18.2. Using the Kafka Data Store Programmatically¶

18.2.1. Creating a Data Store¶

An instance of a Kafka data store can be obtained through the normal GeoTools discovery methods, assuming that the GeoMesa code is on the classpath. To create a KafkaDataStore there are two required properties, one for the Apache Kafka connection, kafka.brokers, and one for the Apache Zookeeper connection, kafka.zookeepers. An optional parameter, kafka.zk.path is used to specify a path in Zookeeper under which schemas are stored. If no zk path is specified then a default path will be used. Configuration parameters are described fully below.

import org.geotools.data.DataStore;
import org.geotools.data.DataStoreFinder;

Map<String, Serializable> parameters = new HashMap<>();
parameters.put("kafka.zookeepers", "localhost:2181");
parameters.put("kafka.brokers", "localhost:9092");
DataStore dataStore = DataStoreFinder.getDataStore(parameters);

18.2.2. Kafka Data Store Parameters¶

The Kafka data store differs from most data stores in that the data set is kept entirely in memory. Because of this, the in-memory indexing can be configured at runtime through data store parameters. See Kafka Index Configuration for more information on the available indexing options.

Because configuration options can reference attributes from a particular SimpleFeatureType, it may be necessary to create multiple Kafka data store instances when dealing with multiple schemas.

The Kafka data store accepts the following parameters (required parameters are marked with *):

Parameter	Type	Description
`kafka.brokers *`	String	Kafka brokers, e.g. “localhost:9092”
`kafka.zookeepers *`	String	Kafka zookeepers, e.g “localhost:2181”
`kafka.zk.path`	String	Zookeeper discoverable path, can be used to effectively namespace feature types
`kafka.producer.config`	String	Configuration options for kafka producer, in Java properties format. See Producer Configs
`kafka.producer.clear`	Boolean	Send a ‘clear’ message on startup. This will cause clients to ignore any data that was in the topic prior to startup
`kafka.consumer.config`	String	Configuration options for kafka consumer, in Java properties format. See Consumer Configs
`kafka.consumer.read-back`	String	On start up, read messages that were written within this time frame (vs ignore old messages), e.g. ‘1 hour’. Use ‘Inf’ to read all messages. If enabled, features will not be available for query until all existing messages are processed. However, feature listeners will still be invoked as normal. See Initial Load (Replay)
`kafka.consumer.count`	Integer	Number of kafka consumers used per feature type. Set to 0 to disable consuming (i.e. producer only)
`kafka.consumer.start-on-demand`	Boolean	The default behavior is to start consuming a topic only when that feature type is first requested. This can reduce load if some layers are never queried. Note that care should be taken when setting this to false, as the store will immediately start consuming from Kafka for all known feature types, which may require significant memory overhead.
`kafka.topic.partitions`	Integer	Number of partitions to use in new kafka topics
`kafka.topic.replication`	Integer	Replication factor to use in new kafka topics
`kafka.serialization.type`	String	Internal serialization format to use for kafka messages. Must be one of `kryo` or `avro`
`kafka.cache.expiry`	String	Expire features from in-memory cache after this delay, e.g. “10 minutes”. See Feature Expiration
`kafka.cache.expiry.dynamic`	String	Expire features dynamically based on CQL predicates. See Feature Expiration
`kafka.cache.event-time`	String	Instead of message time, determine expiry based on feature data. See Feature Event Time
`kafka.cache.event-time.ordering`	Boolean	Instead of message time, determine feature ordering based on the feature event time. See Feature Event Time
`kafka.index.cqengine`	String	Use CQEngine-based attribute indices for the in-memory feature cache. See CQEngine Indexing
`kafka.index.resolution.x`	Integer	Number of bins in the x-dimension of the spatial index, by default 360. See Spatial Index Resolution
`kafka.index.resolution.y`	Integer	Number of bins in the y-dimension of the spatial index, by default 180. See Spatial Index Resolution
`kafka.index.tiers`	String	Number and size of tiers used for indexing geometries with extents, in the form `x1:y1,x2:y2`. See Spatial Index Tiering
`kafka.serialization.lazy`	Boolean	Use lazy deserialization of features. This may improve processing load at the expense of slightly slower query times
`kafka.layer.views`	String	Additional views on existing schemas to expose as layers. See Layer Views for details
`kafka.metrics.reporters`	String	Reporters used to publish Kafka metrics, as TypeSafe config. To use multiple reporters, nest them under the key `reporters`. See GeoMesa Metrics for details
`geomesa.query.loose-bounding-box`	Boolean	Use loose bounding boxes, which offer improved performance but are not exact
`geomesa.query.audit`	Boolean	Audit incoming queries. By default audits are written to a log file
`geomesa.security.auths`	String	Default authorizations used to query data, comma-separated

More information on using GeoTools can be found in the GeoTools user guide.