HashIndex plug-in attributes

Attributes

Name

Specifies the name of the index. The name must be unique for each map. The name is used to retrieve the index object from the object map instance for the backing map.

AttributeName

Specifies the comma-delimited names of the attributes to index. For field-access indexes, the attribute names are equivalent to the field names. For property-access indexes, the attribute names are the JavaBean compatible property names. If only one attribute name exists, the HashIndex is a single attribute index. If this attribute is a relationship, it is also a relationship index. If multiple attribute names are included in the attribute names, the HashIndex is a composite index.

FieldAccessAttribute

Used for non-entity maps. If true, the object is accessed using the fields directly. If not specified or false, the getter method for the attribute is used to access the data.

GlobalIndexEnabled

If set to true, global index is enabled and the application can cast the retrieved index object to the MapGlobalIndex interface.

When the GlobalIndexEnabled property of HashIndex is set to true, the global index function of HashIndex is enabled to support the MapGlobalIndex interface on top of any HashIndex configuration. It provides an efficient way to find data in large partitioned environment.

The following example shows that global index is enabled on a single-attribute HashIndex:

<bean id="MapIndexPlugin" 
      className="com.ibm.websphere.objectgrid.plugins.index.HashIndex">
         <property name="Name" type="java.lang.String" value="CODE" 
            description="index name" />
         <property name="AttributeName" type="java.lang.String" value="employeeCode" 
            description="attribute name" />
 	<property name="GlobalIndexEnabled" type="boolean" value="true" 
            description="true for global index" />
   </bean>

GlobalIndexSyncUpdate

The GlobalIndexSyncUpdate property setting takes effect when GlobalIndexEnabled property is set to true. If GlobalIndexSyncUpdate property is set to true, the global index update process is synchronous to HashIndex update that is part of user transaction and has impact on the performance of write transactions that cause index structure change. Application should only consider to set GlobalIndexSyncUpdate property to true when it expects global index look ups always returns up-to-date committed data.

POJOKeyIndex

Used for non-entity maps. If true, the index introspects the object in the key part of the map. This setting is useful when the key is a composite key and the value does not have the key embedded within it. If not specified or false, then the index introspects the object in the value part of the map.

RangeIndex

If true, range indexing is enabled and the application can cast the retrieved index object to the MapRangeIndex interface. If the RangeIndex property is configured as false, the application can cast the retrieved index object to the MapIndex interface only.

Single-attribute HashIndex versus composite HashIndex

When the AttributeName property of HashIndex includes multiple attribute names, the HashIndex is a composite index. Otherwise, if it includes only one attribute name, it is a single-attribute index. For example, the AttributeName property value of a composite HashIndex might be city,state,zipcode. It includes three attributes delimited by commas. If the AttributeName property value is only zipcode that only has one attribute, it is a single-attribute HashIndex.

Composite HashIndex provides an efficient way to look up cached objects when search criteria involve many attributes. However, it does not support range index and its RangeIndex property must set to false.

For more information, see Using a composite index.

Relationship HashIndex

If the indexed attribute of single-attribute HashIndex is a relationship, either single- or multi-valued, the HashIndex is a relationship HashIndex. For relationship HashIndex, the RangeIndex property of HashIndex must set to “false”.

Relationship HashIndex can speed up queries that use cyclical references or use the IS NULL, IS EMPTY, SIZE, and MEMBER OF query filters. For more information, see Query optimization using indexes.

Key HashIndex

For non-entity maps, when the POJOKeyIndex property of HashIndex is set to true, the HashIndex is a key HashIndex and the key part of entry are used for indexing. When the AttributeName property of HashIndex is not specified, the whole key is indexed; otherwise, the key HashIndex can only be a single-attribute HashIndex.

For example, adding the following property into the preceding sample causes the HashIndex to become key HashIndex because the POJOKeyIndex property value is true.

<property name="POJOKeyIndex" type="boolean" value="true" 
description="indicates if POJO key HashIndex" />

In the preceding key index example, because the AttributeName property value is specified as employeeCode, the indexed attribute is the employeeCode field of the key part of map entry. If you want to build key index on the whole key part of map entry, remove the AttributeName property.

Range HashIndex

When the RangeIndex property of HashIndex is set to true, the HashIndex is a range index and can support the MapRangeIndex interface. A MapRangeIndex implementation supports functions to find data using range functions, such as greater than, less than, or both, while a MapIndex supports equals functions only. For a single-attribute index, the RangeIndex property can be set to true only if the indexed attribute is of type Comparable. If the single-attribute index will be used by query, the RangeIndex property must set to true and the indexed attribute must be of type Comparable. For relationship HashIndex and composite HashIndex, the RangeIndex property must set to false.

The preceding sample is a range HashIndex because the RangeIndex property value is true.

The following table provides a summary for using range index.

Query optimization with HashIndex plug-ins

Defining indexes can significantly improve query performance.WebSphere® eXtreme Scale queries can use built-in HashIndex plug-ins to improve performance of queries. Although using indexes can significantly improve query performance, it might have a performance impact on transactional map operations.