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docs/source/cpp/opentelemetry.rst

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.. _cpp_opentelemetry:

============= OpenTelemetry

Portions of Arrow C++ are instrumented with the OpenTelemetry <https://opentelemetry.io/>_ C++ SDK which makes it possible to generate detailed tracing information which can be analyzed in other tools.

Creating a Build with OpenTelemetry Tracing Enabled

OpenTelemetry tracing is not turned on by default so you must first create a custom build of Arrow C++ with tracing turned on. See :ref:Building Arrow C++ <building-arrow-cpp> for general instructions on creating a custom build.

To enable tracing, specify ARROW_WITH_OPENTELEMETRY=ON when generating your build. You may also want to specify CMAKE_BUILD_TYPE=RelWithDebInfo in order to get representative timings while retaining debug information.

Exporting Tracing Information

By default, no tracing information is exported until a tracing backend has been specified. This is typically done by the executable using Arrow by installing a TracerProvider through the OpenTelemetry SDK API. Please refer to the OpenTelemetry SDK API C++ documentation <https://opentelemetry-cpp.readthedocs.io/en/latest/sdk/sdk.html>_.

In the rare cases you want Arrow to control the global resources of the OpenTelemetry SDK, a tracing backend can be specified through the :envvar:ARROW_TRACING_BACKEND environment variable. This overrides any TracerProvider previously set.

Possible values for :envvar:ARROW_TRACING_BACKEND are:

  • ostream: emit textual log messages to stdout
  • otlp_http: emit OTLP JSON encoded traces to a HTTP server (by default, the endpoint URL is "http://localhost:4318/v1/traces")
  • arrow_otlp_stdout: emit JSON traces to stdout
  • arrow_otlp_stderr: emit JSON traces to stderr

For example, to enable exporting JSON traces to stdout, set::

export ARROW_TRACING_BACKEND=arrow_otlp_stdout

At this point, running the program you've linked to your custom build of Arrow C++ should produce JSON traces on stdout.

Visualizing Traces with Jaeger UI

Analyzing trace information exported to stdout/stderr may involve writing custom processing scripts. As an alternative -- or even a complement -- to this process, the "all-in-one" Jaeger <https://jaegertracing.io>_ Docker <https://www.docker.com/>_ image is a relatively straightforward way of visualizing trace data and is suitable for local development and testing.

Note: This assumes you have Docker <https://www.docker.com/>_ installed.

First, change your tracing backend to otlp_http::

export ARROW_TRACING_BACKEND=otlp_http

Then start the Jaeger all-in-one container::

docker run
-e COLLECTOR_OTLP_ENABLED=true
-p 16686:16686
-p 4317:4317
-p 4318:4318
jaegertracing/all-in-one:1.35

Now you should be able to run your program and view any traces in a web browser at http://localhost:16686. Note that unlike with other methods of exporting traces, no output will be made to stdout/stderr. However, if you tail your Docker container logs, you should see output when traces are received by the all-in-one container.