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https://issues.apache.org/jira/browse/HADOOP-18184?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17746939#comment-17746939
 ] 

ASF GitHub Bot commented on HADOOP-18184:
-----------------------------------------

steveloughran commented on code in PR #5832:
URL: https://github.com/apache/hadoop/pull/5832#discussion_r1273419854


##########
hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/prefetch/S3ARemoteInputStream.java:
##########
@@ -409,27 +455,54 @@ protected String getOffsetStr(long offset) {
     return String.format("%d:%d", blockNumber, offset);
   }
 
+  @Override
+  public synchronized void unbuffer() {
+    LOG.debug("{}: unbuffered", getName());
+    if (closeStream(true)) {
+      getS3AStreamStatistics().unbuffered();
+    }
+  }
+
+  /**
+   * Close the stream in close() or unbuffer().
+   * @param unbuffer is this an unbuffer operation?
+   * @return true if the stream was closed; false means it was already closed.
+   */
+  protected boolean closeStream(final boolean unbuffer) {
+
+    if (underlyingResourcesClosed.getAndSet(true)) {
+      return false;
+    }
+
+    if (unbuffer) {

Review Comment:
   done





> s3a prefetching stream to support unbuffer()
> --------------------------------------------
>
>                 Key: HADOOP-18184
>                 URL: https://issues.apache.org/jira/browse/HADOOP-18184
>             Project: Hadoop Common
>          Issue Type: Sub-task
>          Components: fs/s3
>    Affects Versions: 3.4.0
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>            Priority: Minor
>              Labels: pull-request-available
>
> Apache Impala uses unbuffer() to free up all client side resources held by a 
> stream, so allowing it to have a map of available (path -> stream) objects, 
> retained across queries.
> This saves on having to reopen the files, with the cost of HEAD checks etc. 
> S3AInputStream just closes its http connection. here there is a lot more 
> state to discard, but all memory and file storage must be freed.
> until this done, ITestS3AContractUnbuffer must skip when the prefetch stream 
> is used.
> its notable that the other tests don't fail, even though the stream doesn't 
> implement the interface; the graceful degradation handles that. it should 
> fail if the test xml resource says the stream does it, but that the stream 
> capabilities say it doesn't.



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