NGSIArcgisFeatureTableSink
Content:
Functionality
com.iot.telefonica.cygnus.sinks.NGSIArcgisFeatureTableSink is a sink designed to persist NGSI-like context data events within an [ArcGis] (https://www.arcgis.com/home/index.html) feature table. Usually, such a context data is notified by a Orion Context Broker instance, but could be any other system speaking NGSI language.
Independently of the data generator, NGSI context data is always transformed into internal NGSIEvent objects at Cygnus sources. In the end, the information within these events must be mapped into specific ArcGis structures.
Next sections will explain this in detail.
Mapping NGSI events to NGSIEvent objects
Notified NGSI events (containing context data) are transformed into NGSIEvent objects (for each context element a NGSIEvent is created; such an event is a mix of certain headers and a ContextElement object), independently of the NGSI data generator or the final backend where it is persisted.
This is done at the cygnus-ngsi Http listeners (in Flume jergon, sources) thanks to NGSIRestHandler. Once translated, the data (now, as NGSIEvent objects) is put into the internal channels for future consumption (see next section).
Mapping NGSIEvents to ArcGis
ArcGis stores data in it's own databases using it's own data organization, you can checkout this info Reading Feature Table details at Argis server, Such organization is exploited by NGSIArcgisFeatureTableSink each time a NGSIEvent is going to be persisted.
Argis feature tables must be provisioned before sending entities.
ArcGis databases naming conventions
Each entity type needs an url and an unique field to be persisted into the feature table.
NGSIArcgisFeatureTableSink composes each table's url with entitie's service and service path, to provide multiple tables access.
Unique field is provided to allow NGSIArcgisFeatureTableSink to update existant entities. NGSI entity type will be used as unique field name.
All this parameters, can be customized using Cygnus mapping capabilities.
Let's see an example:
Agent.conf file:
agent.arcgis-sink.arcgis_service_url = https://arcgis.com/{hash}/arcgis/rest/services
Entity data:
service = vehicles
service-path = /4wheels
entity-type = car
result
Feature table url: https://arcgis.com/{hash}/arcgis/rest/services/vehicles/4wheels
Table's unique field: car
Example
NGSIEvent
Assuming the following NGSIEvent is created from a notified NGSI context data (the code below is an object representation, not any real data format):
ngsi-event={
headers={
content-type=application/json,
timestamp=1429535775,
transactionId=1429535775-308-0000000000,
correlationId=1429535775-308-0000000000,
fiware-service=vehicles,
fiware-servicepath=/4wheels,
<grouping_rules_interceptor_headers>,
<name_mappings_interceptor_headers>
},
body={
entityId=car1,
entityType=car,
attributes=[
{
attrName=speed,
attrType=float,
attrValue=112.9
},
{
attrName=oil_level,
attrType=float,
attrValue=74.6
}
]
}
}
Resultant service url:
https://arcgis.com/{hash}/arcgis/rest/services/vehicles/4wheels
Feature table unique field:
Unique field name: car
Unique field value: car1
Administration guide
Configuration
NGSIArcgisFeatureTableSink is configured through the following parameters:
| Parameter | Mandatory | Default value | Comments |
|---|---|---|---|
| type | yes | N/A | Must be com.telefonica.iot.cygnus.sinks.NGSIArcgisFeatureTableSink |
| channel | yes | N/A | |
| enable_encoding | no | false | true or false, true applies the new encoding, false applies the old encoding. |
| enable_grouping | no | false | true or false. Check this link for more details. |
| enable_name_mappings | no | false | true or false. Check this link for more details. |
| arcgis_service_url | yes | N/A | https://{url_host}/{id_arcgis}/arcgis/rest/services |
| arcgis_username | yes | N/A | |
| arcgis_password | yes | N/A | |
| arcgis_gettoken_url | yes | N/A | https://{url_host}/sharing/generateToken |
| arcgis_maxBatchSize | no | 10 | Number of events accumulated before persistence. |
| batch_timeout | no | 30 | Number of seconds the batch will be building before it is persisted as it is. |
| batch_ttl | no | 10 | Number of retries when a batch cannot be persisted. Use 0 for no retries, -1 for infinite retries. Please, consider an infinite TTL (even a very large one) may consume all the sink's channel capacity very quickly. |
A configuration example could be:
cygnus-ngsi.sinks = arcgis-sink
cygnus-ngsi.channels = arcgis-channel
...
cygnus-ngsi.sinks.arcgis-sink.type = com.telefonica.iot.cygnus.sinks.NGSIArcgisFeatureTableSink
cygnus-ngsi.sinks.arcgis-sink.channel = arcgis-channel
cygnus-ngsi.sinks.arcgis-sink.enable_name_mappings = true
cygnus-ngsi.sinks.arcgis-sink.enable_name_mappings = false
cygnus-ngsi.sinks.arcgis-sink.arcgis_service_url = https://arcgis.com/UsuarioArcgis/arcgis/rest/services
cygnus-ngsi.sinks.arcgis-sink.arcgis_username = myuser
cygnus-ngsi.sinks.arcgis-sink.arcgis_password = mypassword
cygnus-ngsi.sinks.arcgis-sink.arcgis_gettoken_url = https://arcgis.com/sharing/generateToken
cygnus-ngsi.sinks.arcgis-sink.arcgis_maxBatchSize = 10
Important notes
About batching
As explained in the programmers guide, NGSIArcgisFeatureTableSink extends NGSISink, which provides a built-in mechanism for collecting events from the internal Flume channel. This mechanism allows extending classes have only to deal with the persistence details of such a batch of events in the final backend.
What is important regarding the batch mechanism is it largely increases the performance of the sink, because the number of writes is dramatically reduced. Let's see an example, let's assume a batch of 10 NGSIEvents. In the best case, all these events regard to the same type of entity, which means all the data within them will be persisted in the same ArcGis layer. If processing the events one by one, we would need 10 inserts into ArcGis; nevertheless, in this example only one insert is required. Obviously, not all the events will always regard to the same unique type of entity, and many entities may be involved within a batch.
The batch mechanism adds an accumulation timeout to prevent the sink stays in an eternal state of batch building when no new data arrives. If such a timeout is reached, then the batch is persisted as it is.
Regarding the retries of not persisted batches, a couple of parameters is used. On the one hand, a Time-To-Live (TTL) is used, specifing the number of retries Cygnus will do before definitely dropping the event. On the other hand, a list of retry intervals can be configured. Such a list defines the first retry interval, then se second retry interval, and so on; if the TTL is greater than the length of the list, then the last retry interval is repeated as many times as necessary.
By default, NGSIArcgisFeatureTableSink has a configured batch size and batch accumulation timeout of 1 and 30 seconds, respectively. Nevertheless, as explained above, it is highly recommended to increase at least the batch size for performance purposes. Which are the optimal values? The size of the batch it is closely related to the transaction size of the channel the events are got from (it has no sense the first one is greater then the second one), and it depends on the number of estimated sub-batches as well. The accumulation timeout will depend on how often you want to see new data in the final storage. A deeper discussion on the batches of events and their appropriate sizing may be found in the performance document.
Connections to cygnus-ngsi.sinks.arcgis-sink.arcgis_service_url and cygnus-ngsi.sinks.arcgis-sink.arcgis_service_url are done without check certificate validation of Java SSL Connections.
Programmers guide
NGSIArcgisFeatureTableSink class
As any other NGSI-like sink, NGSIArcgisFeatureTableSink extends the base NGSISink. The methods that are extended are:
void persistBatch(NGSIBatch batch) throws CygnusBadConfiguration,
CygnusBadContextData, CygnusRuntimeError, CygnusPersistenceError;
A Batch contains a set of NGSIEvent objects, which are the result of parsing the notified context data events. Data within the batch is classified by destination, and in the end, a destination specifies the ArcGis where the data is going to be persisted. Thus, each destination is iterated in order to compose a per-destination data string to be persisted thanks to any Arcgis implementation.
public void start();
This must be done at the start() method and not in the constructor since the invoking sequence is NGSIArcgisFeatureTableSink() (contructor), configure() and start().
public void configure(Context);
A complete configuration as the described above is read from the given Context instance.
Authentication and authorization
Current implementation of NGSIArcgisFeatureTableSink relies on the username and password credentials created at the ArcGis endpoint.