HDDS-2364. Add OM metrics to find the false positive rate for the keyMayExist.

hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/utils/db/RDBMetrics.java

@@ -0,0 +1,75 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 org.apache.hadoop.hdds.utils.db;
+
+import org.apache.hadoop.metrics2.MetricsSystem;
+import org.apache.hadoop.metrics2.annotation.Metric;
+import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
+import org.apache.hadoop.metrics2.lib.MutableCounterLong;
+
+import com.google.common.annotations.VisibleForTesting;
+
+/**
+ * Class to hold RocksDB metrics.
+ */
+public class RDBMetrics {
+
+  private static final String SOURCE_NAME =
+      RDBMetrics.class.getSimpleName();
+
+  public RDBMetrics() {
+  }
+
+  public static RDBMetrics create() {
+    MetricsSystem ms = DefaultMetricsSystem.instance();
+    return ms.register(SOURCE_NAME,
+        "Rocks DB Metrics",
+        new RDBMetrics());
+  }
+
+  private @Metric MutableCounterLong numDBKeyMayExistChecks;
+  private @Metric MutableCounterLong numDBKeyMayExistMisses;
+
+
+  public void incNumDBKeyMayExistChecks() {
+    numDBKeyMayExistChecks.incr();
+  }
+
+  public void incNumDBKeyMayExistMisses() {
+    numDBKeyMayExistMisses.incr();
+  }
+
+
+  @VisibleForTesting
+  public long getNumDBKeyMayExistChecks() {
+    return numDBKeyMayExistChecks.value();
+  }
+
+  @VisibleForTesting
+  public long getNumDBKeyMayExistMisses() {
+    return numDBKeyMayExistMisses.value();
+  }
+
+  public void unRegister() {
+    MetricsSystem ms = DefaultMetricsSystem.instance();
+    ms.unregisterSource(SOURCE_NAME);
+  }
+
+}

hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/utils/db/RDBStore.java

@@ -67,6 +67,7 @@ public class RDBStore implements DBStore {
   private RDBCheckpointManager checkPointManager;
   private String checkpointsParentDir;
   private List<ColumnFamilyHandle> columnFamilyHandles;
+  private RDBMetrics rdbMetrics;
 
   @VisibleForTesting
   public RDBStore(File dbFile, DBOptions options,
@@ -131,6 +132,7 @@ public RDBStore(File dbFile, DBOptions options,
 
       //Initialize checkpoint manager
       checkPointManager = new RDBCheckpointManager(db, "om");
+      rdbMetrics = RDBMetrics.create();
 
     } catch (RocksDBException e) {
       throw toIOException(
@@ -252,7 +254,7 @@ public Table<byte[], byte[]> getTable(String name) throws IOException {
     if (handle == null) {
       throw new IOException("No such table in this DB. TableName : " + name);
     }
-    return new RDBTable(this.db, handle, this.writeOptions);
+    return new RDBTable(this.db, handle, this.writeOptions, rdbMetrics);
   }
 
   @Override
@@ -274,7 +276,7 @@ public <KEY, VALUE> Table<KEY, VALUE> getTable(String name,
   public ArrayList<Table> listTables() throws IOException {
     ArrayList<Table> returnList = new ArrayList<>();
     for (ColumnFamilyHandle handle : handleTable.values()) {
-      returnList.add(new RDBTable(db, handle, writeOptions));
+      returnList.add(new RDBTable(db, handle, writeOptions, rdbMetrics));
     }
     return returnList;
   }
@@ -378,4 +380,7 @@ public RocksDB getDb() {
     return db;
   }
 
+  public RDBMetrics getMetrics() {
+    return rdbMetrics;
+  }
 }

hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/utils/db/RDBTable.java

@@ -48,6 +48,7 @@ class RDBTable implements Table<byte[], byte[]> {
   private final RocksDB db;
   private final ColumnFamilyHandle handle;
   private final WriteOptions writeOptions;
+  private final RDBMetrics rdbMetrics;
 
   /**
    * Constructs a TableStore.
@@ -57,10 +58,11 @@ class RDBTable implements Table<byte[], byte[]> {
    * @param writeOptions - RocksDB write Options.
    */
   RDBTable(RocksDB db, ColumnFamilyHandle handle,
-      WriteOptions writeOptions) {
+      WriteOptions writeOptions, RDBMetrics rdbMetrics) {
     this.db = db;
     this.handle = handle;
     this.writeOptions = writeOptions;
+    this.rdbMetrics = rdbMetrics;
   }
 
   /**
@@ -125,8 +127,17 @@ public boolean isExist(byte[] key) throws IOException {
       // RocksDB#keyMayExist
       // If the key definitely does not exist in the database, then this
       // method returns false, else true.
-      return db.keyMayExist(handle, key, new StringBuilder())
-          && db.get(handle, key) != null;
+      rdbMetrics.incNumDBKeyMayExistChecks();
+      boolean keyMayExist = db.keyMayExist(handle, key, new StringBuilder());
+      if (!keyMayExist) {
+        return false;
+      } else {
+        boolean keyGet = (db.get(handle, key) != null);
+        if (!keyGet) {
+          rdbMetrics.incNumDBKeyMayExistMisses();
+        }
+        return keyGet;
+      }
     } catch (RocksDBException e) {
       throw toIOException(
           "Error in accessing DB. ", e);

hadoop-hdds/common/src/test/java/org/apache/hadoop/hdds/utils/db/TestRDBTableStore.java

@@ -246,6 +246,9 @@ public void testIsExist() throws Exception {
       byte[] invalidKey =
           RandomStringUtils.random(5).getBytes(StandardCharsets.UTF_8);
       Assert.assertFalse(testTable.isExist(invalidKey));
+      RDBMetrics rdbMetrics = rdbStore.getMetrics();
+      Assert.assertEquals(3, rdbMetrics.getNumDBKeyMayExistChecks());
+      Assert.assertTrue(rdbMetrics.getNumDBKeyMayExistMisses() <= 1);
     }
   }