[jira] [Created] (HDFS-17085) Erasure coding: readTo is computed large than actually needed during pread

["farmmamba (Jira)" <ji...@apache.org>]

farmmamba created HDFS-17085:
--------------------------------

             Summary: Erasure coding: readTo is computed large than actually needed during pread
                 Key: HDFS-17085
                 URL: https://issues.apache.org/jira/browse/HDFS-17085
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: erasure-coding
    Affects Versions: 3.4.0
            Reporter: farmmamba


In HDFS-16520，it improved EC pread by introducing a readTo field.

But, the way it was calculated seems still have some room for improvement.

Now, it was calculated by below code:
{code:java}
for (AlignedStripe stripe : stripes) {
  readTo = Math.max(readTo, stripe.getOffsetInBlock() + stripe.getSpanInBlock());
} {code}
But in the followed code, for every AlignedStripe object, it uses max readTo to construct StripeReader. I think there still exists waste of resource.
{code:java}
for (AlignedStripe stripe : stripes) {
  // Parse group to get chosen DN location
  StripeReader preader = new PositionStripeReader(stripe, ecPolicy, blks,
      preaderInfos, corruptedBlocks, decoder, this);
  preader.setReadTo(readTo);
  try {
    preader.readStripe();
  } finally {
    preader.close();
  }
} {code}



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