HDFS-12524. Ozone: Record number of keys scanned and hinted for getRangeKVs call. Contributed by Weiwei Yang.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/utils/LevelDBStore.java

@@ -353,11 +353,23 @@ public class LevelDBStore implements MetadataStore {
       if (dbIter != null) {
         dbIter.close();
       }
-      long end = System.currentTimeMillis();
-      long timeConsumed = end - start;
       if (LOG.isDebugEnabled()) {
-        LOG.debug("Time consumed for getRangeKVs() is {},"
+        if (filters != null) {
-                + " result length is {}.", timeConsumed, result.size());
+          for (MetadataKeyFilters.MetadataKeyFilter filter : filters) {
+            int scanned = filter.getKeysScannedNum();
+            int hinted = filter.getKeysHintedNum();
+            if (scanned > 0 || hinted > 0) {
+              LOG.debug(
+                  "getRangeKVs ({}) numOfKeysScanned={}, numOfKeysHinted={}",
+                  filter.getClass().getSimpleName(), filter.getKeysScannedNum(),
+                  filter.getKeysHintedNum());
+            }
+          }
+        }
+        long end = System.currentTimeMillis();
+        long timeConsumed = end - start;
+        LOG.debug("Time consumed for getRangeKVs() is {}ms,"
+            + " result length is {}.", timeConsumed, result.size());
       }
     }
     return result;

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/utils/MetadataKeyFilters.java

@@ -38,6 +38,14 @@ public class MetadataKeyFilters {
      * @return true if a certain condition satisfied, return false otherwise.
      */
     boolean filterKey(byte[] preKey, byte[] currentKey, byte[] nextKey);
+
+    default int getKeysScannedNum() {
+      return 0;
+    }
+
+    default int getKeysHintedNum() {
+      return 0;
+    }
   }
 
   /**
@@ -47,19 +55,37 @@ public class MetadataKeyFilters {
   public static class KeyPrefixFilter implements MetadataKeyFilter {
 
     private String keyPrefix = null;
+    private int keysScanned = 0;
+    private int keysHinted = 0;
 
     public KeyPrefixFilter(String keyPrefix) {
       this.keyPrefix = keyPrefix;
     }
 
-    @Override public boolean filterKey(byte[] preKey, byte[] currentKey,
+    @Override
+    public boolean filterKey(byte[] preKey, byte[] currentKey,
         byte[] nextKey) {
+      keysScanned++;
       if (Strings.isNullOrEmpty(keyPrefix)) {
         return true;
       } else {
-        return currentKey != null &&
+        if (currentKey != null &&
-            DFSUtil.bytes2String(currentKey).startsWith(keyPrefix);
+            DFSUtil.bytes2String(currentKey).startsWith(keyPrefix)) {
+          keysHinted++;
+          return true;
+        }
+        return false;
       }
     }
+
+    @Override
+    public int getKeysScannedNum() {
+      return keysScanned;
+    }
+
+    @Override
+    public int getKeysHintedNum() {
+      return keysHinted;
+    }
   }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/utils/RocksDBStore.java

@@ -201,11 +201,22 @@ public class RocksDBStore implements MetadataStore {
       long end = System.currentTimeMillis();
       long timeConsumed = end - start;
       if (LOG.isDebugEnabled()) {
+        if (filters != null) {
+          for (MetadataKeyFilters.MetadataKeyFilter filter : filters) {
+            int scanned = filter.getKeysScannedNum();
+            int hinted = filter.getKeysHintedNum();
+            if (scanned > 0 || hinted > 0) {
+              LOG.debug(
+                  "getRangeKVs ({}) numOfKeysScanned={}, numOfKeysHinted={}",
+                  filter.getClass().getSimpleName(), filter.getKeysScannedNum(),
+                  filter.getKeysHintedNum());
+            }
+          }
+        }
         LOG.debug("Time consumed for getRangeKVs() is {}ms,"
             + " result length is {}.", timeConsumed, result.size());
       }
     }
-
     return result;
   }
 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/ozone/TestMetadataStore.java

@@ -265,6 +265,8 @@ public class TestMetadataStore {
     Assert.assertTrue(result.stream().allMatch(entry ->
         new String(entry.getKey()).startsWith("b")
     ));
+    Assert.assertEquals(20, filter1.getKeysScannedNum());
+    Assert.assertEquals(10, filter1.getKeysHintedNum());
     result = store.getRangeKVs(null, 3, filter1);
     Assert.assertEquals(3, result.size());
     result = store.getRangeKVs(getBytes("b3"), 1, filter1);