[GitHub] [hbase] ndimiduk commented on a change in pull request #2034: Backport "HBASE-24625 AsyncFSWAL.getLogFileSizeIfBeingWritten does not return the expected synced file length. (#1970)" to branch-2

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

ndimiduk commented on a change in pull request #2034:
URL: https://github.com/apache/hbase/pull/2034#discussion_r452529869



##########
File path: hbase-asyncfs/src/main/java/org/apache/hadoop/hbase/io/asyncfs/WrapperAsyncFSOutput.java
##########
@@ -91,7 +93,11 @@ private void flush0(CompletableFuture<Long> future, ByteArrayOutputStream buffer
           out.hflush();
         }
       }
-      future.complete(out.getPos());
+      long pos = out.getPos();
+      if(pos > this.syncedLength) {

Review comment:
       I had asked in #1970 if this can be implemented with an `AtomicLong` instead. @Apache9 responded with an analysis and alternative suggestion. Following his suggestion, it would be nice to add a comment on `WrapperAsyncFSOutput` stating that we expect an instance to be used only from a single thread, foregoing synchronization for the sake of performance.

##########
File path: hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/AsyncProtobufLogWriter.java
##########
@@ -231,4 +231,9 @@ protected long writeWALTrailerAndMagic(WALTrailer trailer, byte[] magic) throws
   protected OutputStream getOutputStreamForCellEncoder() {
     return asyncOutputWrapper;
   }
+
+  @Override
+  public long getSyncedLength() {
+    return this.output.getSyncedLength();

Review comment:
       nit: `this` is unnecessary.

##########
File path: hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/ProtobufLogWriter.java
##########
@@ -85,6 +90,12 @@ public void sync(boolean forceSync) throws IOException {
     } else {
       fsdos.hflush();
     }
+    AtomicUtils.updateMax(this.syncedLength, fsdos.getPos());

Review comment:
       I believe I mentioned elsewhere that I think `AtomicUtils.updateMax` can be replaced with [`AtomicLong.getAndAccumulate`](https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicLong.html#getAndAccumulate-long-java.util.function.LongBinaryOperator-), something like
   ```
   syncedLength.getAndAccumulate(fsdos.getPos(), Math::max)
   ```




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