[GitHub] [tez] steveloughran commented on a diff in pull request #274: TEZ-4479: Eagerly Init/Load FileSystem In Tez Task Containers

["steveloughran (via GitHub)" <gi...@apache.org>]

steveloughran commented on code in PR #274:
URL: https://github.com/apache/tez/pull/274#discussion_r1149332283


##########
tez-runtime-internals/src/main/java/org/apache/tez/runtime/task/TezChild.java:
##########
@@ -503,6 +506,33 @@ public static TezChild newTezChild(Configuration conf, String host, int port, St
         hadoopShim);
   }
 
+  private static void eagerInitFileSystemPaths(Configuration conf) {
+    Collection<String> eagerInitPaths = conf.getTrimmedStringCollection(
+        TezConfiguration.TEZ_TASK_EAGER_INIT_FS_PATHS);
+    if (eagerInitFsPool == null && !eagerInitPaths.isEmpty()) {
+      eagerInitFsPool = Executors.newCachedThreadPool(new ThreadFactoryBuilder()
+          .setDaemon(true)
+          .setNameFormat("Eager-Init-Fs-Thread-%d")
+          .build());
+    }
+    for (String path : eagerInitPaths) {
+      eagerInitFsPool.execute(new Runnable() {

Review Comment:
   before rushing to create lots of fs instances in parallel, look at HADOOP-17313 and why we actually added semaphores to stop apps like tez creating too many at the same time. this code may cause overload problems, or the fs semaphore will hold you back for safety.
   
   best to look at why its taking so long; if s3a bucket existence checks aren't involved, then it'll be whatever auth mechanism is plugged in. same for abfs



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