steveloughran commented on code in PR #7662:
URL: https://github.com/apache/hadoop/pull/7662#discussion_r2068923434


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hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3ABlockOutputStream.java:
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@@ -829,7 +829,8 @@ public boolean hasCapability(String capability) {
   @Override
   public void hflush() throws IOException {
     statistics.hflushInvoked();
-    handleSyncableInvocation();
+    // do not reject these, but downgrade to a no-oop
+    LOG.debug("Hflush invoked");

Review Comment:
   look at the fs spec. we say "don't use the api and highlight the 
inconsistent outcomes"
   
   The semantics of hflush say "visible to all" but no persistence, so it's not 
changing any durability semantics. Are we changing the visibility? we're 
certainly not meeting them. 
   
   I remember having a long talk with others about hflush, as in "what does it 
do?" -the answer is "nothing you can rely on". 
   
   when exceptions are downgraded (default) all that happens is the log message 
is removed, so reducing confusion.
   
   when exceptions are rejected, the failure goes away. The one I want to fail 
here is hsync(), and at holds. AFAIK nobody runs with that flag on except for 
some of our test setups. 
   
   ---- 
   
   ### `Syncable.hflush()`
   
   Flush out the data in client's user buffer. After the return of
   this call, new readers will see the data. The `hflush()` operation
   does not contain any guarantees as to the durability of the data. only
   its visibility.
   
   Thus implementations may cache the written data in memory
   —visible to all, but not yet persisted.
   



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