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Subject [GitHub] [hadoop] DadanielZ commented on a change in pull request #1898: HADOOP-16852: Report read-ahead error back
Date Sun, 29 Mar 2020 00:22:48 GMT
DadanielZ commented on a change in pull request #1898: HADOOP-16852: Report read-ahead error
URL: https://github.com/apache/hadoop/pull/1898#discussion_r399725608

 File path: hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azurebfs/services/ReadBufferManager.java
 @@ -299,11 +327,32 @@ private void clearFromReadAheadQueue(final AbfsInputStream stream,
final long re
   private int getBlockFromCompletedQueue(final AbfsInputStream stream, final long position,
final int length,
-                                         final byte[] buffer) {
-    ReadBuffer buf = getFromList(completedReadList, stream, position);
-    if (buf == null || position >= buf.getOffset() + buf.getLength()) {
+                                         final byte[] buffer) throws IOException {
+    ReadBuffer buf = getBufferFromCompletedQueue(stream, position);
+    if (buf == null) {
       return 0;
+    if (buf.getStatus() == ReadBufferStatus.READ_FAILED) {
+      // Eviction of a read buffer is triggered only when a queue request comes in
+      // and each eviction attempt tries to find one eligible buffer.
+      // Hence there are chances that an old read-ahead buffer with exception is still
+      // available. To prevent new read requests to fail due to such old buffers,
+      // return exception only from buffers that failed within last THRESHOLD_AGE_MILLISECONDS
+      if ((currentTimeMillis() - (buf.getTimeStamp()) < THRESHOLD_AGE_MILLISECONDS)) {
 Review comment:
   If this is to avoid the failure for new requests, then instead of checking the time window,
why not  reset the buffer status before throwing the exception? Then following new requests
will not be affected by the old failure.

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