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https://issues.apache.org/jira/browse/HADOOP-11847?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14508494#comment-14508494
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Kai Zheng commented on HADOOP-11847:
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bq.Is decodingByteArrayBuffersForInput always filled with zero bytes? I don't
see where it's filled with actual data
It's filled with ZERO bytes as below:
{code}
+ // Ensure only ZERO bytes are read from
+ for (int i = 0; i < decodingByteArrayBuffersForInput.length; ++i) {
+ System.arraycopy(ZERO_BYTES, 0, decodingByteArrayBuffersForInput[i],
+ 0, ZERO_BYTES.length);
+ }
{code}
It's used in the following codes:
{code}
+ for (int i = 0; i < inputs.length; i++) {
+ if (inputs[i] != null) {
+ decodingByteArrayInputs[i] = inputs[i];
+ } else {
+ // Borrow it from decodingByteArrayBuffersForInput for the temp usage.
+ decodingByteArrayInputs[i] = decodingByteArrayBuffersForInput[idx];
+ decodingErasedIndexes[idx++] = i;
+ }
+ }
{code}
> Enhance raw coder allowing to read least required inputs in decoding
> --------------------------------------------------------------------
>
> Key: HADOOP-11847
> URL: https://issues.apache.org/jira/browse/HADOOP-11847
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: io
> Reporter: Kai Zheng
> Assignee: Kai Zheng
> Attachments: HADOOP-11847-v1.patch, HADOOP-11847-v2.patch
>
>
> This is to enhance raw erasure coder to allow only reading least required
> inputs while decoding. It will also refine and document the relevant APIs for
> better understanding and usage. When using least required inputs, it may add
> computating overhead but will possiblly outperform overall since less network
> traffic and disk IO are involved.
> This is something planned to do but just got reminded by [~zhz]' s question
> raised in HDFS-7678, also copied here:
> bq.Kai Zheng I have a question about decoding: in a (6+3) schema, if block #2
> is missing, and I want to repair it with blocks 0, 1, 3, 4, 5, 8, how should
> I construct the inputs to RawErasureDecoder#decode?
> With this work, hopefully the answer to above question would be obvious.
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