HDDS-10206. Expose jmx metrics for snapshot cache size on the ozone manager.

hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/OMMetrics.java

@@ -25,6 +25,7 @@
 import org.apache.hadoop.metrics2.annotation.Metric;
 import org.apache.hadoop.metrics2.annotation.Metrics;
 import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
+import org.apache.hadoop.metrics2.lib.MutableCounterInt;
 import org.apache.hadoop.metrics2.lib.MutableCounterLong;
 
 /**
@@ -74,7 +75,7 @@ public class OMMetrics implements OmMetadataReaderMetrics {
   private @Metric MutableCounterLong numSnapshotLists;
   private @Metric MutableCounterLong numSnapshotDiffJobs;
   private @Metric MutableCounterLong numSnapshotInfos;
-
+  private @Metric MutableCounterInt numSnapshotCacheSize;
   private @Metric MutableCounterLong numGetFileStatus;
   private @Metric MutableCounterLong numCreateDirectory;
   private @Metric MutableCounterLong numCreateFile;
@@ -520,6 +521,19 @@ public void decNumSnapshotDeleted() {
     numSnapshotDeleted.incr(-1);
   }
 
+  public void setNumSnapshotCacheSize(int num) {
+    int curVal = numSnapshotCacheSize.value();
+    numSnapshotCacheSize.incr(num - curVal);
+  }
+
+  public void incNumSnapshotCacheSize() {
+    numSnapshotCacheSize.incr();
+  }
+
+  public void decNumSnapshotCacheSize() {
+    numSnapshotCacheSize.incr(-1);
+  }
+
   public void incNumCompleteMultipartUploadFails() {
     numCompleteMultipartUploadFails.incr();
   }

hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/OmSnapshotManager.java

@@ -418,6 +418,7 @@ public int getSnapshotCacheSize() {
   public void invalidateCache() {
     if (snapshotCache != null) {
       snapshotCache.invalidateAll();
+      updateSnapshotCacheSizeMetric();
     }
   }
 
@@ -429,6 +430,7 @@ public void invalidateCache() {
   public void invalidateCacheEntry(UUID key) throws IOException {
     if (snapshotCache != null) {
       snapshotCache.invalidate(key);
+      updateSnapshotCacheSizeMetric();
     }
   }
 
@@ -679,7 +681,9 @@ private ReferenceCounted<OmSnapshot> getSnapshot(String snapshotTableKey, boolea
     }
 
     // retrieve the snapshot from the cache
-    return snapshotCache.get(snapshotInfo.getSnapshotId());
+    ReferenceCounted<OmSnapshot> snapshot = snapshotCache.get(snapshotInfo.getSnapshotId());
+    updateSnapshotCacheSizeMetric();
+    return snapshot;
   }
 
   /**
@@ -977,4 +981,11 @@ public void close() {
   public long getDiffCleanupServiceInterval() {
     return diffCleanupServiceInterval;
   }
+
+  /**
+   * Updates the SnapshotCache size jmx metric.
+   */
+  public void updateSnapshotCacheSizeMetric() {
+    this.ozoneManager.getMetrics().setNumSnapshotCacheSize(getSnapshotCacheSize());
+  }
 }

hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/OzoneManager.java

@@ -856,6 +856,7 @@ private void instantiateServices(boolean withNewSnapshot) throws IOException {
     omSnapshotManager = new OmSnapshotManager(this);
 
     // Snapshot metrics
+    metrics.setNumSnapshotCacheSize(omSnapshotManager.getSnapshotCacheSize());
     updateActiveSnapshotMetrics();
 
     if (withNewSnapshot) {
@@ -1801,7 +1802,6 @@ private void updateActiveSnapshotMetrics()
         }
       }
     }
-
     metrics.setNumSnapshotActive(activeGauge);
     metrics.setNumSnapshotDeleted(deletedGauge);
   }

hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/snapshot/SnapshotCache.java

@@ -157,7 +157,6 @@ public ReferenceCounted<OmSnapshot> get(UUID key) throws IOException {
           }
           return v;
         });
-
     if (rcOmSnapshot == null) {
       // The only exception that would fall through the loader logic above
       // is OMException with FILE_NOT_FOUND.