6.3. Index Basics¶

GeoMesa will create various indices for a given SimpleFeatureType schema (see Index Overview). This allows us to answer a variety of queries in a optimized manner. GeoMesa will make a best effort to determine the attributes used for indexing. The attributes to use can also be specified as part of the SimpleFeatureType.

6.3.1. Spatial Index (Z2/XZ2)¶

If the SimpleFeatureType has a Geometry-type attribute (Point, LineString, Polygon, etc), GeoMesa will create a spatial index on that attribute. If there is more than one Geometry-type attribute, the default one will be used. The default geometry is generally specified with a * prefix in the SimpleFeatureType string, and is the one returned by SimpleFeatureType.getGeometryDescriptor.

6.3.2. Spatio-temporal Index (Z3/XZ3)¶

If the SimpleFeatureType has both a Geometry-type attribute and a Date attribute, GeoMesa will create a spatio-temporal index on those attributes. The Geometry-type attribute used is the same as for the spatial index, above. The Date attribute selected will be the first one declared, or can be set explicitly. See Setting the Indexed Date Attribute for details on setting the indexed date.

6.3.3. ID Index¶

GeoMesa will always create an ID index on SimpleFeature.getID().

6.3.4. Attribute Index¶

Some queries are slow to answer using the default indices. For example, with twitter data you might want to return all tweets for a given user. To speed up this type of query, any attribute in your simple feature type may be indexed individually.

To index an attribute, add an index key to the attribute descriptor user data with a value of true.

Note

Accumulo data stores have an additional option to create reduced ‘join’ attribute indices, which can save space. See Accumulo Attribute Indices for details.

SimpleFeatureType sft = ...
sft.getDescriptor("name").getUserData().put("index", "true");

import org.locationtech.geomesa.utils.geotools.SchemaBuilder

val sft = SchemaBuilder.builder()
    .addString("name").withIndex()
    .addDate("dtg")
    .addPoint("geom", default = true)
    .build("mySft")

Setting the user data can be done in multiple ways. See Setting Schema Options for more details.

To prioritize certain attributes over others, see Cardinality Hints.

6.4. Index Versioning¶

In order to ensure cross-compatibility, each index created by GeoMesa has a version number that identifies the layout of data on disk, which is fixed at the time of creation. Updating GeoMesa versions will provide bug fixes and new features, but will not update existing data to new index formats.

The exact version of an index used for each schema can be read from the SimpleFeatureType user data, or by simple examining the name of the index tables created by GeoMesa. The particular version numbers vary across the different back-end implementations. See Accumulo Index Versions, HBase Index Versions and Cassandra Index Versions for the differences between index versions.