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https://issues.apache.org/jira/browse/HBASE-15477?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15206387#comment-15206387
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stack commented on HBASE-15477:
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We do not write the next blocks header to the cache. I removed that. We do
write an extra 13 bytes beyond the hfileblock bytes themselves... and in these
13 bytes we include length of the next block (I did not change this, i just
documented what is happening and gave the methods and data members used names
that make it clear what is going on -- previous they were called "EXTRA" info).
> Do not save 'next block header' when we cache hfileblocks
> ---------------------------------------------------------
>
> Key: HBASE-15477
> URL: https://issues.apache.org/jira/browse/HBASE-15477
> Project: HBase
> Issue Type: Sub-task
> Components: BlockCache, Performance
> Reporter: stack
> Assignee: stack
> Attachments: 15366v4.patch, 15477.patch, 15477v2.patch,
> 15477v3.patch, 15477v3.patch, 15477v4.patch
>
>
> When we read from HDFS, we overread to pick up the next blocks header.
> Doing this saves a seek as we move through the hfile; we save having to
> do an explicit seek just to read the block header every time we need to
> read the body. We used to read in the next header as part of the
> current blocks buffer. This buffer was then what got persisted to
> blockcache; so we were over-persisting wrtiting out our block plus the
> next blocks' header (overpersisting 33 bytes). Parse of HFileBlock
> complicated by this extra tail. Fix.
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