use of specific Lucene index like /oak:index/assetIndex then you can specify the index name via functionName attribute on index definition.

For example for assetIndex definition like

{
  "jcr:primaryType":"oak:QueryIndexDefinition",
  "type":"lucene",
  ...
  "functionName" : "lucene-assetIndex",
}

Executing following query would ensure that Lucene index from assetIndex should be used

//*[rep:native('lucene-assetIndex', 'name:(Hello OR World)')]

Persisting indexes to FileSystem

By default Lucene indexes are stored in the NodeStore. If required they can be stored on the file system directly

{
  "jcr:primaryType":"oak:QueryIndexDefinition",
  "type":"lucene",
  ...
  "persistence" : "file",
  "path" : "/path/to/store/index"
}

To store the Lucene index in the file system, in the Lucene index definition node, set the property persistence to file, and set the property path to the directory where the index should be stored. Then start reindexing by setting reindex to true.

Note that this setup would only for those non cluster NodeStore. If the backend NodeStore supports clustering then index data would not be accessible on other cluster nodes

CopyOnRead

Lucene indexes are stored in NodeStore. Oak Lucene provides a custom directory implementation which enables Lucene to load index from NodeStore. This might cause performance degradation if the NodeStore storage is remote. For such case Oak Lucene provide a CopyOnReadDirectory which copies the index content to a local directory and enables Lucene to make use of local directory based indexes while performing queries.

At runtime various details related to copy on read features are exposed via CopyOnReadStats MBean. Indexes at JCR path e.g. /oak:index/assetIndex would be copied to <index dir>/<hash of jcr path>. To determine mapping between local index directory and JCR path refer to the MBean details

CopyOnReadStats

For more details refer to OAK-1724. This feature can be enabled via Lucene Index provider service configuration

Lucene Index MBeans

Oak Lucene registers a JMX bean LuceneIndex which provide details about the index content e.g. size of index, number of documents present in index etc

Lucene Index MBean

Analyzing created Lucene Index

Luke is a handy development and diagnostic tool, which accesses already existing Lucene indexes and allows you to display index details. In Oak Lucene index files are stored in NodeStore and hence not directly accessible. To enable analyzing the index files via Luke follow below mentioned steps

  1. Download the Luke version which includes the matching Lucene jars used by Oak. As of Oak 1.0.8 release the Lucene version used is 4.7.1. So download the jar from here

    $wget https://github.com/DmitryKey/luke/releases/download/4.7.0/luke-with-deps.jar
    
  2. Use the Oak Console to dump the Lucene index from NodeStore to filesystem directory. Use the lc dump command

    $ java -jar oak-run-*.jar console /path/to/oak/repository
    Apache Jackrabbit Oak 1.1-SNAPSHOT
    Jackrabbit Oak Shell (Apache Jackrabbit Oak 1.1-SNAPSHOT, JVM: 1.7.0_55)
    Type ':help' or ':h' for help.
    -------------------------------------------------------------------------
    /> lc info /oak:index/lucene
    Index size : 74.1 MB
    Number of documents : 235708
    Number of deleted documents : 231
    /> lc 
    dump   info   
    /> lc dump /path/to/dump/index/lucene /oak:index/lucene
    Copying Lucene indexes to [/path/to/dump/index/lucene]
    Copied 74.1 MB in 1.209 s
    /> lc dump /path/to/dump/index/slingAlias /oak:index/slingAlias
    Copying Lucene indexes to [/path/to/dump/index/lucene-index/slingAlias]
    Copied 8.5 MB in 218.7 ms
    />
    
  3. Post dump open the index via Luke. Oak Lucene uses a custom Codec. So oak-lucene jar needs to be included in Luke classpath for it to display the index details

    $ java -XX:MaxPermSize=512m luke-with-deps.jar:oak-lucene-1.0.8.jar org.getoptuke.Luke
    

From the Luke UI shown you can access various details.

Index performance

Following are some best practices to get good performance from Lucene based indexes

  1. Make use on non root indexes. If you query always perform search under certain paths then create index definition under those paths only. This might be helpful in multi tenant deployment where each tenant data is stored under specific repository path and all queries are made under those path.

  2. Index only required data. Depending on your requirement you can create multiple Lucene indexes. For example if in majority of cases you are querying on various properties specified under <node>/jcr:content/metadata where node belong to certain specific nodeType then create single index definition listing all such properties and restrict it that nodeType. You can the size of index via mbean