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https://issues.apache.org/jira/browse/HBASE-15077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15089148#comment-15089148
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ramkrishna.s.vasudevan commented on HBASE-15077:
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+1 on patch.
> Support OffheapKV write in compaction with out copying data on heap
> -------------------------------------------------------------------
>
> Key: HBASE-15077
> URL: https://issues.apache.org/jira/browse/HBASE-15077
> Project: HBase
> Issue Type: Sub-task
> Components: regionserver, Scanners
> Reporter: Anoop Sam John
> Assignee: Anoop Sam John
> Fix For: 2.0.0
>
> Attachments: HBASE-15077.patch, HBASE-15077_V2.patch
>
>
> HBASE-14832 is not enough to handle this. Doing the remaining needed here.
> {code}
> if (cell instanceof ByteBufferedCell) {
> 890 out.writeShort(rowLen);
> 891 ByteBufferUtils.copyBufferToStream(out, ((ByteBufferedCell)
> cell).getRowByteBuffer(),
> 892 ((ByteBufferedCell) cell).getRowPosition(), rowLen);
> 893 out.writeByte(fLen);
> 894 ByteBufferUtils.copyBufferToStream(out, ((ByteBufferedCell)
> cell).getFamilyByteBuffer(),
> 895 ((ByteBufferedCell) cell).getFamilyPosition(), fLen);
> 896 ByteBufferUtils.copyBufferToStream(out, ((ByteBufferedCell)
> cell).getQualifierByteBuffer(),
> 897 ((ByteBufferedCell) cell).getQualifierPosition(), qLen);
> {code}
> We have done this but it is not really helping us!
> In ByteBufferUtils#copyBufferToStream
> {code}
> public static void copyBufferToStream(OutputStream out, ByteBuffer in,
> int offset, int length) throws IOException {
> if (in.hasArray()) {
> out.write(in.array(), in.arrayOffset() + offset,
> length);
> } else {
> for (int i = 0; i < length; ++i) {
> out.write(toByte(in, offset + i));
> }
> }
> }
> {code}
> So for DBB it is so costly op writing byte by byte reading each to on heap.
> Even if we use writeByteBuffer(OutputStream out, ByteBuffer b, int offset,
> int length), it won't help us as the underlying stream is a
> ByteArrayOutputStream and so we will end up in copying.
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