Querying

Every query goes to one endpoint:

POST /api/query
Content-Type: application/json

The request body chooses one of two query styles:

Style	When to use	Body key
JSON DSL	A client program or a query builder	select, from, filters, …
SQL	An expert user or an ad-hoc analysis	sql

Both styles use the same output field. They also use the same support endpoints.

Support endpoints

Validate

Check that a query body is correct. Beacon parses it into a valid query. Beacon does not run it. This is a check of the structure. It does not check the column types:

POST /api/parse-query
Content-Type: application/json

{ "select": ["time", "temperature"], "limit": 1 }

Explain

Returns the query plan. Beacon does not run the query. Use this to debug and to tune performance:

POST /api/explain-query
Content-Type: application/json

{ "select": ["time", "temperature"], "limit": 1 }

Explain Analyze

Runs the query. It then returns the physical plan with the runtime metrics of each operator. The metrics give the rows, the bytes and the time of each node. This matches EXPLAIN ANALYZE in SQL. The endpoint runs the query. The same SQL rules as /api/query therefore apply. A sql body fails when BEACON_ENABLE_SQL=false:

POST /api/explain-analyze-query
Content-Type: application/json

{ "select": ["time", "temperature"], "limit": 1 }

Query metrics

Beacon returns a query ID in the x-beacon-query-id response header. Use the ID after the query to fetch the timing and the row count:

GET /api/query/metrics/{query_id}

Only the user that ran the query and the super-user get the metrics. Other users get 404.

Default response: Arrow IPC stream

Without an output field, /api/query returns an Apache Arrow IPC stream. The content type is application/vnd.apache.arrow.stream. This is the fastest format for a later process.

Client libraries:

• Python: PyArrow open_stream / RecordBatchStreamReader
• Rust: arrow-ipc StreamReader
• C++: RecordBatchStreamReader

Output formats

Add an output field to download one file. Beacon then does not stream Arrow IPC.

Simple formats

Set output.format to csv, parquet, netcdf or ipc. The alias of ipc is arrow.

POST /api/query
Content-Type: application/json

{
  "select": ["time", "temperature"],
  "output": { "format": "csv" }
}

GeoParquet

This format needs a longitude column and a latitude column:

POST /api/query
Content-Type: application/json

{
  "select": ["longitude", "latitude", "time", "temperature"],
  "output": {
    "format": {
      "geoparquet": {
        "longitude_column": "longitude",
        "latitude_column": "latitude"
      }
    }
  }
}

N-dimensional NetCDF

Builds a multi-dimensional NetCDF file from the result. The named columns become the dimension axes:

POST /api/query
Content-Type: application/json

{
  "select": ["time", "depth", "temperature"],
  "output": {
    "format": {
      "nd_netcdf": {
        "dimension_columns": ["time", "depth"]
      }
    }
  }
}

ODV (Ocean Data View)

Exports the result as an Ocean Data View collection. Beacon returns a ZIP archive. ODV needs the columns of the station coordinates. It also needs to know the data columns and the metadata columns. An options object gives this:

POST /api/query
Content-Type: application/json

{
  "select": ["cruise", "longitude", "latitude", "depth", "time", "temperature"],
  "output": {
    "format": {
      "odv": {
        "longitude_column": { "column_name": "longitude" },
        "latitude_column": { "column_name": "latitude" },
        "depth_column": { "column_name": "depth" },
        "time_column": { "column_name": "time" },
        "key_column": "cruise",
        "qf_schema": "SEADATANET",
        "data_columns": [{ "column_name": "temperature" }],
        "meta_columns": []
      }
    }
  }
}

Each entry in *_column, data_columns and meta_columns names a result column. An entry can also hold ODV attributes, such as the units and the quality flag column. key_column groups the rows into ODV stations. qf_schema selects the quality flag scheme. You can configure the compression and the archive. The response is always a ZIP file.

Data sources

Most queries use the name of a registered table:

{ "from": "default", "select": ["time"] }

Both styles also query files directly, without a registered table. See the JSON DSL from reference and the SQL table functions.