Websocket Spec

Data Access - Query Data via SQL

A WebSocket allows the client to request data using SQL as input.

Use the following URL to open a WebSocket connection. Depending on deployment, use ws (not-secure) or wss (secure) connection:

WS | WSS ${LENSES_URL}/api/ws/v2/sql/execute

Once the connection is established, the server expects the client to send a JSON message with the following structure:

{
  "token": String,
  "sql": String,
  "live": Optional[Boolean],
  "stats": Optional[Int]
}

Field	Description	Type
token	How often to refresh kafka topic list and configs	long
sql	The SQL query used to fetch data	string
live	If set, enables partial results for aggregation queries.	optional[boolean]
stats	Millis interval to receive query stats. If not provided the stats information is not sent	optional[int]

The client should wait for incoming messages and stop when EOF is received. The server sends JSON-encoded messages, the payload structure is:

{
  "type": <Enumeration>,
  "data": <Dependent on the type field>
}

Since there are multiple types of messages the server sends, the type attribute determines the data structure for the data payload. Below is the list of possible type values:

Value	Description
HEARTBEAT	To keep the connection alive, the server injects an empty message.
RECORD	The message represents a data record.
ERROR	The message contains information about an error that occurred.
STATS	The message contains information about the current execution.Only activated if the stats field in the request is present.
METADATA	The message contains a list of metadata fields each record message will contain. For example: offset, partition,timestamp, __keysize, __valueSize, valueSchemaId.
SCHEMA	Reserved.
PAGE_END	Reserved.
END	The message signals the end of the execution. The server will close the socket after this message is sent.
BADRECORD	The message contains information about the Kafka message which cannot be read. For example, if the topic expects Avro and the payload is not a valid Avro.
SENTINEL	The message contains information about the execution termination reason when query thresholds are reached.

Message types

Heartbeat

The data the attribute is null. The client should ignore these messages.

{
  "type": "HEARTBEAT"
}

Error

In this case, the payload structure is:

{
  "type": "HEARTBEAT",
  "data": String
}

Stats

When requested the payload format is:

{
  "type": "HEARTBEAT",
  "data":   {
    id:              String,
    bytesRead:       Long,
    sources:         Map[UUID, String],
    sourceConfigs:   Map[UUID, Map[String, Any]],
    sourcesStats:    Map[UUID, Map[Int, Map[String, Long]]],
    badRecordsTotal: Long,
    recordsSkipped:  Long,
    results:         Long,
    recordsScanned:  Long,
    duration:        Long,
    startedAt:       Long,
}

A possible payload can be:

{
  "type": "STATS",
  "data": {
    "id": "6a29ef99-3914-4640-b0dc-ec4a07c7ffc5",
    "bytesRead": 51972426,
    "sources": {
      "ad1afc73-3dec-41e7-b679-aa35c55e3328": "cc_payments"
    },
    "sourceConfigs": {
      "ad1afc73-3dec-41e7-b679-aa35c55e3328": {
        "live.aggs": true,
        "max.idle.time": 20000,
        "format.timestamp": true,
        "show.bad.records": true,
        "kafka.offset.timeout": 10000,
        "max.query.time": 3600000,
        "max.size": 209715200
      }
    },
    "sourcesStats": {
      "ad1afc73-3dec-41e7-b679-aa35c55e3328": {
        "0": {
          "begin": 0,
          "offsetBound": 541950,
          "bytesRead": 51972426,
          "recordsScanned": 541951,
          "end": 541950
        }
      }
    },
    "badRecordsTotal": 0,
    "recordsSkipped": 0,
    "results": 119,
    "recordsScanned": 541951,
    "duration": 18196,
    "startedAt": 1678901355694
  }
}

Metadata

The payload format is:

{
  "type": "METADATA",
  "data": {
    "fields": Array[String]
  }
}

End

The payload format is:

{
  "type": "END"
}

Bad Record

The payload format is:

{
  "type": "BADRECORD",
  "data": {
    "metadata": {
      "offset": Optional[Long],
      "partition": Optional[Long],
      "timestamp": Optional[Long],
      "table": String,
      "sourceId": String
    }
  }
}

Sentinel

The payload format is:

{
  "type": "SENTINEL",
  "data": {
    "event": String,
    "reason": {
      "type": String,
      "timeout":  Optional[Long],
      "source":   String,
      "sourceId": String,
      "amount":Long        
    }
  }
}

Record

Given the type RECORD the payloads contains the data returned to the client, and it is dependent on the SQL input. The payload format is:

{
  "type": "RECORD",
  "data": {
    "fields": <dynamic>,
    "value": <dynamic>,
    "metadata": <dynamic>,
    "rownum": Optional[Long]
  }
}

Value	Description
data.key	Returns the underlying Kafka message key value. Only applied when * projection is used. When a key projection is used (i.e. _key.MMSI), the value is returned as data.value.MMSI.
data.data	Will contain the output generated by the SQL projections. If * is used for the SQL projection, it will return the Kafka message value structure.
data.metadata	Returned when no aggregations are involved. It contains the Kafka message partition, offset, byte size information
data.rownum	Reserved optional long value.

Examples

For a topic which contains nested data for both key and value.

SELECT * FROM sea_vessel_position_reports

The payload format is:

{
  "type": "RECORD",
  "data": {
    "key": {
      "MMSI": 219005662
    },
    "value": {
      "Type": 1,
      "Repeat": 0,
      "MMSI": 219005662,
      "Speed": 0.1,
      "Accuracy": false,
      "Longitude": 12.570543333333333,
      "Latitude": 55.85040166666667,
      "location": "55.850402,12.570543",
      "Course": 177.9,
      "Heading": 511,
      "Second": 20,
      "RAIM": false,
      "Radio": 33577,
      "Status": 3,
      "Turn": -128.0,
      "Maneuver": 0,
      "Timestamp": 1491318144456507320
    },
    "metadata": {
      "offset": 71,
      "partition": 1,
      "timestamp": "2023-03-13T11:42:24.267Z",
      "__keysize": 10,
      "__valuesize": 79,
      "keySchemaId": 4,
      "valueSchemaId": 5
    },
    "rownum": 71
  }
}

If the Kafka message key is null the response would be:

{
  "type": "RECORD",
  "data": {
    "value": {
      "Type": 1,
      "Repeat": 0,
      "MMSI": 219005662,
      "Speed": 0.1,
      "Accuracy": false,
      "Longitude": 12.570543333333333,
      "Latitude": 55.85040166666667,
      "location": "55.850402,12.570543",
      "Course": 177.9,
      "Heading": 511,
      "Second": 20,
      "RAIM": false,
      "Radio": 33577,
      "Status": 3,
      "Turn": -128.0,
      "Maneuver": 0,
      "Timestamp": 1491318144456507320
    },
    "metadata": {
      "offset": 71,
      "partition": 1,
      "timestamp": "2023-03-13T11:42:24.267Z",
      "__keysize": 10,
      "__valuesize": 79,
      "keySchemaId": 4,
      "valueSchemaId": 5
    },
    "rownum": 71
  }
}

Projecting the key will not return the key attribute:

SELECT _key.MMSI FROM sea_vessel_position_reports

produces the following output:

{
  "type": "RECORD",
  "data": {
    "value": {
      "MMSI": 265527470
    },
    "metadata": {
      "offset": 86,
      "partition": 1,
      "timestamp": "2023-03-13T11:42:29.107Z",
      "__keysize": 10,
      "__valuesize": 79,
      "keySchemaId": 4,
      "valueSchemaId": 5
    },
    "rownum": 86
  }
}

Aggregating data will not return the key and metadata attributes:

SELECT count(*), currency 
FROM cc_payments
GROUP BY currency

{
  "type": "RECORD",
  "data": {
    "value": {
      "count": 20066,
      "currency": "NOR"
    },
    "rownum": 90
  },
  "rowId": "fc767952-97e5-46cf-868c-7cbfbcde21fb",
  "statementIndex": null
}