Pivotal GemFire® v8.0

Creating Key Indexes

Creating Key Indexes

You can create key indexes by using the createKeyIndex method of the QueryService or by defining the index in cache.xml. Creating a key index makes the query service aware of the relationship between the values in the region and the keys in the region.

The FROM clause for a primary key index must be just a region path. The indexed expression is an expression that, when applied to an entry value, produces the key. For example, if a region has Portfolios as the values and the keys are the id field of the Portfolios region, the indexed expression is id.

Creating a key index is a good way to improve query performance when data is partitioned using a key or a field value. You can then use the FunctionService (using the partitioned key as a filter passed to the function and as part of the query equality condition) to execute the query against the indexed data. See Optimizing Queries on Data Partitioned by a Key or Field Value for more details.

There are two issues to note with key indexes:
  • The key index is not sorted. Without sorting, you can only do equality tests. Other comparisons are not possible. To obtain a sorted index on your primary keys, create a functional index on the attribute used as the primary key.
  • The query service is not automatically aware of the relationship between the region values and keys. For this, you must create the key index.
Note: Using a key-index with an explicit type='range' in the cache.xml will lead to an exception. Key indexes will not be used in 'range' queries.

Examples of Creating a Key Index

Using Java API:
QueryService qs = cache.getQueryService();
 qs.createKeyIndex("myKeyIndex", "id", "/exampleRegion");
Using gfsh:
gfsh> create index --name=myKeyIndex --expression=id --region=/exampleRegion
Using cache.xml:
<region name=exampleRegion>
 <region-attributes . . . >
 <index name="myKeyIndex" from-clause="/exampleRegion" expression="id" key-index="true"/>
Note: If you do not specify the type of index when defining indexes using cache.xml, the type defaults to "range".