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https://issues.apache.org/jira/browse/HBASE-8073?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14492013#comment-14492013
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Anoop Sam John commented on HBASE-8073:
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Seems the approach in V2 is ok. It allows to specify the splits as well as
other imp table/cf attributes like compression, block size etc. The DFS level
read would have allowed it to be read by code, but the user permission can be
really an issue. As this change allows to pass the splits, one can have a
smarter i/p data sampler code sit in front and make the splits as pass to
configureIncrementalLoad().
> HFileOutputFormat support for offline operation
> -----------------------------------------------
>
> Key: HBASE-8073
> URL: https://issues.apache.org/jira/browse/HBASE-8073
> Project: HBase
> Issue Type: Sub-task
> Components: mapreduce
> Reporter: Nick Dimiduk
> Fix For: 1.1.0
>
> Attachments: HBASE-8073-trunk-v0.patch, HBASE-8073-trunk-v1.patch
>
>
> When using HFileOutputFormat to generate HFiles, it inspects the region
> topology of the target table. The split points from that table are used to
> guide the TotalOrderPartitioner. If the target table does not exist, it is
> first created. This imposes an unnecessary dependence on an online HBase and
> existing table.
> If the table exists, it can be used. However, the job can be smarter. For
> example, if there's far more data going into the HFiles than the table
> currently contains, the table regions aren't very useful for data split
> points. Instead, the input data can be sampled to produce split points more
> meaningful to the dataset. LoadIncrementalHFiles is already capable of
> handling divergence between HFile boundaries and table regions, so this
> should not pose any additional burdon at load time.
> The proper method of sampling the data likely requires a custom input format
> and an additional map-reduce job perform the sampling. See a relevant
> implementation:
> https://github.com/alexholmes/hadoop-book/blob/master/src/main/java/com/manning/hip/ch4/sampler/ReservoirSamplerInputFormat.java
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