nastra commented on code in PR #16250:
URL: https://github.com/apache/iceberg/pull/16250#discussion_r3529931146


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core/src/main/java/org/apache/iceberg/metrics/OtelMetricsReporter.java:
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@@ -0,0 +1,651 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.iceberg.metrics;
+
+import io.opentelemetry.api.GlobalOpenTelemetry;
+import io.opentelemetry.api.OpenTelemetry;
+import io.opentelemetry.api.common.AttributeKey;
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.api.common.AttributesBuilder;
+import io.opentelemetry.api.metrics.DoubleHistogram;
+import io.opentelemetry.api.metrics.LongCounter;
+import io.opentelemetry.api.metrics.Meter;
+import java.util.Arrays;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+import org.apache.iceberg.relocated.com.google.common.collect.ImmutableMap;
+import org.apache.iceberg.relocated.com.google.common.collect.ImmutableSet;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * A {@link MetricsReporter} that exports Iceberg {@link ScanReport} and 
{@link CommitReport} via
+ * OpenTelemetry.
+ *
+ * <p>The reporter does not own the OpenTelemetry SDK. It obtains the {@link 
OpenTelemetry} instance
+ * from {@link GlobalOpenTelemetry}, which the host application (Spark, Flink, 
Trino, ...) is
+ * expected to register — typically via {@code
+ * OpenTelemetrySdk.builder()...buildAndRegisterGlobal()} or via the 
OpenTelemetry Java agent. If no
+ * SDK has been registered, OpenTelemetry returns a no-op implementation and 
metric calls are
+ * silently dropped, matching the standard OpenTelemetry API contract.
+ *
+ * <p>Endpoint, exporter, headers, resource attributes, and exporter intervals 
are configured by the
+ * host application or via the standard OpenTelemetry environment variables 
(e.g. {@code
+ * OTEL_EXPORTER_OTLP_ENDPOINT}, {@code OTEL_SERVICE_NAME}, {@code 
OTEL_EXPORTER_OTLP_HEADERS}).
+ *
+ * <p>Configure as the Iceberg metrics reporter via catalog properties:
+ *
+ * <pre>{@code
+ * metrics-reporter-impl=org.apache.iceberg.metrics.OtelMetricsReporter
+ * }</pre>
+ *
+ * <h2>Cardinality</h2>
+ *
+ * By default every emitted metric carries the following attribute set:
+ *
+ * <ul>
+ *   <li>Scan metrics: {@code iceberg.table.name}
+ *   <li>Commit metrics: {@code iceberg.table.name}, {@code iceberg.operation}
+ * </ul>
+ *
+ * <p>The set of attributes is configurable via the {@code 
iceberg.otel.metrics.attributes} catalog
+ * property, which takes a comma-separated allowlist of attribute short names. 
Recognized names are
+ * {@code table-name}, {@code schema-id}, and {@code operation}; any attribute 
whose short name is
+ * not listed is omitted from emitted metric points.
+ *
+ * <p>For example, to additionally include {@code iceberg.schema.id} (useful 
for correlating scan
+ * performance with schema evolution):
+ *
+ * <pre>{@code
+ * iceberg.otel.metrics.attributes=table-name,schema-id,operation
+ * }</pre>
+ *
+ * <p>Or to exclude {@code iceberg.table.name} entirely in deployments with a 
very large number of
+ * tables:
+ *
+ * <pre>{@code
+ * iceberg.otel.metrics.attributes=operation
+ * }</pre>
+ *
+ * <p>Or to emit metrics with no attributes at all (single aggregate time 
series per metric), use
+ * {@code none} or an empty string:
+ *
+ * <pre>{@code
+ * iceberg.otel.metrics.attributes=none
+ * }</pre>
+ *
+ * <p>When the property is not set, the default attribute set above is used.
+ *
+ * <p>The snapshot id is deliberately <b>not</b> attached as a metric 
attribute. Snapshot ids are
+ * monotonically increasing and unique per commit, so including them would 
create a new time series
+ * for every commit and risk unbounded cardinality in any time-series backend 
(Prometheus,
+ * CloudWatch, Datadog, etc.).
+ */
+public class OtelMetricsReporter implements MetricsReporter {
+  private static final Logger LOG = 
LoggerFactory.getLogger(OtelMetricsReporter.class);
+  private static final String INSTRUMENTATION_NAME = "org.apache.iceberg";
+
+  static final String ATTRIBUTES_PROPERTY = "iceberg.otel.metrics.attributes";
+  static final String ATTR_NAME_TABLE_NAME = "table-name";
+  static final String ATTR_NAME_SCHEMA_ID = "schema-id";
+  static final String ATTR_NAME_OPERATION = "operation";
+  static final String ATTR_VALUE_NONE = "none";
+  private static final Set<String> KNOWN_ATTRIBUTE_NAMES =
+      ImmutableSet.of(ATTR_NAME_TABLE_NAME, ATTR_NAME_SCHEMA_ID, 
ATTR_NAME_OPERATION);
+
+  static final AttributeKey<String> ATTR_TABLE_NAME = 
AttributeKey.stringKey("iceberg.table.name");
+  static final AttributeKey<Long> ATTR_SCHEMA_ID = 
AttributeKey.longKey("iceberg.schema.id");
+  static final AttributeKey<String> ATTR_OPERATION = 
AttributeKey.stringKey("iceberg.operation");
+
+  private Meter meter;
+  private boolean includeTableName = true;
+  private boolean includeSchemaId = false;
+  private boolean includeOperation = true;
+
+  // Scan metrics instruments
+  private DoubleHistogram scanPlanningDuration;

Review Comment:
   it might be worth having a small wrapper class so that you don't have to 
prefix all of the metrics with either scan or commit. That wrapper could have a 
static method where it converts from `ScanMetricsResult` to that wrapper with 
all the counters initialized/converted.
   The same would apply for the commit metrics



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