Telemetry

AshClickhouse emits telemetry around every query executed against ClickHouse via AshClickhouse.Telemetry.

Events

All events are prefixed with [:ash_clickhouse, :query]:

These mirror the structure used by other Ash data layers, so existing Ash telemetry tooling and dashboards can consume them.

Metadata

Each event carries the following metadata:

• :resource — the Ash resource (or nil)
• :query — the SQL query string
• :event — the event atom (e.g. :run_query)
• :status — :ok or :error on the :stop event. This distinguishes a successful query from one that returned {:error, _}. (Errors that are raised by the ClickHouse client are reported via the :exception event instead, so they do not appear as :stop with status: :error.)

The :stop and :exception events also include the result/error in the standard :telemetry.span/3 measurement and result tuples.

Attaching a handler

:telemetry.attach(
  "ash-clickhouse-logger",
  [:ash_clickhouse, :query, :stop],
  fn _event, _measure, meta, _config ->
    Logger.debug("ClickHouse query on #{inspect(meta.resource)}: #{meta.query}")
  end,
  nil
)

How it works

AshClickhouse.Telemetry.span/4 wraps the query function with :telemetry.span/3. Exceptions raised inside the function are caught by the span, the :exception event is emitted, and the error is reraised so the data layer can translate it into an AshClickhouse.Error.ClickhouseError.