farmmamba created HDFS-17085:
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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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