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https://issues.apache.org/jira/browse/HADOOP-18146?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17651160#comment-17651160
 ] 

ASF GitHub Bot commented on HADOOP-18146:
-----------------------------------------

anmolanmol1234 commented on code in PR #4039:
URL: https://github.com/apache/hadoop/pull/4039#discussion_r1055218825


##########
hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azurebfs/services/AbfsHttpOperation.java:
##########
@@ -314,13 +327,46 @@ public void sendRequest(byte[] buffer, int offset, int 
length) throws IOExceptio
     if (this.isTraceEnabled) {
       startTime = System.nanoTime();
     }
-    try (OutputStream outputStream = this.connection.getOutputStream()) {
-      // update bytes sent before they are sent so we may observe
-      // attempted sends as well as successful sends via the
-      // accompanying statusCode
+    OutputStream outputStream = null;
+    // Updates the expected bytes to be sent based on length.
+    this.expectedBytesToBeSent = length;
+    try {
+      try {
+        /* Without expect header enabled, if getOutputStream() throws
+           an exception, it gets caught by the restOperation. But with
+           expect header enabled we return back without throwing an exception
+           for the correct response code processing.
+         */
+        outputStream = this.connection.getOutputStream();
+      } catch (IOException e) {
+        /* If getOutputStream fails with an exception and expect header
+           is enabled, we return back without throwing an exception to
+           the caller. The caller is responsible for setting the correct 
status code.
+           If expect header is not enabled, we throw back the exception.
+         */
+        String expectHeader = this.connection.getRequestProperty(EXPECT);
+        if (expectHeader != null && expectHeader.equals(HUNDRED_CONTINUE)) {
+          LOG.debug("Getting output stream failed with expect header enabled, 
returning back "
+                  + ExceptionUtils.getStackTrace(e));
+          return;

Review Comment:
   The request was sent to the server with expect header enabled but it didn't 
respond back with 100-continue because client didn't meet with the 
expectations. So the connection was successfully set and hence it can set all 
these properties accordingly.





> ABFS: Add changes for expect hundred continue header with append requests
> -------------------------------------------------------------------------
>
>                 Key: HADOOP-18146
>                 URL: https://issues.apache.org/jira/browse/HADOOP-18146
>             Project: Hadoop Common
>          Issue Type: Sub-task
>    Affects Versions: 3.3.1
>            Reporter: Anmol Asrani
>            Assignee: Anmol Asrani
>            Priority: Major
>              Labels: pull-request-available
>          Time Spent: 2h 10m
>  Remaining Estimate: 0h
>
>  Heavy load from a Hadoop cluster lead to high resource utilization at FE 
> nodes. Investigations from the server side indicate payload buffering at 
> Http.Sys as the cause. Payload of requests that eventually fail due to 
> throttling limits are also getting buffered, as its triggered before FE could 
> start request processing.
> Approach: Client sends Append Http request with Expect header, but holds back 
> on payload transmission until server replies back with HTTP 100. We add this 
> header for all append requests so as to reduce.
> We made several workload runs with and without hundred continue enabled and 
> the overall observation is that :-
>  # The ratio of TCP SYN packet count with and without expect hundred continue 
> enabled is 0.32 : 3 on average.
>  #  The ingress into the machine at TCP level is almost 3 times lesser with 
> hundred continue enabled which implies a lot of bandwidth save.



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