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https://issues.apache.org/jira/browse/HBASE-14186?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14654201#comment-14654201
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stack commented on HBASE-14186:
-------------------------------
Excellent.
Here, if (remaining >= Bytes.SIZEOF_INT) {.... Is it possible, that
we could come in here and there'd only be a short amount to read so we'd skip
the SIZEOF_INT parens? if so, the shift by 16 bits in the second paren would
be not needed (might not be a problem if left shifting 0)?
Otherwise, +1. Nice.
> Read mvcc vlong optimization
> ----------------------------
>
> Key: HBASE-14186
> URL: https://issues.apache.org/jira/browse/HBASE-14186
> Project: HBase
> Issue Type: Sub-task
> Components: Scanners
> Reporter: Anoop Sam John
> Assignee: Anoop Sam John
> Fix For: 2.0.0
>
> Attachments: HBASE-14186.patch
>
>
> {code}
> for (int idx = 0; idx < remaining; idx++) {
> byte b = blockBuffer.getByteAfterPosition(offsetFromPos + idx);
> i = i << 8;
> i = i | (b & 0xFF);
> }
> {code}
> Doing the read as in case of BIG_ENDIAN.
> After HBASE-12600, we tend to keep the mvcc and so byte by byte read looks
> eating up lot of CPU time. (In my test HFileReaderImpl#_readMvccVersion comes
> on top in terms of hot methods). We can optimize here by reading 4 or 2 bytes
> in one shot when the length of the vlong is more than 4 bytes. We will in
> turn use UnsafeAccess methods which handles ENDIAN.
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