CORAL WIKI

Actors

CassandraActor
FilterActor
FsmActor
GeneratorActor
GroupByActor
HttpBroadcastActor
HttpClientActor
JsonActor
KafkaConsumerActor
KafkaProducerActor
LinearRegressionActor
LogActor
LookupActor
SampleActor
StatsActor
ThresholdActor
WindowActor
ZscoreActor

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Overview

Actors
Architecture
Coral streaming analytics
Metrics
Why Coral?

CassandraActor

The CassandraActor is a Coral Actor that enables communication with a Cassandra database. The actor receives queries in the trigger field and emits the results. All valid CQL queries can be executed, including creating keyspaces and inserting, deleting and updating values.

Creating a CassandraActor

The creation JSON of the CassandraActor (see Coral Actor) has "type": "cassandra". The params value is a JSON with the following fields:

field type required description
seeds List[String] yes A JSON list of the IP addresses of seed nodes
keyspace String yes The name of the keyspace to connect to initially
port Int no The port to connect to, when omitted the default Cassandra port is used

Creation example

{
  "data": {
      "type": "actors",
      "attributes": {
        "type": "cassandra",
        "params": {
          "seeds": ["10.0.0.1", "10.0.0.2"],
          "keyspace": "keyspacename"
        |
      }
  }
}

This will create a CassandraActor connecting to any of the nodes 10.0.0.1 or 10.0.0.2 to keyspace “keyspacename”.

Trigger

The CassandraActor receives the CQL statement in the query field of the trigger JSON.

Example

{
    "query":"select * from testkeyspace.test1"
}

Emit

The CassandraActor emits a JSON object which format depends on the type of query and the result of the query.

Query with a result set

When a query has a result set, the emitted JSON has the following fields:

field description
query The executed query
success true when the query was successful
columns the columns of the result with the types
data the result set of the query

Query without result set

When a query doesn’t have a result set (e.g. a delete query) only the query and success fields are present in the emitted JSON.

Query with an error

When a query can’t be executed due to an error, the emitted JSON has the following fields:

field description
query The executed query
success false when the query was not successful
error the error message

Example

When a query has results, the JSON has the following format:

{
    "query": "select * from testkeyspace.test1",
    "success": true,
    "columns": [{
        "col1": "varchar"
    },{
        "col2": "int"
    },{
        "col3": "float"
    }], "data": [
        [ "abc", 42, 57.6609992980957 ],
        [ "stuff", 48, 25.6299991607666 ],
        [ "blabla", 10, 34.19839859008789 ]
    ]
}"

State

The CassandraActor returns its state as follows:

field type description
connected boolean Whether there is still an active connection to the Cassandra database at the time of collecting the state.
keyspace String The name of the keyspace the actor is currently connected to.
schema Array A JSON representation of the schema of the keyspace currently connected to.

An example of a schema is as follows:

{
  "connected": true,
  "keyspace": "keyspacename",
  "schema": [{
    "table1": [
     { "column1": "text" },
     { "column2": "int" },
     { "column3": "float" }], 
    "table2": [
     { "col1": "float" },
     { "col2": "int" }]
  }]
}

Collect

The CassandraActor does not collect state from other actors.

Timer

The CassandraActor does not provide timer actions.