8.4. Query and Export Commands

These commands are used to query and export simple features. Required parameters are indicated with a *.

8.4.1. convert

The convert command is used to directly transform data in one format into another, without ingesting them into GeoMesa. For example, it could be used to convert CSV files to GeoJSON.

Argument Description
-f, --feature-name The name of the schema
-s, --spec The SimpleFeatureType specification to create
-C, --converter The GeoMesa converter used to create SimpleFeatures
--converter-error-mode Override the error mode defined by the converter
-q, --cql CQL filter to select features to export
-m, --max-features Limit the number of features exported
-F, --output-format Output format used for export
-o, --output Output to a file instead of standard out
--input-format File format of input files (shp, csv, tsv, avro, etc)
--hints Query hints used to modify the query
--gzip Level of gzip compression to use for output, from 1-9
--no-header Don’t export the type header, for CSV and TSV formats
--force Force execution without prompt

See export and ingest for a description of the arguments.

8.4.2. explain

The explain command can be used to debug queries that are slow or problematic. Without actually running the query, it will show a variety of data, including the index being used, any query hints extracted, the exact ranges being scanned and filters being applied.

Argument Description
-c, --catalog * The catalog table containing schema metadata
-f, --feature-name * The name of the schema
-q, --cql * CQL filter to select features to export
-a, --attributes Specific attributes to export
--hints Query hints used to modify the query
--index Specific index used to run the query

See export for a description of the arguments.

8.4.3. export

Export features in a variety of formats.

See Moving and Migrating Data for details on how the export/import commands can be used to move data between clusters.

Argument Description
-c, --catalog * The catalog table containing schema metadata
-f, --feature-name * The name of the schema
-q, --cql CQL filter to select features to export
-a, --attributes Comma-separated list of attributes to export
--attribute Complex attribute transforms to export
-m, --max-features Limit the number of features exported
-F, --output-format Output format used for export
-o, --output Output to a file instead of standard out
--sort-by Sort by the specified attributes
--sort-descending Sort in descending order, instead of the default ascending order
--hints Query hints used to modify the query
--index Specific index used to run the query
--no-header For CSV and TSV formats, suppress the normal column headers
--gzip Level of gzip compression to use for output, from 1-9
--chunk-size Split the output into multiple files of the given size
--run-mode Run locally or as a distributed map/reduce job
--num-reducers Specify the number of reduces, when running in distributed mode
--force Force execution without prompts

The --attributes and --attribute parameters can be used to select a subset of attributes to export, or to transform the returned attributes using filter functions. A simple projection can be specified as a comma-delimited list:

--attributes name,age,geom

The feature ID can be specified along with other attribute names, with the reserved word id:

--attributes id,name,age,geom

Transforms can be accomplished by using --attribute to specify transform functions. Note that compared to --attributes, only a single argument can be specified per parameter, and commas will not be interpreted as a delimiter:

--attribute id --attribute name --attribute "name_transform=strConcat(name, 'foo')"

For a full list of transforms, see the GeoTools documentation. Note that not all functions work in transforms, however.

The --output-format argument defines the encoding used for export. Currently, it can be one of:

  • arrow Apache Arrow streaming file format
  • avro Apache Avro format
  • bin Custom minimal binary encoding
  • csv or tsv
  • json
  • gml or gml2 Geography Markup Language
  • html Export data to a Leaflet map and open in the default browser, if possible
  • orc Apache Orc files
  • parquet Apache Parquet files
  • shp ESRI Shapefile
  • null suppress output entirely

Note

The Leaflet format is intended for testing and small scale data exploration and visualization only. For production map generation it is highly recommended to use GeoServer. Additionally, the resulting file from this command requires the use of an online browser to open in order to access online resources.

The --output argument can be used to export to a file. By default, export data is written to standard output.

The --sort-by argument can be used to sort the output by one or more attributes. Note that for local exports, this will usually be done in-memory, so can be costly for large result sets. By default, output is sorted in ascending order; --sort-descending can be used to reverse the sort order.

The --hints argument can be used to set query hints. Hints should be specified as key1=value1;key2=value2, etc. Note that due to shell expansion, the hint string will likely need to be quoted. See Analytic Querying for examples of query hints that can be set. Note that query hints may cause errors if they don’t correspond to the output format specified.

The --index argument can be used to force the query to run against a particular index, instead of using the best index as determined through query planning. The argument should be the name of an index, e.g. id or z3. See Index Overview for a list of valid indices. Note that not all schemas will have all index types.

The --gzip argument can be used to compress the output through gzip encoding. It can be specified as a number between 1-9. Higher numbers indicate more compression, lower numbers indicate faster compression.

The --chunk-size argument can be used to split the output into multiple smaller files. It is specified as a size in bytes, e.g. 10MB. Note that due to buffering and metadata, it is generally not feasible to hit the chunk size exactly. For finer control, the system property org.locationtech.geomesa.export.bytes-per-feature can be used to set an initial number of bytes per feature as a float, i.e. 5.5. If exporting to multiple formats at once, the property org.locationtech.geomesa.export.<name>.bytes-per-feature can also be used, where <name> corresponds to one of the output formats mentioned above (e.g. json, parquet, etc).

The --run-mode distributed argument can be used to specify a distributed map/reduce export, for data stores that support it. Distributed exports can be used for data migration or large-scale sorting. When running in distributed mode, the output file must be in a distributed filesystem (e.g. HDFS or S3). When sorting a distributed export, --num-reducers must be specified to set the number of reducer tasks.

The --force argument can be used to suppress prompts, such as a prompt to overwrite an existing file. This should be used with care, as data loss can occur if you export to an existing directory.

8.4.4. playback

The playback command can simulate a streaming ingestion by replaying features that have already been ingested. Features are returned based on a date attribute in the feature. For example, if replaying three features that have dates that are each one second apart, each feature will be emitted after a delay of one second. The rate of export can be modified to speed up or slow down the original time differences.

In order to simulate a data stream, the output of this command can be piped into another process, for example to send messages to a Kafka topic or write files to NiFi for ingestion.

Argument Description
-c, --catalog * The catalog table containing schema metadata
-f, --feature-name * The name of the schema
--interval * Date interval to replay, in the format yyyy-MM-dd'T'HH:mm:ss.SSSZ/yyyy-MM-dd'T'HH:mm:ss.SSSZ
--dtg Date attribute to base playback on. If not specified, will use the default schema date field
--rate Rate multiplier to speed-up (or slow down) features being returned, as a float
--step-window Query the interval in discrete chunks instead of all at once (‘10 minutes’, ‘30 seconds’, etc)
-q, --cql Additional CQL filter to select features to export. Features will automatically be filtered to match the time interval
-a, --attributes Specific attributes to export
-m, --max-features Limit the number of features exported
-F, --output-format Output format used for export
-o, --output Output to a file instead of standard out
--hints Query hints used to modify the query
--no-header Don’t export the type header, for CSV and TSV formats
--gzip Level of gzip compression to use for output, from 1-9

The playback command is an extension of the export command, and accepts all the parameters outlined there.

The --interval parameter specifies the date range for features to replay, based on the date attribute specified by --dtg, or the default schema date attribute if not specified.

The --rate parameter can be used to speed up or slow down the replay. It is specified as a floating point number. For example --rate 10 will make replay ten times faster, while --rate 0.1 will make replay ten times slower.

The --step-window parameter can be used to break up the query into discrete chunks, based on the time interval. For larger exports, this will save memory overhead when sorting and will likely be faster. The window should be large enough so that the overhead of creating multiple queries doesn’t slow down the process, but small enough so that a manageable batch of features is returned for each query. The optimal window size will depend on the time-based density of features, and the available hardware.