6.2. Index Configuration

GeoMesa exposes a variety of configuration options that can be used to customize and optimize a given installation.

6.2.1. Setting Schema Options

Static properties of a SimpleFeatureType must be set when calling createSchema, and can’t be changed afterwards. Most properties are controlled through user-data values, either on the SimpleFeatureType or on a particular attribute. Setting the user data can be done in multiple ways.

If you are using a string to indicate your SimpleFeatureType (e.g. through the command line tools, or when using SimpleFeatureTypes.createType), you can append the type-level options to the end of the string, like so:

// append the user-data hints to the end of the string, separated by a semi-colon
String spec = "name:String,dtg:Date,*geom:Point:srid=4326;option.one='foo',option.two='bar'";
SimpleFeatureType sft = SimpleFeatureTypes.createType("mySft", spec);

If you have an existing simple feature type, or you are not using SimpleFeatureTypes.createType, you may set the hints directly in the feature type:

// set the hint directly
SimpleFeatureType sft = ...
sft.getUserData().put("option.one", "foo");

If you are using TypeSafe configuration files to define your simple feature type, you may include a ‘user-data’ key:

geomesa {
  sfts {
    "mySft" = {
      attributes = [
        { name = name, type = String             }
        { name = dtg,  type = Date               }
        { name = geom, type = Point, srid = 4326 }
      ]
      user-data = {
        option.one = "foo"
      }
    }
  }
}

6.2.2. Customizing Index Creation

To speed up ingestion, or because you are only using certain query patterns, you may disable some indices. The indices are created when calling createSchema. If nothing is specified, the Z2/Z3 (or XZ2/XZ3 depending on geometry type) indices and record indices will all be created, as well as any attribute indices you have defined.

Warning

Certain queries may be much slower if you disable an index.

To enable only certain indices, you may set a hint in your simple feature type. The hint key is geomesa.indexes.enabled, and it should contain a comma-delimited list containing a subset of:

  • z2 - corresponds to the Z2 index
  • z3 - corresponds to the Z3 index
  • records - corresponds to the id/record index (for Accumulo data stores)
  • id - corresponds to the id/record index (for non-Accumulo data stores)
  • attr - corresponds to the attribute index

You may set the hint using Setting Schema Options. If you are using the GeoMesa SftBuilder, you may instead call the withIndexes methods:

// scala example
import org.locationtech.geomesa.utils.geotools.SftBuilder.SftBuilder

val sft = new SftBuilder()
    .stringType("name")
    .date("dtg")
    .geometry("geom", default = true)
    .withIndexes(List("records", "z3", "attr_idx"))
    .build("mySft")

6.2.3. Configuring Z-Index Shards

GeoMesa allows configuration of the number of shards (or splits) into which the Z2/Z3/XZ2/XZ3 indices are divided. This parameter may be changed individually for each SimpleFeatureType. If nothing is specified, GeoMesa will default to 4 shards. The number of shards must be between 1 and 127.

Shards allow us to pre-split tables, which provides some initial parallelism for reads and writes. As more data is written, tables will generally split based on size, thus obviating the need for explicit shards. For small data sets, shards are more important as the tables might never split due to size. Setting the number of shards too high can reduce performance, as it requires more calculations to be performed per query.

The number of shards is set when calling createSchema. It may be specified through the simple feature type user data using the hint geomesa.z.splits. See Setting Schema Options.

sft.getUserData().put("geomesa.z.splits", "4");

6.2.4. Configuring Z-Index Time Interval

GeoMesa uses a z-curve index for time-based queries. By default, time is split into week-long chunks and indexed per week. If your queries are typically much larger or smaller than one week, you may wish to partition at a different interval. GeoMesa provides four intervals - day, week, month or year. As the interval gets larger, fewer partitions must be examined for a query, but the precision of each interval will go down.

If you typically query months of data at a time, then indexing per month may provide better performance. Alternatively, if you typically query minutes of data at a time, indexing per day may be faster. The default per week partitioning tends to provides a good balance for most scenarios. Note that the optimal partitioning depends on query patterns, not the distribution of data.

The time partitioning is set when calling createSchema. It may be specified through the simple feature type user data using the hint geomesa.z3.interval. See Setting Schema Options.

sft.getUserData().put("geomesa.z3.interval", "month");

6.2.5. Configuring XZ-Index Precision

GeoMesa uses an extended z-curve index for storing geometries with extents. The index can be customized by specifying the resolution level used to store geometries. By default, the resolution level is 12. If you have very large geometries, you may want to lower this value. Conversely, if you have very small geometries, you may want to raise it.

The resolution level for an index is set when calling createSchema. It may be specified through the simple feature type user data using the hint geomesa.xz.precision. See Setting Schema Options.

sft.getUserData().put("geomesa.xz.precision", 12);

For more information on resolution level (g), see “XZ-Ordering: A Space-Filling Curve for Objects with Spatial Extension” by Böhm, Klump and Kriegel.

6.2.6. Mixed Geometry Types

A common pitfall is to unnecessarily specify a generic geometry type when creating a schema. Because GeoMesa relies on the geometry type for indexing decisions, this can negatively impact performance.

If the default geometry type is Geometry (i.e. supporting both point and non-point features), you must explicitly enable “mixed” indexing mode. Any other geometry type (Point, LineString, Polygon, etc) are not affected.

Mixed geometries must be declared when calling createSchema. It may be specified through the simple feature type user data using the hint geomesa.mixed.geometries. See Setting Schema Options.

sft.getUserData().put("geomesa.mixed.geometries", "true");