[GitHub] [hadoop] anoopsjohn commented on a change in pull request #3149: HADOOP-17770 WASB : Support disabling buffered reads in positional reads

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

anoopsjohn commented on a change in pull request #3149:
URL: https://github.com/apache/hadoop/pull/3149#discussion_r667094175



##########
File path: hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azure/NativeAzureFileSystem.java
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@@ -915,6 +922,33 @@ public synchronized int read(byte[] b, int off, int len) throws FileNotFoundExce
       }
     }
 
+    @Override
+    public int read(long position, byte[] buffer, int offset, int length)
+        throws IOException {
+      if (in instanceof PositionedReadable) {
+        try {
+          int result = ((PositionedReadable) this.in).read(position, buffer,
+              offset, length);
+          if (null != statistics && result > 0) {
+            statistics.incrementBytesRead(result);
+          }
+          return result;
+        } catch (IOException e) {
+          Throwable innerException = NativeAzureFileSystemHelper.checkForAzureStorageException(e);
+          if (innerException instanceof StorageException) {
+            LOG.error("Encountered Storage Exception for read on Blob : {}"
+                + " Exception details: {} Error Code : {}",
+                key, e, ((StorageException) innerException).getErrorCode());
+            if (NativeAzureFileSystemHelper.isFileNotFoundException((StorageException) innerException)) {
+              throw new FileNotFoundException(String.format("%s is not found", key));
+            }
+          }
+          throw e;
+        }
+      }
+      return super.read(position, buffer, offset, length);

Review comment:
       Before this patch it happen this way.
   FSInputStream.read(long, byte[], int, int)
   You are right that FSInputStream pread API do relative read.  But in finally it seek back to original pos
   ya after this patch the 'in' will be PositionedReadable for sure.  But I think we should keep this generic way
   If here 'in' is PositionedReadable make use of that pread API or else fallback to old way




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