Emitting trace events in Java

You can use the com.snowflake.telemetry.Telemetry class in the Snowflake Telemetry API (https://javadoc.io/doc/com.snowflake/telemetry/latest/index.html) library to emit trace events from a function or procedure handler written in Java. The Telemetry class is included with Snowflake.

Note

Using the Snowflake Telemetry Library adds other libraries to your function or procedure’s execution environment. For more information, see Snowflake telemetry package dependencies.

For information on including the Telemetry library when packaging your code with Maven, see Setting up your Java and Scala environment to use the Telemetry class.

You can access stored trace event data by executing a SELECT command on the event table. For more information, see Viewing trace data.

Note

For guidelines to keep in mind when adding trace events, see General guidelines for adding trace events.

For general information about setting up logging and retrieving messages in Snowflake, see Logging messages from functions and procedures.

Before logging from code, you must:

Adding support for the telemetry API

To use Telemetry methods, you must make the open source Snowflake telemetry package (https://central.sonatype.com/artifact/com.snowflake/telemetry) available to your handler code.

  • In the PACKAGES clause in your CREATE PROCEDURE or CREATE FUNCTION statement, include the com.snowflake:telemetry package. The PACKAGES clause makes the included Snowflake Telemetry API available to your code.

    Code in the following example uses the PACKAGES clause to reference the Telemetry library as well as the Snowpark library (which is required for stored procedures written in Java – for more information, see Writing Java handlers for stored procedures created with SQL).

    CREATE OR REPLACE PROCEDURE myproc(...)
  RETURNS ...
  LANGUAGE JAVA
  ...
  PACKAGES = ('com.snowflake:snowpark:latest', 'com.snowflake:telemetry:latest')
  ...

  • Import the com.snowflake.telemetry package in your Java handler code.

    import com.snowflake.telemetry.Telemetry;

Adding trace events

You can add trace events by calling the Telemetry.addEvent method, passing a name for the event. You can also optionally associate attributes – key-value pairs – with an event.

The addEvent method has the following signatures:

public static void addEvent(String name)
public static void addEvent(String name, Attributes attributes)

Code in the following example adds an event called testEvent, associating with the event two attributes: key and result.

// Adding an event without attributes.
Telemetry.addEvent("testEvent");

// Adding an event with attributes.
Attributes eventAttributes = Attributes.of(
  AttributeKey.stringKey("key"), "run",
  AttributeKey.longKey("result"), Long.valueOf(123));
Telemetry.addEvent("testEventWithAttributes", eventAttributes);

Adding these events results in two rows in the event table, each with a different value in the RECORD column:

{
  "name": "testEvent"
}
{
  "name": "testEventWithAttributes"
}

The testEventWithAttributes event row includes the following attributes in the row’s RECORD_ATTRIBUTES column:

{
  "key": "run",
  "result": 123
}

Adding span attributes

You can set attributes – key-value pairs – associated with spans by calling the Telemetry.setSpanAttribute method.

The setSpanAttribute method has the following signatures:

public static void setSpanAttribute(String key, boolean value)
public static void setSpanAttribute(String key, long value)
public static void setSpanAttribute(String key, double value)
public static void setSpanAttribute(String key, String value)

For details on spans, see How Snowflake represents trace events.

Code in the following example creates four attributes and sets their values:

// Setting span attributes.
Telemetry.setSpanAttribute("example.boolean", true);
Telemetry.setSpanAttribute("example.long", 2L);
Telemetry.setSpanAttribute("example.double", 2.5);
Telemetry.setSpanAttribute("example.string", "testAttribute");

Setting these attributes results in the following in the event table’s RECORD_ATTRIBUTES column:

{
  "example.boolean": true,
  "example.long": 2,
  "example.double": 2.5,
  "example.string": "testAttribute"
}

Adding custom spans

You can add custom spans that are separate from the default span created by Snowflake. For details on custom spans, see Adding custom spans to a trace.

Code in the following example uses the OpenTelemetry API (https://javadoc.io/doc/io.opentelemetry/opentelemetry-api/latest/index.html) and OpenTelemetry context propagation API (https://www.javadoc.io/doc/io.opentelemetry/opentelemetry-context-prop/latest/index.html) to create a new my.span span. It then adds an event with attributes to the new span. Finally, the code ends the span to have the span’s event data captured in the event table. If the code doesn’t call the Span.end method, data is not captured in the event table.

CREATE OR REPLACE FUNCTION customSpansJavaExample() RETURNS STRING
  LANGUAGE JAVA
  PACKAGES = ('com.snowflake:telemetry:latest')
  HANDLER = 'MyJavaClass.run'
  as
  $$
  import com.snowflake.telemetry.Telemetry;
  import io.opentelemetry.api.common.AttributeKey;
  import io.opentelemetry.api.common.Attributes;
  import io.opentelemetry.api.GlobalOpenTelemetry;
  import io.opentelemetry.api.trace.Tracer;
  import io.opentelemetry.api.trace.Span;
  import io.opentelemetry.context.Scope;

  class MyJavaClass {
    public static String run() {
      Tracer tracer = GlobalOpenTelemetry.getTracerProvider().get("my.tracer");
      Span span = tracer.spanBuilder("my.span").startSpan();
      try (Scope scope = span.makeCurrent()) {
        // Do processing, adding events that will be captured in a my.span.

        // Add an event with attributes.
        Attributes eventAttributes = Attributes.of(
          AttributeKey.stringKey("key"), "run",
          AttributeKey.longKey("result"), Long.valueOf(123));

        span.addEvent("testEventWithAttributes", eventAttributes);
        span.setAttribute("testAttribute", "value");

      } finally {
        span.end();
      }
      return "success";
    }
  }
  $$;

Java examples

Stored procedure example

CREATE OR REPLACE PROCEDURE do_tracing()
  RETURNS STRING
  LANGUAGE JAVA
  RUNTIME_VERSION = '11'
  PACKAGES=('com.snowflake:snowpark:latest', 'com.snowflake:telemetry:latest')
  HANDLER = 'ProcedureHandler.run'
  AS
  $$
  import com.snowflake.snowpark_java.Session;
  import com.snowflake.telemetry.Telemetry;
  import io.opentelemetry.api.common.AttributeKey;
  import io.opentelemetry.api.common.Attributes;

  public class ProcedureHandler {

    public String run(Session session) {

      // Set span attribute.
      Telemetry.setSpanAttribute("example.proc.do_tracing", "begin");

      // Add an event without attributes.
      Telemetry.addEvent("run_method_start");

      // Add an event with attributes.
      Attributes eventAttributes = Attributes.of(
        AttributeKey.stringKey("example.method.name"), "run",
        AttributeKey.longKey("example.long"), Long.valueOf(123));
      Telemetry.addEvent("event_with_attributes", eventAttributes);

      // Set span attribute.
      Telemetry.setSpanAttribute("example.proc.do_tracing", "complete");

      return "SUCCESS";
    }
  }
  $$;

UDF example

CREATE OR REPLACE FUNCTION add_two_numbers(A FLOAT, B FLOAT) RETURNS FLOAT
  LANGUAGE JAVA
  PACKAGES=('com.snowflake:telemetry:latest')
  HANDLER = 'ScalarFunctionHandler.run'
  AS
  $$
  import com.snowflake.telemetry.Telemetry;
  import io.opentelemetry.api.common.AttributeKey;
  import io.opentelemetry.api.common.Attributes;
  import io.opentelemetry.api.common.AttributesBuilder;

  class ScalarFunctionHandler {

    public static Double run(Double d0, Double d1) {

      // Set span attribute.
      Telemetry.setSpanAttribute("example.func.add_two_numbers", "begin");

      // Add an event without attributes.
      Telemetry.addEvent("run_method_start");

      // Add an event with attributes.
      Attributes eventAttributes = Attributes.of(
        AttributeKey.stringKey("example.method.name"), "run",
        AttributeKey.longKey("example.long"), Long.valueOf(123));
      Telemetry.addEvent("event_with_attributes", eventAttributes);

      Double response = d0 == null || d1 == null ? null : (d0 + d1);

      // Set span attribute.
      Telemetry.setSpanAttribute("example.func.add_two_numbers.response", response);
      Telemetry.setSpanAttribute("example.func.add_two_numbers", "complete");

      return response;
    }
  }
  $$;

UDTF example

CREATE OR REPLACE FUNCTION digits_of_number(x int)
  RETURNS TABLE(result INT)
  LANGUAGE JAVA
  PACKAGES = ('com.snowflake:telemetry:latest')
  HANDLER = 'TableFunctionHandler'
  AS
  $$
  import com.snowflake.telemetry.Telemetry;
  import io.opentelemetry.api.common.AttributeKey;
  import io.opentelemetry.api.common.Attributes;
  import io.opentelemetry.api.common.AttributesBuilder;
  import java.util.stream.Stream;

  public class TableFunctionHandler {

    public TableFunctionHandler() {
      // Set span attribute.
      Telemetry.setSpanAttribute("example.func.digits_of_number", "begin");
    }

    static class OutputRow {
      public int result;

      public OutputRow(int result) {
        this.result = result;
      }
    }

    public static Class getOutputClass() {
      return OutputRow.class;
    }

    public Stream<OutputRow> process(int input) {

      // Add an event with attributes.
      Attributes eventAttributes = Attributes.of(
        AttributeKey.longKey("example.received.value"), Long.valueOf(input));
      Telemetry.addEvent("digits_of_number", eventAttributes);

      Stream.Builder<OutputRow> stream = Stream.builder();
      while (input > 0) {

        stream.add(new OutputRow(input %10));
        input /= 10;
      }

      // Set span attribute.
      Telemetry.setSpanAttribute("example.func.digits_of_number", "complete");

      return stream.build();
    }
  }
  $$;