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https://issues.apache.org/jira/browse/HADOOP-2604?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12559105#action_12559105
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Tom White commented on HADOOP-2604:
-----------------------------------
The current design of MapFile.Reader makes it difficult to write an in-memory
implementation. For example, to implement next() it's no good having a copy of
the keys and values in memory as you can't copy their values into the Writables
passed into the next method. Perhaps Writable should have a
readFields(Writable) method? Or maybe the API should change.
To write an in-memory implementation with the current design, I think you would
need to do it at a lower level and hold the data file bytes in memory. Keys and
values would be reconstructed each time next() or get() was called, so this
would be less efficient than an implementation that cached keys and values.
> [hbase] Create an HBase-specific MapFile implementation
> -------------------------------------------------------
>
> Key: HADOOP-2604
> URL: https://issues.apache.org/jira/browse/HADOOP-2604
> Project: Hadoop
> Issue Type: Improvement
> Components: contrib/hbase
> Reporter: Bryan Duxbury
> Priority: Minor
>
> Today, HBase uses the Hadoop MapFile class to store data persistently to
> disk. This is convenient, as it's already done (and maintained by other
> people :). However, it's beginning to look like there might be possible
> performance benefits to be had from doing an HBase-specific implementation of
> MapFile that incorporated some precise features.
> This issue should serve as a place to track discussion about what features
> might be included in such an implementation.
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