14.8. Data Management

GeoMesa provides many ways to optimize your data storage. You can add additional indices to speed up certain queries, disable indices to speed up ingestion, pre-split tables for optimal data distribution and migrate data between tables or environments.

14.8.1. Accumulo Attribute Indices

See Attribute Index for an overview of attribute indices. The Accumulo data store extends the normal attribute indices with an additional ‘join’ format that stores less data.

14.8.1.1. Join Indices

Join indices store a reduced subset of data in the index - just the feature ID, the default date and the default geometry. To answer most queries, a join against the record index is required to retrieve the full simple features - hence the name join index. Joining against the record table is slow when returning many results, and should generally be avoided except for small queries.

GeoMesa will avoid joining against the record table if it is possible to answer a query with only the data in the join index. In general, this means that the query is only returning the properties for the default date, default geometry and the attribute being queried. In addition, any CQL filters must only operate on those three attributes as well.

To enable a join index, the keyword join may be used in place of true when specifying an attribute index in the SimpleFeatureType.

14.8.1.2. Full Indices

Full indices store the full simple feature. This takes up the most space on disk, but allows for any query to be answered without joining against the record table. This is the only option for non-Accumulo data stores. To use a full index, the keyword full or true may be used when specifying an attribute index in the SimpleFeatureType.

14.8.2. Accumulo Logical Timestamps

By default, GeoMesa index tables are created using Accumulo’s logical time. This ensures that updates to a given simple feature will be ordered correctly, however it obscures the actual insert time for the underlying data row. For advanced use cases, standard system time can be used instead of logical time. To disble logical time, add the following user data hint to the simple feature type before calling createSchema:

// append the hints to the end of the string, separated by a semi-colon
String spec = "name:String,dtg:Date,*geom:Point:srid=4326;geomesa.logical.time='false'";
SimpleFeatureType sft = SimpleFeatureTypes.createType("mySft", spec);

14.8.3. Upgrading Existing Indices

GeoMesa often makes updates to indexing formats to improve query and write performance. However, the index format for a given schema is fixed when it is first created. 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. See below for a description of current index versions.

Using the GeoMesa command line tools, you can add or update an index to a newer version using add-index. For example, you could add the XZ3 index to replace the Z3 index for a feature type with non-point geometries. The command will populate the new index using a distributed job. For large data sets, you can choose to only populate features matching a CQL filter (e.g. the last month), or choose to not populate any data. The update is seamless, and clients can continue to query and ingest while it runs.

See add-index for more details on the command line tools.