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Lucene Index

Oak supports Lucene based indexes to support both property constraint and full text constraints. Depending on the configuration a Lucene index can be used to evaluate property constraints, full text constraints, path restrictions and sorting.

SELECT * FROM [nt:base] WHERE [assetType] = 'image'

Following index definition would allow using Lucene index for above query

/oak:index/assetType
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - async = "async"
  + indexRules
    - jcr:primaryType = "nt:unstructured"
    + nt:base
      + properties
        - jcr:primaryType = "nt:unstructured"
        + assetType
          - propertyIndex = true
          - name = "assetType"

The index definition node for a lucene-based 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

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. To support following query

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

The Lucene index needs to be configured to index all properties

/oak:index/assetType
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - async = "async"
  + indexRules
    - jcr:primaryType = "nt:unstructured"
    + nt:base
      + properties
        - jcr:primaryType = "nt:unstructured"
        + allProps
          - name = ".*"
          - isRegexp = true
          - nodeScopeIndex = true

Index Definition

Lucene index definition consist of indexingRules, analyzers , aggregates etc which determine which node and properties are to be indexed and how they are indexed.

Below is the canonical index definition structure

luceneIndex (oak:QueryIndexDefinition)
  - type (string) = 'lucene' mandatory
  - async (string) = 'async' mandatory
  - blobSize (long) = 32768
  - maxFieldLength (long) = 10000
  - evaluatePathRestrictions (boolean) = false
  - name (string)
  - compatVersion (long) = 2
  - includedPaths (string) multiple
  - excludedPaths (string) multiple
  - queryPaths (string) multiple = ['/']
  - indexPath (string)
  - codec (string)
  + indexRules (nt:unstructured)
  + aggregates (nt:unstructured)
  + analyzers (nt:unstructured)
  + tika (nt:unstructured)

Following are the config options which can be defined at the index definition level

type
Required and should always be lucene
async
Required and should always be async
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
evaluatePathRestrictions
Optional boolean property defaults to false
If enabled the index can evaluate path restrictions
includedPaths
Optional multi value property. Defaults to ‘/’
List of paths which should be included in indexing.
excludedPaths
Optional multi value property. Defaults to empty
List of paths which should be excluded from indexing.
queryPaths
Optional multi value property. Defaults to ‘/’
List of paths for which the index can be used to perform queries. Refer to Path Includes/Excludes for more details
indexPath
Optional string property to specify index path
Path of the index definition in the repository. For e.g. if the index definition is specified at /oak:index/lucene then set this path in indexPath
codec
Optional string property
Name of the Lucene codec to use
name
Optional property
Captures the name of the index which is used while logging
compatVersion
Required integer property and should be set to 2
By default Oak uses older Lucene index implementation which does not supports property restrictions, index time aggregation etc. To make use of this feature set it to 2. Please note for full text indexing with compatVersion 2, at query time, only the access right of the parent (aggregate) node is checked, and the access right of the child nodes is not checked. If this is a security concern, then compatVersion should not be set, so that query time aggregation is used, in which case the access right of the relevant child is also checked. A compatVersion 2 full text index is usually faster to run queries.
maxFieldLength
Numbers of terms indexed per field. Defaults to 10000

Indexing Rules

Indexing rules defines which types of node and properties are indexed. An index configuration can define one or more indexingRules for different nodeTypes.

fulltextIndex
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - async = "async"
  + indexRules
    - jcr:primaryType = "nt:unstructured"
    + app:Page
      + properties
        - jcr:primaryType = "nt:unstructured"
        + publishedDate
          - propertyIndex = true
          - name = "jcr:content/publishedDate"
    + app:Asset
      + properties
        - jcr:primaryType = "nt:unstructured"
        + imageType
          - propertyIndex = true
          - name = "jcr:content/metadata/imageType"

Rules are defined per nodeType and each rule has one or more property definitions determine which properties are indexed. Below is the canonical index definition structure

ruleName (nt:unstructured)
  - inherited (boolean) = true
  - indexNodeName (boolean) = false
  - includePropertyTypes (string) multiple
  + properties (nt:unstructured)

Following are the config options which can be defined at the index rule level

inherited
Optional boolean property defaults to true
Determines if the rule is applicable on exact match or can be applied if match is done on basis of nodeType inheritance
includePropertyTypes
Applicable when index is enabled for fulltext indexing
For full text index defaults to include all types
String array of property types which should be indexed. The values can be one specified in PropertyType Names

indexNodeName
@since Oak 1.0.20, 1.2.5
Default to false. If set to true then index would also be created for node name. This would enable faster evaluation of queries involving constraints on Node name. For example
  • select [jcr:path] from [nt:base] where NAME() = ‘kite’
  • select [jcr:path] from [nt:base] where NAME() LIKE ‘kite%’
  • //kite
  • //*[jcr:like(fn:name(), ‘kite%’)]
  • //element(*, app:Asset)[fn:name() = ‘kite’]
  • //element(kite, app:Asset)
Cost Overrides

By default, the cost of using this index is calculated follows: For each query, the overhead is one operation. For each entry in the index, the cost is one. The following only applies to compatVersion 2 only: To use use a lower or higher cost, you can set the following optional properties in the index definition:

- costPerExecution (Double) = 1.0
- costPerEntry (Double) = 1.0

Please note that typically, those settings don’t need to be explicitly set. Cost per execution is the overhead of one query. Cost per entry is the cost per node in the index. Using 0.5 means the cost is half, which means the index would be used used more often (that is, even if there is a different index with similar cost).

Indexing Rule inheritance

indexRules are defined per nodeType and support nodeType inheritance. For example while indexing any node the indexer would lookup for applicable indexRule for that node based on its primaryType. If a direct match is found then that rule would be used otherwise it would look for rule for any of the parent types. The rules are looked up in the order of there entry under indexRules node (indexRule node itself is of type nt:unstructured which has orderable child nodes)

If inherited is set to false on any rule then that rule would only be applicable if exact match is found

Property Definitions

Each index rule consist of one ore more property definition defined under properties. Order of property definition node is important as some properties are based on regular expressions. Below is the canonical property definition structure

propNode (nt:unstructured)
  - name (string)
  - boost (double) = '1.0'
  - index (boolean) = true
  - useInExcerpt (boolean) = false
  - analyzed (boolean) = false
  - nodeScopeIndex (boolean) = false
  - ordered (boolean) = false
  - isRegexp (boolean) = false
  - type (string) = 'undefined'
  - propertyIndex (boolean) = false
  - nullCheckEnabled (boolean) = false
  - excludeFromAggregation (boolean) = false

Following are the details about the above mentioned config options which can be defined at the property definition level

name
Property name. If not defined then property name is set to the node name. If isRegexp is true then it defines the regular expression. Can also be set to a relative property.
isRegexp
If set to true then property name would be interpreted as a regular expression and the given definition would be applicable for matching property names. Note that expression should be structured such that it does not match ‘/’.
  • .* - This property definition is applicable for all properties of given node
  • jcr:content/metadata/.* - This property definition is applicable for all properties of child node jcr:content/metadata
boost
If the property is included in nodeScopeIndex then it defines the boost done for the index value against the given property name. See Boost and Search Relevancy for more details
index
Determines if this property should be indexed. Mostly useful for fulltext index where some properties need to be excluded from getting indexed.
useInExcerpt
Controls whether the value of a property should be used to create an excerpt. The value of the property is still full-text indexed when set to false, but it will never show up in an excerpt for its parent node. If set to true then property value would be stored separately within index causing the index size to increase. So set it to true only if you make use of excerpt feature
nodeScopeIndex
Control whether the value of a property should be part of fulltext index. That is, you can do a jcr:contains(., ‘foo’) and it will return nodes that have a string property that contains the word foo. Example
  • //element(*, app:Asset)[jcr:contains(., ‘image’)]

In case of aggregation all properties would be indexed at node level by default if the property type is part of includePropertyTypes. However if there is an explicit property definition provided then it would only be included if nodeScopeIndex is set to true.

analyzed
Set this to true if the property is used as part of contains. Example
  • //element(*, app:Asset)[jcr:contains(type, ‘image’)]
  • //element(*, app:Asset)[jcr:contains(jcr:content/metadata/@format, ‘image’)]
ordered
If the property is to be used in order by clause to perform sorting then this should be set to true. This should be set to true only if the property is to be used to perform sorting as it increases the index size. Example
  • //element(*, app:Asset)[jcr:contains(type, ‘image’)] order by @size
  • //element(*, app:Asset)[jcr:contains(type, ‘image’)] order by jcr:content/@jcr:lastModified

Refer to Lucene based Sorting for more details. Note that this is only supported for single value property. Enabling this on multi value property would cause indexing to fail.

type
JCR Property type. Can be one of Date, Boolean, Double , String or Long. Mostly inferred from the indexed value. However in some cases where same property type is not used consistently across various nodes then it would recommended to specify the type explicitly.
propertyIndex
Whether the index for this property is used for equality conditions, ordering, and is not null conditions.
nullCheckEnabled
Since 1.0.12
If the property is checked for is null then this should be set to true. This should only be enabled for nodeTypes which are not generic as it leads to index entry for all nodes of that type where this property is not set.
  • _//element(*, app:Asset)[not(jcr:content/@excludeFromSearch)]

It would be better to use a query which checks for property existence or property being set to specific values as such queries can make use of index without any extra storage cost.

Refer to IS NULL support for more details

excludeFromAggregation
Since 1.0.27, 1.2.11
if set to true the property would be excluded from aggregation OAK-3981

Property Names

Property name can be one of following

  1. Simple name - Like assetType etc. These are used for properties which are defined directly on the indexed node
  2. Relative name - Like jcr:content/metadata/title. These are used for properties which are defined relative to the node being indexed.
  3. Regular Expression - Like .*. Used when only property whose name match given pattern are to be indexed. They can also be used for relative properties like jcr:content/metadata/dc:.*$ which indexes all property names starting with dc from node with relative path jcr:content/metadata
  4. The string :nodeName - this special case indexes node name as if it’s a virtual property of the node being indexed. Setting this along with nodeScopeIndex=true is akin to setting indexNodeName=true on indexing rule. (@since Oak 1.3.15, 1.2.14)

Evaluate Path Restrictions

Lucene index provides support for evaluating path restrictions natively. Consider a query like

select * from [app:Asset] as a where isdescendantnode(a, [/content/app/old]) AND contains(*, 'white')

By default the index would return all node which contain white and Query engine would filter out nodes which are not under /content/app/old. This can perform slow if lots of nodes are not under that path. To speed up such queries one can enable evaluatePathRestrictions in Lucene index and index would only return nodes which are under /content/app/old.

Enabling this feature would incur cost in terms of slight increase in index size. Refer to OAK-2306 for more details.

Include and Exclude paths from indexing

@since Oak 1.0.14, 1.2.3

By default the indexer would index all the nodes under the subtree where the index definition is defined as per the indexingRule. In some cases its required to index nodes under certain path. For e.g. if index is defined for global fulltext index which include the complete repository you might want to exclude certain path which contains transient system data.

For example if you application stores certain logs under /var/log and it is not supposed to be indexed as part of fulltext index then it can be excluded

/oak:index/assetType
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - excludedPaths = ["/var/log"]

Above index definition would cause nodes under /var/log not to be indexed. In majority of case excludedPaths only makes sense. However in some cases it might be required to also specify explicit set of path which should be indexed. In that case make use of includedPaths

Note that excludedPaths and includedPaths does not affect the index selection logic for a query i.e. if a query has any path restriction specified then that would not be checked against the excludedPaths and includedPaths.

queryPaths

If you need to ensure that a given index only gets used for query with specific path restrictions then you need to specify those paths in queryPaths.

For example if includedPaths and queryPaths are set to [ “/content/a”, “/content/b” ]. The index would be used for queries below “/content/a” as well as for queries below “/content/b”. But not for queries without path restriction, or for queries below “/content/c”.

Usage

Key points to consider while using excludedPaths, includedPaths and queryPaths

  1. Reduce what gets indexed in global fulltext index - For setups where a global fulltext index is configured say at /oak:index/lucene which indexes everything then excludedPaths can be used to avoid indexing transient repository state like in ‘/var’ or ‘/tmp’. This would help in improving indexing rate. By far this is the primary usecase

  2. Reduce reindexing time - If its known that certain type of data is stored under specific subtree only but the query is not specifying that path restriction then includedPaths can be used to reduce reindexing time for existing content by ensuring that indexing logic only traverses that path for building up the index

  3. Use excludedPaths, includedPaths with caution - When paths are excluded or included then query engine is not aware of that. If wrong paths get excluded then its possible that nodes which should have been part of query result get excluded as they are not indexed. So only exclude those paths which do not have node matching given nodeType or nodes which are known to be not part of any query result

  4. Sub-root index definitions (e.g. /test/oak:index/index-def-node) - excludedPaths and includedPaths need to be relative to the path that index is defined for. e.g. if the condition is supposed to be put for /test/a where the index definition is at /test/oak:index/index-def-node then /a needs to be put as value of excludedPaths or includedPaths. On the other hand, queryPaths remains to be an absolute path. So, for the example above, queryPaths would get the value /test/a.

In most cases use of queryPaths would not be required as index definition should not have any overlap.

Refer to OAK-2599 for more details.

Aggregation

Sometimes it is useful to include the contents of descendant nodes into a single node to easier search on content that is scattered across multiple nodes.

Oak allows you to define index aggregates based on relative path patterns and primary node types. Changes to aggregated items cause the main item to be reindexed, even if it was not modified.

Aggregation configuration is defined under the aggregates node under index configuration. The following example creates an index aggregate on nt:file that includes the content of the jcr:content node:

fulltextIndex
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - async = "async"
  + aggregates
    + nt:file
      + include0
        - path = "jcr:content"

By default all properties whose type matches includePropertyTypes and are part of child nodes as per the aggregation pattern are included for indexing. For excluding certain properties define a property definition with relative path and set excludeFromAggregation to true. Such properties would then be excluded from fulltext index

For a given nodeType multiple includes can be defined. Below is the aggregate definition structure for any specific include rule

aggregateNodeInclude (nt:unstructured)
  - path (string) mandatory
  - primaryType (string)
  - relativeNode (boolean) = false

Following are the details about the above mentioned config options which can be defined as part of aggregation include. (Refer to OAK-2268 for implementation details)

path
Path pattern to include. Example
  • jcr:content - Name explicitly specified
  • * - Any child node at depth 1
  • */* - Any child node at depth 2
primaryType

Restrict the included nodes to a certain type. The restriction would be applied on the last node in given path

+ aggregates
  + nt:file
    + include0
      - path = "jcr:content"
      - primaryType = "nt:resource"
relativeNode

Boolean property indicates that query can be performed against specific node For example for following content

+ space.txt (app:Asset)
  + renditions (nt:folder)
    + original (nt:file)
      + jcr:content (nt:resource)
        - jcr:data

And a query like

    select * from [app:Asset] where contains(renditions/original/*, "pluto")

Following index configuration would be required

    fulltextIndex
      - jcr:primaryType = "oak:QueryIndexDefinition"
      - compatVersion = 2
      - type = "lucene"
      - async = "async"
      + aggregates
        + nt:file
          + include0
            - path = "jcr:content"
        + app:Asset
          + include0
            - path = "renditions/original"
            - relativeNode = true
      + indexRules
        - jcr:primaryType = "nt:unstructured"
        + app:Asset

Aggregation and Recursion

While performing aggregation the aggregation rules are again applied on node being aggregated. For example while aggregating for app:Asset above when renditions/original/* is being aggregated then aggregation rule would again be applied. In this case as renditions/original is nt:file then aggregation rule applicable for nt:file would be applied. Such a logic might result in recursion. (See JCR-2989 for details).

For such case reaggregateLimit is set on aggregate definition node and defaults to 5

  + aggregates
    + app:Asset
      - reaggregateLimit (long) = 5
      + include0
        - path = "renditions/original"
        - relativeNode = true

Analyzers

@since Oak 1.5.5, 1.4.7 Unless custom analyzer is configured (as documented below), in-built analyzer can be configured to include original term as well to be indexed. This is controlled by setting boolean property indexOriginalTerm on analyzers node.

/oak:index/assetType
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  + analyzers
    - indexOriginalTerm = true

(See OAK-4516 for details)

@since Oak 1.2.0

Analyzers can be configured as part of index definition via analyzers node. The default analyzer can be configured via analyzers/default node

+ sampleIndex
    - jcr:primaryType = "oak:QueryIndexDefinition"
    + analyzers
        + default
        + pathText
        ...
Specify analyzer class directly

If any of the out of the box analyzer is to be used then it can configured directly

+ analyzers
        + default
            - class = "org.apache.lucene.analysis.standard.StandardAnalyzer"
            - luceneMatchVersion = "LUCENE_47" (optional)

To confirm to specific version specify it via luceneMatchVersion otherwise Oak would use a default version depending on version of Lucene it is shipped with.

One can also provide a stopword file via stopwords nt:file node under the analyzer node

+ analyzers
        + default
            - class = "org.apache.lucene.analysis.standard.StandardAnalyzer"
            - luceneMatchVersion = "LUCENE_47" (optional)
            + stopwords (nt:file)
Create analyzer via composition

Analyzers can also be composed based on Tokenizers, TokenFilters and CharFilters. This is similar to the support provided in Solr where you can configure analyzers in xml

+ analyzers
        + default
            + charFilters (nt:unstructured) //The filters needs to be ordered
                + HTMLStrip
                + Mapping
            + tokenizer
                - name = "Standard"
            + filters (nt:unstructured) //The filters needs to be ordered
                + LowerCase
                + Stop
                    - words = "stop1.txt, stop2.txt"
                    + stop1.txt (nt:file)
                    + stop2.txt (nt:file)
                + PorterStem
                + Synonym
                    - synonyms = "synonym.txt"
                    + synonym.txt (nt:file)

Points to note

  1. Name of filters, charFilters and tokenizer are formed by removing the factory suffixes. So
    • org.apache.lucene.analysis.standard.StandardTokenizerFactory -> Standard
    • org.apache.lucene.analysis.charfilter.MappingCharFilterFactory -> Mapping
    • org.apache.lucene.analysis.core.StopFilterFactory -> Stop
  2. Any config parameter required for the factory is specified as property of that node
    • If the factory requires to load a file e.g. stop words from some file then file content can be provided via creating child nt:file node of the filename
  3. The analyzer-chain processes text from nodes as well text passed in query. So, do take care that any mapping configuration (e.g. synonym mappings) factor in the chain of analyzers. E.g a common mistake for synonym mapping would be to have domain => Range while there’s a lower case filter configured as well (see the example above). For such a setup an indexed value domain would actually get indexed as Range (mapped value doesn’t have lower case filter below it) but a query for Range would actually query for range (due to lower case filter) and won’t give the result (as might be expected). An easy work-around for this example could be to have lower case mappings i.e. just use domain => range.
  4. Precedence: Specifying analyzer class directly has precedence over analyzer configuration by composition. If you want to configure analyzers by composition then analyzer class MUST NOT not be specified. In-build analyzer has least precedence and comes into play only if no custom analyzer has been configured. Similary, setting indexOriginalTerm on analyzers node to modify behavior of in-built analyzer also works only when no custom analyzer has been configured.

Codec

Name of Lucene Codec to use. By default if the index involves fulltext indexing then Oak Lucene uses OakCodec which disables compression. Due to this the index size may grow large. To enable compression you can set the codec to Lucene46

/oak:index/assetType
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - codec = "Lucene46"

Refer to OAK-2853 for details. Enabling the Lucene46 codec would lead to smaller and compact indexes.

Boost and Search Relevancy

@since Oak 1.2.5

When fulltext indexing is enabled then internally Oak would create a fulltext field which consists of text extracted from various other fields i.e. fields for which nodeScopeIndex is true. This allows search like //*[jcr:contains(., 'foo')] to perform search across any indexable field containing foo (See contains function for details)

In certain cases its desirable that those nodes where the searched term is present in a specific property are ranked higher (come earlier in search result) compared to those node where the searched term is found in some other property.

In such cases it should be possible to boost specific text contributed by individual property. Meaning that if a title field is boosted more than description, then search result would those node coming earlier where searched term is found in title field

For that to work ensure that for each such property (which need to be preferred) both nodeScopeIndex and analyzed are set to true. In addition you can specify boost property so give higher weightage to values found in specific property

Note that even without setting explicit boost and just setting nodeScopeIndex and analyzed to true would improve the search result due to the way Lucene does scoring. Internally Oak would create separate Lucene fields for those jcr properties and would perform a search across all such fields. For more details refer to OAK-3367

  + indexRules
    - jcr:primaryType = "nt:unstructured"
    + app:Asset
      + properties
        - jcr:primaryType = "nt:unstructured"
        + description
          - nodeScopeIndex = true
          - analyzed = true
          - name = "jcr:content/metadata/jcr:description"
        + title
          - analyzed = true
          - nodeScopeIndex = true
          - name = "jcr:content/metadata/jcr:title"
          - boost = 2.0

With above index config a search like

SELECT
  *
FROM [app:Asset] 
WHERE 
  CONTAINS(., 'Batman')

Would have those node (of type app:Asset) come first where Batman is found in jcr:title. While those nodes where search text is found in other field like aggregated content would come later

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
enableCopyOnWriteSupport
Enable copying of Lucene index to local file system to improve indexing performance. See Copy Indexes On Write
localIndexDir
Directory to be used for when copy index files to local file system. To be specified when enableCopyOnReadSupport is enabled
prefetchIndexFiles
Prefetch the index files when CopyOnRead is enabled. When enabled all new Lucene index files would be copied locally before the index is made available to QueryEngine (1.0.17,1.2.3)
debug
Boolean value. Defaults to false
If enabled then Lucene logging would be integrated with Slf4j

Tika Config

@since Oak 1.0.12, 1.2.3

Oak Lucene uses Apache Tika to extract the text from binary content

+ tika
    - maxExtractLength (long) = -10
    + config.xml  (nt:file)
      + jcr:content
        - jcr:data = //config xml binary content

Oak uses a default config. To use a custom config specify the config file via tika/config.xml node in index config.

maxExtractLength
Limits the number of characters that are extracted by the Tika parse. A negative value indicates a multiple of maxFieldLength and a positive value is used as is
  • maxExtractLength = -10, maxFieldLength = 10000 -> Actual value = 100000
  • maxExtractLength = 1000 -> Actual value = 1000

Mime type usage

A binary would only be index if there is an associated property jcr:mimeType defined and that is supported by Tika. By default indexer uses TypeDetector instead of default DefaultDetector which relies on the jcr:mimeType to pick up the right parser.

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

With Oak 1.0.13 this feature is now enabled by default.

CopyOnWrite

@since Oak 1.0.15, 1.2.3

Similar to CopyOnRead feature Oak Lucene also supports CopyOnWrite to enable faster indexing by first buffering the writes to local filesystem and transferring them to remote storage asynchronously as the indexing proceeds. This should provide better performance and hence faster indexing times.

indexPath

To speed up the indexing with CopyOnWrite you would also need to set indexPath in index definition to the path of index in the repository. For e.g. if your index is defined at /oak:index/lucene then value of indexPath should be set to /oak:index/lucene. This would enable the indexer to perform any read during the indexing process locally and thus avoid costly read from remote

For more details refer to OAK-2247. 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 -cp luke-with-deps.jar:oak-lucene-1.0.8.jar org.getopt.luke.Luke
    

From the Luke UI shown you can access various details.

Pre-Extracting Text from Binaries

@since Oak 1.0.18, 1.2.3

Lucene indexing is performed in a single threaded mode. Extracting text from binaries is an expensive operation and slows down the indexing rate considerably. For incremental indexing this mostly works fine but if performing a reindex or creating the index for the first time after migration then it increases the indexing time considerably.

To speed up the Lucene indexing for such cases i.e. reindexing, we can decouple the text extraction from actual indexing.

  1. Extract and store the extracted text from binaries via oak-run tool
  2. Configure a PreExtractedTextProvider which can lookup extracted text and thus avoid text extraction at time of actual indexing

Below are details around steps required for making using of this feature

  1. Generate the csv file containing binary file details

    java -cp tika-app-1.8.jar:oak-run.jar \
    org.apache.jackrabbit.oak.run.Main tika \  
    --fds-path /path/to/datastore \
    --nodestore /path/to/segmentstore --data-file dump.csv generate
    
  2. Extract the text

    java -cp tika-app-1.8.jar:oak-run.jar \
    org.apache.jackrabbit.oak.run.Main tika \
    --data-file binary-stats.csv \
    --store-path ./store 
    --fds-path /path/to/datastore  extract
    
  3. Configure the PreExtractedTextProvider - Once the extraction is performed configure a PreExtractedTextProvider within the application such that Lucene indexer can make use of that to lookup extracted text.

    For this look for OSGi config for Apache Jackrabbit Oak DataStore PreExtractedTextProvider

    OSGi Configuration

Once PreExtractedTextProvider is configured then upon reindexing Lucene indexer would make use of it to check if text needs to be extracted or not. Check TextExtractionStatsMBean for various statistics around text extraction and also to validate if PreExtractedTextProvider is being used.

For more details on this feature refer to OAK-2892

Advanced search features

Suggestions

@since Oak 1.1.17, 1.0.15

In order to use Lucene index to perform search suggestions, the index definition node (the one of type oak:QueryIndexDefinition) needs to have the compatVersion set to 2, then one or more property nodes, depending on use case, need to have the property useInSuggest set to true, such setting controls from which properties terms to be used for suggestions will be taken.

Once the above configuration has been done, by default, the Lucene suggester is updated every 10 minutes but that can be changed by setting the property suggestUpdateFrequencyMinutes in suggestion node under the index definition node to a different value. Note that up till Oak 1.3.14/1.2.14, suggestUpdateFrequencyMinutes was to be setup at index definition node itself. That is is still supported for backward compatibility, but having a separate suggestion node is preferred.

Sample configuration for suggestions based on terms contained in jcr:description property.

/oak:index/lucene-suggest
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - async = "async"
  + suggestion
    - suggestUpdateFrequencyMinutes = 20
  + indexRules
    - jcr:primaryType = "nt:unstructured"
    + nt:base
      + properties
        - jcr:primaryType = "nt:unstructured"
        + jcr:description
          - propertyIndex = true
          - analyzed = true
          - useInSuggest = true

@since Oak 1.3.12, 1.2.14 the index Analyzer can be used to perform a have more fine grained suggestions, e.g. single words (whereas default suggest configuration returns entire property values, see [OAK-3407]: https://issues.apache.org/jira/browse/OAK-3407). Analyzed suggestions can be enabled by setting “suggestAnalyzed” property to true, e.g.:

/oak:index/lucene-suggest
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - async = "async"
  + suggestion
    - suggestUpdateFrequencyMinutes = 20
    - suggestAnalyzed = true

Note that up till Oak 1.3.14/1.2.14, suggestAnalyzed was to be setup at index definition node itself. That is is still supported for backward compatibility, but having a separate suggestion node is preferred.

Setting up useInSuggest=true for a property definition having name=:nodeName would add node names to suggestion dictionary (See property name for node name indexing)

Since, Oak 1.3.16/1.2.14, very little support exists for queries with ISDESCENDANTNODE constraint to subset suggestions on a sub-tree. It requires evaluatePathRestrictions=true on index definition. e.g. SELECT rep:suggest() FROM [nt:base] WHERE SUGGEST('test') AND ISDESCENDANTNODE('/a/b') or /jcr:root/a/b//[rep:suggest('in 201')]/(rep:suggest()) Note, the subset is done by filtering top 10 suggestions. So, it’s possible to get no suggestions for a subtree query, if top 10 suggestions are not part of that subtree. For details look at OAK-3994 and related issues.

Spellchecking

@since Oak 1.1.17, 1.0.13

In order to use Lucene index to perform spellchecking, the index definition node (the one of type oak:QueryIndexDefinition) needs to have the compatVersion set to 2, then one or more property nodes, depending on use case, need to have the property useInSpellcheck set to true, such setting controls from which properties terms to be used for spellcheck corrections will be taken.

Sample configuration for spellchecking based on terms contained in jcr:title property.

Since Oak 1.3.11/1.2.14, the each suggestion would be returned per row.

/oak:index/lucene-spellcheck
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - async = "async"
  + indexRules
    - jcr:primaryType = "nt:unstructured"
    + nt:base
      + properties
        - jcr:primaryType = "nt:unstructured"
        + jcr:title
          - propertyIndex = true
          - analyzed = true
          - useInSpellcheck = true

Since, Oak 1.3.16/1.2.14, very little support exists for queries with ISDESCENDANTNODE constraint to subset suggestions on a sub-tree. It requires evaluatePathRestrictions=true on index definition. e.g. SELECT rep:suggest() FROM [nt:base] WHERE SUGGEST('test') AND ISDESCENDANTNODE('/a/b') or /jcr:root/a/b//[rep:suggest('in 201')]/(rep:suggest()) Note, the subset is done by filtering top 10 spellchecks. So, it’s possible to get no results for a subtree query, if top 10 spellchecks are not part of that subtree. For details look at OAK-3994 and related issues.

Facets

@since Oak 1.3.14

Lucene property indexes can also be used for retrieving facets, in order to do so the property facets must be set to true on the property definition.

/oak:index/lucene-with-facets
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - async = "async"
  + indexRules
    - jcr:primaryType = "nt:unstructured"
    + nt:base
      + properties
        - jcr:primaryType = "nt:unstructured"
        + jcr:title
          - facets = true
          - propertyIndex = true

Specific facet related features for Lucene property index can be configured in a separate facets node below the index definition. By default ACL checks are always performed on facets by the Lucene property index however this can be avoided by setting the property secure to false in the facets configuration node. + nt:base + properties - jcr:primaryType = "nt:unstructured" + jcr:title - facets = true - propertyIndex = true + facets - secure = false

Score Explanation

@since Oak 1.3.12

Lucene supports explanation of scores which can be selected in a query using a virtual column oak:scoreExplanation. e.g. select [oak:scoreExplanation], * from [nt:base] where foo='bar'

Note that showing explanation score is expensive. So, this feature should be used for debug purposes only.

Custom hooks

@since Oak 1.3.14

In OSGi enviroment, implementations of IndexFieldProvider and FulltextQueryTermsProvider under org.apache.jackrabbit.oak.plugins.index.lucene.spi (see javadoc here) are called during indexing and querying as documented in javadocs.

Design Considerations

Lucene index provides quite a few features to meet various query requirements. While defining the index definition do consider the following aspects

  1. If query uses different path restrictions keeping other restrictions same then make use of evaluatePathRestrictions

  2. If query performs sorting then have an explicit property definition for the property on which sorting is being performed and set ordered to true for that property

  3. If the query is based on specific nodeType then define indexRules for that nodeType

  4. Aim for a precise index configuration which indexes just the right amount of content based on your query requirement. An index which is precise would be smaller and would perform better.

  5. Make use of nodetype to achieve a cohesive index. This would allow multiple queries to make use of same index and also evaluation of multiple property restrictions natively in Lucene

  6. Non root indexes - If your 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.

    In fact its recommended to use single index if all the properties being indexed are related. This would enable Lucene index to evaluate as much property restriction as possible natively (which is faster) and also save on storage cost incurred in storing the node path.

  7. Use features when required - There are certain features provided by Lucene index which incur extra cost in terms of storage space when enabled. For example enabling evaluatePathRestrictions, ordering etc. Enable such option only when you make use of those features and further enable them for only those properties. So ordering should be enabled only when sorting is being performed for those properties and evaluatePathRestrictions should only be enabled if you are going to specify path restrictions.

  8. Avoid overlapping index definition - Do not have overlapping index definition indexing same nodetype but having different includedPaths and excludedPaths. Index selection logic does not make use of the includedPaths and excludedPaths for index selection. Index selection is done only on cost basis and queryPaths. Having multiple definition for same type would cause ambiguity in index selection and may lead to unexpected results. Instead have a single index definition for same type.

Following analogy might be helpful to people coming from RDBMS world. Treat your nodetype as Table in your DB and all the direct or relative properties as columns in that table. Various property definitions can then be considered as index for those columns.

Lucene Index vs Property Index

Lucene based index can be restricted to index only specific properties and in that case it is similar to Property Index. However it differs from property index in following aspects

  1. Lucene index is Asynchronous - Lucene indexing is done asynchronously with a default interval of 5 secs. If there are lots of writes and those writes are related to what is being indexed then it might cause further delay. Compared to this the property index are always synchronous and upto date.

    So if in your usecase you need the latest result then prefer Property Indexes over Lucene Index

  2. Lucene index cannot enforce uniqueness constraint - By virtue of it being asynchronous it cannot enforce uniqueness constraint.

Examples

A - Simple queries

In many cases the query is purely based on some specific property and is not restricted to any specific nodeType

SELECT
  *
FROM [nt:base] AS s
WHERE ISDESCENDANTNODE([/content/public/platform])
AND s.code = 'DRAFT'

Following index definition would allow using Lucene index for above query

/oak:index/assetType
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - async = "async"
  - evaluatePathRestrictions = true
  + indexRules
    - jcr:primaryType = "nt:unstructured"
    + nt:base
      + properties
        - jcr:primaryType = "nt:unstructured"
        + code
          - propertyIndex = true
          - name = "code"

Above definition

  • Indexes code property present on any node
  • Supports evaluation of path restriction i.e. ISDESCENDANTNODE([/content/public/platform]) via evaluatePathRestrictions
  • Has a single indexRule for nt:base as queries do not specify any explicit nodeType restriction

Now you have another query like SELECT * FROM [nt:base] AS s WHERE s.status = 'DONE'

Here we can either add another property to the above definition or create a new index definition altogether. By default prefer to club such indexes together

/oak:index/assetType
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - async = "async"
  - evaluatePathRestrictions = true
  + indexRules
    - jcr:primaryType = "nt:unstructured"
    + nt:base
      + properties
        - jcr:primaryType = "nt:unstructured"
        + code
          - propertyIndex = true
          - name = "code"
        + status
          - propertyIndex = true
          - name = "status"

Taking another example. Lets say you perform a range query like

SELECT
  [jcr:path],
  [jcr:score],
  *
FROM [nt:base] AS a
WHERE isdescendantnode(a, '/content')
AND [offTime] > CAST('2015-04-06T02:28:33.032-05:00' AS date)

This can also be clubbed in same index definition above

/oak:index/assetType
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - async = "async"
  - evaluatePathRestrictions = true
  + indexRules
    - jcr:primaryType = "nt:unstructured"
    + nt:base
      + properties
        - jcr:primaryType = "nt:unstructured"
        + code
          - propertyIndex = true
          - name = "code"
        + status
          - propertyIndex = true
          - name = "status"
        + offTime
          - propertyIndex = true
          - name = "offTime"

B - Queries for structured content

Queries in previous examples were based on mostly unstructured content where no nodeType restrictions were applied. However in many cases the nodes being queried confirm to certain structure. For example you have following content

/content/dam/assets/december/banner.png
  - jcr:primaryType = "app:Asset"
  + jcr:content
    - jcr:primaryType = "app:AssetContent"
    + metadata
      - dc:format = "image/png"
      - status = "published"
      - jcr:lastModified = "2009-10-9T21:52:31"
      - app:tags = ["properties:orientation/landscape", "marketing:interest/product"]
      - size = 450
      - comment = "Image for december launch"
      - jcr:title = "December Banner"
      + xmpMM:History
        + 1
          - softwareAgent = "Adobe Photoshop"
          - author = "David"
    + renditions (nt:folder)
      + original (nt:file)
        + jcr:content
          - jcr:data = ...

Content like above is then queried in multiple ways. So lets take first query

UC1 - Find all assets which are having status as published

SELECT
  *
FROM [app:Asset] AS a
WHERE 
  a.[jcr:content/metadata/status] = 'published'

For this following index definition would be have to be created

/oak:index/assetType
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - async = "async"
  + indexRules
    - jcr:primaryType = "nt:unstructured"
    + app:Asset
      + properties
        - jcr:primaryType = "nt:unstructured"
        + status
          - propertyIndex = true
          - name = "jcr:content/metadata/status"

Above index definition

  • Indexes all nodes of type app:Asset only
  • Indexes relative property jcr:content/metadata/status for all such nodes

UC2 - Find all assets which are having status as published sorted by last modified date

SELECT
  *
FROM [app:Asset] AS a
WHERE 
  a.[jcr:content/metadata/status] = 'published'
ORDER BY
  a.[jcr:content/metadata/jcr:lastModified] DESC

To enable above query the index definition needs to be updated to following

    + app:Asset
      + properties
        - jcr:primaryType = "nt:unstructured"
        + status
          - propertyIndex = true
          - name = "jcr:content/metadata/status"        
        + lastModified
          - propertyIndex = true
          - name = "jcr:content/metadata/jcr:lastModified"
          - ordered = true
          - type = Date

Above index definition

  • jcr:content/metadata/jcr:lastModified is marked as ordered enabling support order by evaluation i.e. sorting for such properties
  • Property type is set to Date
  • Indexes both status and jcr:lastModified

UC3 - Find all assets where comment contains december

SELECT
  *
FROM [app:Asset] 
WHERE 
  CONTAINS([jcr:content/metadata/comment], 'december')

To enable above query the index definition needs to be updated to following

    + app:Asset
      + properties
        - jcr:primaryType = "nt:unstructured"
        + comment
          - name = "jcr:content/metadata/comment"
          - analyzed = true

Above index definition

  • jcr:content/metadata/comment is marked as analyzed enabling evaluation of contains i.e. fulltext search
  • propertyIndex is not enabled as this property is not going to be used to perform equality check

UC4 - Find all assets which are created by David and refer to december

SELECT
  *
FROM [app:Asset] 
WHERE 
  CONTAINS(., 'december david')

Here we want to create a fulltext index for all assets. It would index all the properties in app:Asset including all relative nodes. To enable that we need to make use of aggregation

/oak:index/assetType
  - jcr:primaryType = "oak:QueryIndexDefinition"
  - compatVersion = 2
  - type = "lucene"
  - async = "async"
  + aggregates
    + app:Asset
      + include0
        - path = "jcr:content"
      + include1
        - path = "jcr:content/metadata"      
      + include2
        - path = "jcr:content/metadata/*"
      + include3
        - path = "jcr:content/metadata/*/*"        
      + include4
        - path = "jcr:content/renditions"
      + include5
        - path = "jcr:content/renditions/original" 
    + nt:file
      + include0
        - path = "jcr:content"
  + indexRules
    - jcr:primaryType = "nt:unstructured"
    + app:Asset
      - includePropertyTypes = ["String", "Binary"]
      + properties
        - jcr:primaryType = "nt:unstructured"
        + comment
          - propertyIndex = true
          - nodeScopeIndex = true
          - name = "jcr:content/metadata/comment"

Above index definition

  • Only indexes String and Binary properties as part of fulltext index via includePropertyTypes

  • Has aggregates defined for various relative paths like jcr:content, jcr:content/metadata, jcr:content/renditions/original etc.

    With these rules properties like banner.png/metadata/comment, banner.png/metadata/xmpMM:History/1/author get indexed as part for fulltext index for banner.png node.

  • Inclusion of jcr:content/renditions/original would lead to aggregation of jcr:content/renditions/original/jcr:content/jcr:data property also as aggregation logic would apply rules for nt:file while aggregating the original node

  • Aggregation would include by default all properties which are part of includePropertyTypes. However if any property has a explicit property definition provided like comment then nodeScopeIndex would need to be set to true

Above definition would allow fulltext query to be performed. But we can do more. Suppose you want to give more preference to those nodes where the fulltext term is found in jcr:title compared to any other field. In such cases we can boost such fields

  + indexRules
    - jcr:primaryType = "nt:unstructured"
    + app:Asset
      + properties
        - jcr:primaryType = "nt:unstructured"
        + comment
          - propertyIndex = true
          - nodeScopeIndex = true
          - name = "jcr:content/metadata/comment"
        + title
          - propertyIndex = true
          - nodeScopeIndex = true
          - name = "jcr:content/metadata/jcr:title"
          - boost = 2.0