import quincy 17.2.0

[ceph.git] / ceph / src / arrow / java / vector / src / main / java / org / apache / arrow / vector / NullCheckingForGet.java

diff --git a/ceph/src/arrow/java/vector/src/main/java/org/apache/arrow/vector/NullCheckingForGet.java b/ceph/src/arrow/java/vector/src/main/java/org/apache/arrow/vector/NullCheckingForGet.java
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+/*
+ * 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.arrow.vector;
+
+/**
+ * Configuration class to determine if null checking should be enabled or disabled for the "get" methods.
+ * For example, the get method of class org.apache.arrow.vector.Float8Vector first checks if the value
+ * at the given index is null, before retrieving the value. This configuration will turn on and off such checks.
+ *
+ * <p>Null checking is on by default. You can disable it by setting either the system property or the
+ * environmental variable to "false". The system property is named "arrow.enable_null_check_for_get" and
+ * the environmental variable is named "ARROW_ENABLE_NULL_CHECK_FOR_GET".
+ * When both the system property and the environmental variable are set, the system property takes precedence.
+ * </p>
+ * <p>
+ * Disabling null-checking in the "get" methods may lead to performance improvements.
+ * For example, suppose we have the following micro-benchmark:
+ * </p>
+ * <p>
+ * <pre>{@code
+ *
+ *   Float8Vector vector = ...
+ *
+ *   public void test() {
+ *     sum = 0;
+ *     for (int i = 0; i < 1024; i++) {
+ *       vector.set(i, i + 10.0);
+ *       safeSum += vector.get(i);
+ *     }
+ *   }
+ *
+ * }</pre>
+ * </p>
+ * <p>
+ * Performance evaluations of the micro-benchmark with the JMH framework reveal that, disabling null checking
+ * has the following effects:
+ * 1. The amounts of byte code and assembly code generated by JIT are both smaller.
+ * 2. The performance improves by about 30% (2.819 ± 0.005  us/op vs. 4.069 ± 0.004  us/op).
+ * </p>
+ * <p>
+ * Therefore, for scenarios where the user can be sure that the null-checking is unnecessary,
+ * it is beneficial to disable it with this configuration.
+ * </p>
+ */
+public class NullCheckingForGet {
+
+  /**
+   * The flag to indicate if null checking is enabled for "get" methods.
+   */
+  public static final boolean NULL_CHECKING_ENABLED;
+
+  static {
+    String envProperty = System.getenv("ARROW_ENABLE_NULL_CHECK_FOR_GET");
+    String sysProperty = System.getProperty("arrow.enable_null_check_for_get");
+
+    // The system property has a higher priority than the environmental variable.
+    String flagValue = sysProperty;
+    if (flagValue == null) {
+      flagValue = envProperty;
+    }
+
+    // The flag is set to false only if the system property/environmental
+    // variable is explicitly set to "false".
+    NULL_CHECKING_ENABLED = !"false".equals(flagValue);
+  }
+
+  private NullCheckingForGet() {
+  }
+}