This topic explains how to create indexes on Map Fields in VMware Tanzu GemFire.
To assist with the quick lookup of multiple values in a Map (or HashMap) type field, you can create an index (or “map index”) on specific or all keys in that field.
For example, you could create a map index to support the following query:
SELECT * FROM /users u WHERE u.name['first'] = 'John' OR u.name['last'] = 'Smith'
The map index extends regular range indexes created on single key by maintaining indexes for other specified keys, or for all keys if * is used. The underlying structure of the map index can be thought of as a wrapper around all these indexes.
The following Java code samples provide examples of how to create a map index:
QueryService qs = cache.getQueryService();
//This will create indexes for for keys 'PVTL' and 'VMW'
qs.createIndex("indexName", "p.positions['PVTL', 'VMW']", "/portfolio p");
QueryService qs = cache.getQueryService();
//This will create indexes for all keys
qs.createIndex("indexName", "p.positions[*]", "/portfolio p");
In gfsh, the equivalents are:
gfsh>create index --name="IndexName" --expression="p.positions['PVTL', 'VMW']" --region="/portfolio p" --type=range
gfsh>create index --name="IndexName" --expression="p.positions[*]" --region="/portfolio p" --type=range
To create or query a map index, you must use the bracket notation to list the map field keys you wish to index or query. For example: [*], ['keyX1','keyX2']. Note that using p.pos.get('keyX1') will not create or query the map index.
Note: You can still query against Map or HashMap fields without querying against a map index. For example, you can always create a regular range query on a single key in any Map or HashMap field. However, note that subsequent query lookups will be limited to a single key.
Note: Map indexes on all keys (when * is specified) are not used in queries where the map field is compared with null or when it is compared using !=, e.g. p.positions['company1'] = null or p.positions['company1'] != '3'. These types of queries will be executed without making use of the index, which could make them slower.
