Add metrics around the file extensions we request when populating the cache

This adds the file extentions for the blobs we request when populating the
cache.
The possible values for lucene extensions are around 50 and we use a special
"other" category for everything else, as a fallback.

Author: andreidan

x-pack/plugin/blob-cache/src/main/java/org/elasticsearch/blobcache/BlobCacheMetrics.java

@@ -9,6 +9,7 @@
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
+import org.elasticsearch.index.store.LuceneFilesExtensions;
 import org.elasticsearch.telemetry.TelemetryProvider;
 import org.elasticsearch.telemetry.metric.DoubleHistogram;
 import org.elasticsearch.telemetry.metric.LongCounter;
@@ -24,8 +25,8 @@ public class BlobCacheMetrics {
     private static final double BYTES_PER_NANOSECONDS_TO_MEBIBYTES_PER_SECOND = 1e9D / (1 << 20);
     public static final String CACHE_POPULATION_REASON_ATTRIBUTE_KEY = "reason";
     public static final String CACHE_POPULATION_SOURCE_ATTRIBUTE_KEY = "source";
-    public static final String SHARD_ID_ATTRIBUTE_KEY = "shard_id";
-    public static final String INDEX_ATTRIBUTE_KEY = "index_name";
+    public static final String LUCENE_FILE_EXTENSION_ATTRIBUTE_KEY = "file_extension";
+    public static final String NON_LUCENE_EXTENSION_TO_RECORD = "other";
 
     private final LongCounter cacheMissCounter;
     private final LongCounter evictedCountNonZeroFrequency;
@@ -113,22 +114,28 @@ public LongHistogram getCacheMissLoadTimes() {
     /**
      * Record the various cache population metrics after a chunk is copied to the cache
      *
+     * @param blobName The file that was requested and triggered the cache population.
      * @param bytesCopied The number of bytes copied
      * @param copyTimeNanos The time taken to copy the bytes in nanoseconds
      * @param cachePopulationReason The reason for the cache being populated
      * @param cachePopulationSource The source from which the data is being loaded
      */
     public void recordCachePopulationMetrics(
+        String blobName,
         int bytesCopied,
         long copyTimeNanos,
         CachePopulationReason cachePopulationReason,
         CachePopulationSource cachePopulationSource
     ) {
+        LuceneFilesExtensions luceneFilesExtensions = LuceneFilesExtensions.fromFile(blobName);
+        String blobFileExtension = luceneFilesExtensions != null ? luceneFilesExtensions.getExtension() : NON_LUCENE_EXTENSION_TO_RECORD;
         Map<String, Object> metricAttributes = Map.of(
             CACHE_POPULATION_REASON_ATTRIBUTE_KEY,
             cachePopulationReason.name(),
             CACHE_POPULATION_SOURCE_ATTRIBUTE_KEY,
-            cachePopulationSource.name()
+            cachePopulationSource.name(),
+            LUCENE_FILE_EXTENSION_ATTRIBUTE_KEY,
+            blobFileExtension
         );
         assert bytesCopied > 0 : "We shouldn't be recording zero-sized copies";
         cachePopulationBytes.incrementBy(bytesCopied, metricAttributes);

x-pack/plugin/blob-cache/src/test/java/org/elasticsearch/blobcache/BlobCacheMetricsTests.java

@@ -8,14 +8,18 @@
 package org.elasticsearch.blobcache;
 
 import org.elasticsearch.common.unit.ByteSizeValue;
+import org.elasticsearch.index.store.LuceneFilesExtensions;
 import org.elasticsearch.telemetry.InstrumentType;
 import org.elasticsearch.telemetry.Measurement;
 import org.elasticsearch.telemetry.RecordingMeterRegistry;
 import org.elasticsearch.test.ESTestCase;
 import org.junit.Before;
 
+import java.util.Arrays;
 import java.util.concurrent.TimeUnit;
 
+import static org.hamcrest.Matchers.is;
+
 public class BlobCacheMetricsTests extends ESTestCase {
 
     private RecordingMeterRegistry recordingMeterRegistry;
@@ -32,7 +36,10 @@ public void testRecordCachePopulationMetricsRecordsThroughput() {
         int secondsTaken = randomIntBetween(1, 5);
         BlobCacheMetrics.CachePopulationReason cachePopulationReason = randomFrom(BlobCacheMetrics.CachePopulationReason.values());
         CachePopulationSource cachePopulationSource = randomFrom(CachePopulationSource.values());
+        String fileExtension = randomFrom(Arrays.stream(LuceneFilesExtensions.values()).map(LuceneFilesExtensions::getExtension).toList());
+        String luceneBlobFile = randomAlphanumericOfLength(15) + "." + fileExtension;
         metrics.recordCachePopulationMetrics(
+            luceneBlobFile,
             Math.toIntExact(ByteSizeValue.ofMb(mebiBytesSent).getBytes()),
             TimeUnit.SECONDS.toNanos(secondsTaken),
             cachePopulationReason,
@@ -44,29 +51,31 @@ public void testRecordCachePopulationMetricsRecordsThroughput() {
             .getMeasurements(InstrumentType.DOUBLE_HISTOGRAM, "es.blob_cache.population.throughput.histogram")
             .get(0);
         assertEquals(throughputMeasurement.getDouble(), (double) mebiBytesSent / secondsTaken, 0.0);
-        assertExpectedAttributesPresent(throughputMeasurement, cachePopulationReason, cachePopulationSource);
+        assertExpectedAttributesPresent(throughputMeasurement, cachePopulationReason, cachePopulationSource, fileExtension);
 
         // bytes counter
         Measurement totalBytesMeasurement = recordingMeterRegistry.getRecorder()
             .getMeasurements(InstrumentType.LONG_COUNTER, "es.blob_cache.population.bytes.total")
             .get(0);
         assertEquals(totalBytesMeasurement.getLong(), ByteSizeValue.ofMb(mebiBytesSent).getBytes());
-        assertExpectedAttributesPresent(totalBytesMeasurement, cachePopulationReason, cachePopulationSource);
+        assertExpectedAttributesPresent(totalBytesMeasurement, cachePopulationReason, cachePopulationSource, fileExtension);
 
         // time counter
         Measurement totalTimeMeasurement = recordingMeterRegistry.getRecorder()
             .getMeasurements(InstrumentType.LONG_COUNTER, "es.blob_cache.population.time.total")
             .get(0);
         assertEquals(totalTimeMeasurement.getLong(), TimeUnit.SECONDS.toMillis(secondsTaken));
-        assertExpectedAttributesPresent(totalTimeMeasurement, cachePopulationReason, cachePopulationSource);
+        assertExpectedAttributesPresent(totalTimeMeasurement, cachePopulationReason, cachePopulationSource, fileExtension);
     }
 
     private static void assertExpectedAttributesPresent(
         Measurement measurement,
         BlobCacheMetrics.CachePopulationReason cachePopulationReason,
-        CachePopulationSource cachePopulationSource
+        CachePopulationSource cachePopulationSource,
+        String fileExtension
     ) {
-        assertEquals(measurement.attributes().get(BlobCacheMetrics.CACHE_POPULATION_REASON_ATTRIBUTE_KEY), cachePopulationReason.name());
-        assertEquals(measurement.attributes().get(BlobCacheMetrics.CACHE_POPULATION_SOURCE_ATTRIBUTE_KEY), cachePopulationSource.name());
+        assertThat(measurement.attributes().get(BlobCacheMetrics.CACHE_POPULATION_REASON_ATTRIBUTE_KEY), is(cachePopulationReason.name()));
+        assertThat(measurement.attributes().get(BlobCacheMetrics.CACHE_POPULATION_SOURCE_ATTRIBUTE_KEY), is(cachePopulationSource.name()));
+        assertThat(measurement.attributes().get(BlobCacheMetrics.LUCENE_FILE_EXTENSION_ATTRIBUTE_KEY), is(fileExtension));
     }
 }