Bucket gql.loaderBatchSize tag to limit metric cardinality

graphql-dgs-spring-boot-micrometer/src/main/kotlin/com/netflix/graphql/dgs/metrics/micrometer/dataloader/BatchLoaderWithContextInterceptor.kt

@@ -46,7 +46,7 @@ internal class BatchLoaderWithContextInterceptor(
                             .tags(
                                 listOf(
                                     Tag.of(GqlTag.LOADER_NAME.key, name),
-                                    Tag.of(GqlTag.LOADER_BATCH_SIZE.key, resultSize.toString()),
+                                    Tag.of(GqlTag.LOADER_BATCH_SIZE.key, bucketBatchSize(resultSize).toString()),
                                 ),
                             ).register(registry),
                     )
@@ -65,5 +65,21 @@ internal class BatchLoaderWithContextInterceptor(
     companion object {
         private val ID = GqlMetric.DATA_LOADER.key
         private val logger = LoggerFactory.getLogger(BatchLoaderWithContextInterceptor::class.java)
+
+        private val BATCH_SIZE_BUCKETS = listOf(5, 10, 25, 50, 100, 200, 500, 1000, 2000, 5000, 10000)
+
+        /**
+         * Buckets the given batch size into a predefined range to limit metric cardinality.
+         * Uses the same bucketing approach as query complexity in [DgsGraphQLMetricsInstrumentation].
+         * Returns the smallest bucket that the size falls below, or [Int.MAX_VALUE] if it exceeds all buckets.
+         */
+        internal fun bucketBatchSize(size: Int): Int {
+            for (bucket in BATCH_SIZE_BUCKETS) {
+                if (size < bucket) {
+                    return bucket
+                }
+            }
+            return Int.MAX_VALUE
+        }
     }
 }

graphql-dgs-spring-boot-micrometer/src/test/kotlin/com/netflix/graphql/dgs/metrics/micrometer/dataloader/BatchLoaderWithContextInterceptorTest.kt

@@ -0,0 +1,100 @@
+/*
+ * Copyright 2025 Netflix, Inc.
+ *
+ * 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
+ *
+ *    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 com.netflix.graphql.dgs.metrics.micrometer.dataloader
+
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+
+internal class BatchLoaderWithContextInterceptorTest {
+    @Test
+    fun `batch size 0 is bucketed to 5`() {
+        assertThat(BatchLoaderWithContextInterceptor.bucketBatchSize(0)).isEqualTo(5)
+    }
+
+    @Test
+    fun `batch size 1 is bucketed to 5`() {
+        assertThat(BatchLoaderWithContextInterceptor.bucketBatchSize(1)).isEqualTo(5)
+    }
+
+    @Test
+    fun `batch size 4 is bucketed to 5`() {
+        assertThat(BatchLoaderWithContextInterceptor.bucketBatchSize(4)).isEqualTo(5)
+    }
+
+    @Test
+    fun `batch size 5 is bucketed to 10`() {
+        assertThat(BatchLoaderWithContextInterceptor.bucketBatchSize(5)).isEqualTo(10)
+    }
+
+    @Test
+    fun `batch size 9 is bucketed to 10`() {
+        assertThat(BatchLoaderWithContextInterceptor.bucketBatchSize(9)).isEqualTo(10)
+    }
+
+    @Test
+    fun `batch size 10 is bucketed to 25`() {
+        assertThat(BatchLoaderWithContextInterceptor.bucketBatchSize(10)).isEqualTo(25)
+    }
+
+    @Test
+    fun `batch size 24 is bucketed to 25`() {
+        assertThat(BatchLoaderWithContextInterceptor.bucketBatchSize(24)).isEqualTo(25)
+    }
+
+    @Test
+    fun `batch size 25 is bucketed to 50`() {
+        assertThat(BatchLoaderWithContextInterceptor.bucketBatchSize(25)).isEqualTo(50)
+    }
+
+    @Test
+    fun `batch size 99 is bucketed to 100`() {
+        assertThat(BatchLoaderWithContextInterceptor.bucketBatchSize(99)).isEqualTo(100)
+    }
+
+    @Test
+    fun `batch size 100 is bucketed to 200`() {
+        assertThat(BatchLoaderWithContextInterceptor.bucketBatchSize(100)).isEqualTo(200)
+    }
+
+    @Test
+    fun `batch size 500 is bucketed to 1000`() {
+        assertThat(BatchLoaderWithContextInterceptor.bucketBatchSize(500)).isEqualTo(1000)
+    }
+
+    @Test
+    fun `batch size 9999 is bucketed to 10000`() {
+        assertThat(BatchLoaderWithContextInterceptor.bucketBatchSize(9999)).isEqualTo(10000)
+    }
+
+    @Test
+    fun `batch size 10000 exceeds all buckets`() {
+        assertThat(BatchLoaderWithContextInterceptor.bucketBatchSize(10000)).isEqualTo(Int.MAX_VALUE)
+    }
+
+    @Test
+    fun `batch size 50000 exceeds all buckets`() {
+        assertThat(BatchLoaderWithContextInterceptor.bucketBatchSize(50000)).isEqualTo(Int.MAX_VALUE)
+    }
+
+    @Test
+    fun `all bucket boundaries produce at most 12 distinct values`() {
+        val distinctValues =
+            (0..50000).map { BatchLoaderWithContextInterceptor.bucketBatchSize(it) }.distinct().sorted()
+        assertThat(distinctValues).hasSize(12)
+        assertThat(distinctValues).containsExactly(5, 10, 25, 50, 100, 200, 500, 1000, 2000, 5000, 10000, Int.MAX_VALUE)
+    }
+}