Keep writeCount as is and introduce a miss count.

Author: henningandersen

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

@@ -40,7 +40,7 @@ public class BlobCacheMetrics {
     private final LongCounter cachePopulationBytes;
     private final LongCounter cachePopulationTime;
 
-    private final LongAdder writeCount = new LongAdder();
+    private final LongAdder missCount = new LongAdder();
     private final LongAdder readCount = new LongAdder();
 
     public enum CachePopulationReason {
@@ -114,7 +114,7 @@ public BlobCacheMetrics(MeterRegistry meterRegistry) {
             "es.blob_cache.miss.total",
             "The number of cache misses (warming not included)",
             "count",
-            () -> new LongWithAttributes(writeCount.longValue())
+            () -> new LongWithAttributes(missCount.longValue())
         );
         // adding this helps search for high or low miss ratio. It will be since boot of the node though. More advanced queries can use
         // deltas of the totals to see miss ratio over time.
@@ -123,7 +123,7 @@ public BlobCacheMetrics(MeterRegistry meterRegistry) {
             "The fraction of cache reads that missed data (warming not included)",
             "fraction",
             // read misses before reads on purpose
-            () -> new DoubleWithAttributes(Math.min((double) writeCount.longValue() / Math.max(readCount.longValue(), 1L), 1.0d))
+            () -> new DoubleWithAttributes(Math.min((double) missCount.longValue() / Math.max(readCount.longValue(), 1L), 1.0d))
         );
     }
 
@@ -205,17 +205,8 @@ public void recordRead() {
         readCount.increment();
     }
 
-    public void recordWrite() {
-        writeCount.increment();
-    }
-
-    public void recordWrites(long count) {
-        assert count > 0;
-        writeCount.add(count);
-    }
-
-    public long writeCount() {
-        return writeCount.sum();
+    public void recordMiss() {
+        missCount.increment();
     }
 
     public long readCount() {

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

@@ -325,6 +325,7 @@ private CacheEntry(T chunk) {
 
     private final ConcurrentHashMap<SharedBytes.IO, CacheFileRegion<KeyType>> regionOwners; // to assert exclusive access of regions
 
+    private final LongAdder writeCount = new LongAdder();
     private final LongAdder writeBytes = new LongAdder();
 
     private final LongAdder readBytes = new LongAdder();
@@ -737,7 +738,7 @@ public Stats getStats() {
             cacheSize,
             regionSize,
             evictCount.sum(),
-            blobCacheMetrics.writeCount(),
+            writeCount.sum(),
             writeBytes.sum(),
             blobCacheMetrics.readCount(),
             readBytes.sum()
@@ -1170,6 +1171,7 @@ private Runnable fillGapRunnable(
                     l.<Void>map(unused -> {
                         assert blobCacheService.regionOwners.get(ioRef) == CacheFileRegion.this;
                         assert CacheFileRegion.this.hasReferences() : CacheFileRegion.this;
+                        blobCacheService.writeCount.increment();
                         gap.onCompletion();
                         return null;
                     }).delegateResponse((delegate, e) -> failGapAndListener(gap, delegate, e))
@@ -1242,7 +1244,7 @@ public boolean tryRead(ByteBuffer buf, long offset) throws IOException {
             lastAccessedRegion = res ? fileRegion : null;
             if (res && incrementReads) {
                 blobCacheMetrics.recordRead();
-                readBytes.add(end - offset);
+                // todo: should we add to readBytes? readBytes.add(end - offset);
             }
             return res;
         }
@@ -1425,7 +1427,7 @@ private RangeMissingHandler metricRecordingWriter(RangeMissingHandler writer) {
             return new DelegatingRangeMissingHandler(writer) {
                 @Override
                 public SourceInputStreamFactory sharedInputStreamFactory(List<SparseFileTracker.Gap> gaps) {
-                    blobCacheMetrics.recordWrite();
+                    blobCacheMetrics.recordMiss();
                     return super.sharedInputStreamFactory(gaps);
                 }
             };

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

@@ -71,13 +71,17 @@ public void testRecordCachePopulationMetricsRecordsThroughput() {
         // let us check for 0, avoid div by 0.
         checkReadsAndMisses(0, 0, 1);
         int reads = between(1, 100);
-        int writes = between(1, reads);
-        metrics.recordWrites(writes);
-        checkReadsAndMisses(0, writes, writes);
+        int misses = between(1, reads);
+        recordMisses(metrics, misses);
+        checkReadsAndMisses(0, misses, misses);
         IntStream.range(0, reads).forEach(i -> metrics.recordRead());
-        checkReadsAndMisses(reads, writes, reads);
-        metrics.recordWrites(reads);
-        checkReadsAndMisses(reads, writes + reads, writes + reads);
+        checkReadsAndMisses(reads, misses, reads);
+        recordMisses(metrics, reads);
+        checkReadsAndMisses(reads, misses + reads, misses + reads);
+    }
+
+    private void recordMisses(BlobCacheMetrics metrics, int misses) {
+        IntStream.range(0, misses).forEach(i -> metrics.recordMiss());
     }
 
     private void checkReadsAndMisses(int reads, int writes, int readsForRatio) {