Add VirtualThreadQueryObservationConvention

In a virtual thread environment, thread names are always unique.
Tagging them as low-cardinality keys can lead to high-cardinality
issues in observability backends.
This change introduces `VirtualThreadQueryObservationConvention`, which
avoids tagging the thread name.

Fixes #149

Author: ttddyy

src/main/java/io/r2dbc/proxy/observation/VirtualThreadQueryObservationConvention.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed 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
+ *
+ *      https://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 io.r2dbc.proxy.observation;
+
+import io.micrometer.common.KeyValue;
+import io.micrometer.common.KeyValues;
+
+/**
+ * An extended {@link QueryObservationConvention} that excludes the thread name from low cardinality tags.
+ * This is particularly useful in environments using virtual threads, where thread names are always unique
+ * and no longer suitable for low cardinality tags.
+ *
+ * @author Tadaya Tsuyukubo
+ * @since 1.1.6
+ */
+public interface VirtualThreadQueryObservationConvention extends QueryObservationConvention {
+
+    @Override
+    default KeyValues getLowCardinalityKeyValues(QueryContext context) {
+        // does not include thread-name
+        return KeyValues.of(KeyValue.of(R2dbcObservationDocumentation.LowCardinalityKeys.CONNECTION, context.getConnectionName()));
+    }
+
+}

src/test/java/io/r2dbc/proxy/observation/VirtualThreadQueryObservationConventionTest.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed 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
+ *
+ *      https://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 io.r2dbc.proxy.observation;
+
+import io.micrometer.common.KeyValue;
+import io.micrometer.common.KeyValues;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Test for {@link VirtualThreadQueryObservationConvention}.
+ *
+ * @author Tadaya Tsuyukubo
+ */
+class VirtualThreadQueryObservationConventionTest {
+
+    VirtualThreadQueryObservationConvention convention = new VirtualThreadQueryObservationConvention() {
+
+    };
+
+    @Test
+    void keyValues() {
+        QueryContext context = new QueryContext();
+        context.setConnectionName("my-connection");
+        context.setThreadName("my-thread");
+
+        KeyValues keyValues = convention.getLowCardinalityKeyValues(context);
+
+        assertThat(keyValues).containsOnly(KeyValue.of(R2dbcObservationDocumentation.LowCardinalityKeys.CONNECTION.asString(), "my-connection"));
+    }
+
+}