[GitHub] sohami commented on a change in pull request #1296: DRILL-5365: Prevent plugin config from changing default fs. Make DrillFileSystem Immutable.

[GitBox <gi...@apache.org>]

sohami commented on a change in pull request #1296: DRILL-5365: Prevent plugin config from changing default fs. Make DrillFileSystem Immutable.
URL: https://github.com/apache/drill/pull/1296#discussion_r203504583
 
 

 ##########
 File path: exec/java-exec/src/main/java/org/apache/drill/exec/store/dfs/DrillFileSystemCache.java
 ##########
 @@ -0,0 +1,99 @@
+/*
+ * 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.drill.exec.store.dfs;
+
+import com.google.common.base.Preconditions;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FileSystem;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * <h4>Motivation</h4>
+ * <p>
+ *   This cache is intended to work around the bugs in the {@link org.apache.hadoop.fs.FileSystem} static cache (DRILL-5365). Specifically, as of Hadoop 2.7.x the
+ *   {@link org.apache.hadoop.fs.FileSystem} cache has the following bad behavior:
+ * </p>
+ * <ul>
+ *   <li>
+ *     The {@link org.apache.hadoop.conf.Configuration} object is not considered when constructing keys for the {@link org.apache.hadoop.fs.FileSystem} cache of
+ *     {@link org.apache.hadoop.fs.FileSystem} objects.
+ *   </li>
+ *   <li>
+ *      The {@link org.apache.hadoop.fs.FileSystem} cache does not honor the <b>fs.default.name</b> property when constructing keys, only <b>fs.defaultFS</b> is used to construct
+ *      keys in the cache.
+ *   </li>
+ * </ul>
+ *
+ * <h4>Usage</h4>
+ *
+ * <ul>
+ *   <li>
+ *     A prerequisite for usage is that all {@link org.apache.hadoop.conf.Configuration} objects are normalized with
+ *     {@link org.apache.drill.exec.store.dfs.DrillFileSystem#normalize(Configuration)}.
+ *   </li>
+ *   <li>
+ *     This cache should only be used from {@link org.apache.drill.exec.store.dfs.DrillFileSystem}.
+ *   </li>
+ * </ul>
+ *
+ * <h4>TODO</h4>
+ *
+ * <ul>
+ *   <li>
+ *     Drill currently keeps a {@link org.apache.drill.exec.store.dfs.DrillFileSystem} open indefinitely. This will be corrected
+ *     in DRILL-6608. As a result this cache currently has no methods to remove {@link org.apache.hadoop.fs.FileSystem} objects
+ *     after they are created.
+ *   </li>
+ * </ul>
+ */
+class DrillFileSystemCache {
+  private Map<Map<String, String>, FileSystem> cache = new HashMap<>();
+
+  /**
+   * If a {@link org.apache.hadoop.fs.FileSystem} object corresponding to the given {@link org.apache.hadoop.conf.Configuration}
+   * exists in the cache, then it is returned. If no corresponding {@link org.apache.hadoop.fs.FileSystem} exist, then it is created,
+   * added to the cache, and returned.
+   * @param configuration The {@link org.apache.hadoop.conf.Configuration} corresponding to the desired {@link org.apache.hadoop.fs.FileSystem}
+   *                      object. It is expected that this configuration is first normalized with {@link org.apache.drill.exec.store.dfs.DrillFileSystem#normalize(Configuration)}.
+   * @return The {@link org.apache.hadoop.fs.FileSystem} object corresponding to he given {@link org.apache.hadoop.conf.Configuration}.
+   * @throws IOException An error when creating the desired {@link org.apache.hadoop.fs.FileSystem} object.
+   */
+  protected synchronized FileSystem get(final Configuration configuration) throws IOException {
+    final Map<String, String> map = new HashMap<>(configToMap(configuration));
+
+    if (!cache.containsKey(map)) {
+      cache.put(map, FileSystem.newInstance(configuration));
+    }
+
+    return cache.get(map);
+  }
+
+  static Map<String, String> configToMap(final Configuration configuration) {
+    Preconditions.checkNotNull(configuration);
+    final Map<String, String> map = new HashMap<>();
+
+    for (Map.Entry<String, String> entry: configuration) {
+      map.put(entry.getKey().trim(), entry.getValue());
 
 Review comment:
   In this implementation we are only considering `Configuration` object in Cache key. How about other parameters which [HadoopFileSystem cache](https://github.com/apache/hadoop/blob/branch-2.7.1/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FileSystem.java#L2812) is using ? Specially I am concerned about the UGI object from which the user information is retrieved which is later checked for access control.
   
   Also for handling `fs.default.name` and `fs.defaultFS` once it's set in the configuration parameter and FileSystem instance is created then [FileSystemCache does use information from there based on UR](https://github.com/apache/hadoop/blob/branch-2.7.1/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FileSystem.java#L2806)I (which is created using those parameters).

----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on GitHub and use the
URL above to go to the specific comment.
 
For queries about this service, please contact Infrastructure at:
users@infra.apache.org


With regards,
Apache Git Services