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https://issues.apache.org/jira/browse/HBASE-4489?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13115051#comment-13115051
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Dave Revell commented on HBASE-4489:
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Mingjie, I would agree with you if the existing behavior was sane, but it has
some problems:
1. Using ASCII strings as keys is a poor choice, and to have it be a default in
a builtin tool would send the wrong message. Since HFiles repeat the key for
every cell in the table, small key size is very important.
2. The MD5StringSplit class contains a bug that makes the current behavior even
less sane. It assumes that an ASCII hex representation of an MD5 hash begins
with 0, 1, 2, 3, 4, 5, 6, or 7. This is incorrect, since an MD5 hash is just a
128-bit number and can start with any digit. The result will be a single
oversized region at the high end of the key space.
So as far as I can tell, the existing behavior does the wrong thing, and
furthermore does it wrongly. We shouldn't preserve this situation.
If I've misunderstood the situation I definitely welcome corrections.
> Better key splitting in RegionSplitter
> --------------------------------------
>
> Key: HBASE-4489
> URL: https://issues.apache.org/jira/browse/HBASE-4489
> Project: HBase
> Issue Type: Improvement
> Affects Versions: 0.90.4
> Reporter: Dave Revell
> Assignee: Dave Revell
> Attachments: HBASE-4489-branch0.90-v1.patch, HBASE-4489-trunk-v1.patch
>
>
> The RegionSplitter utility allows users to create a pre-split table from the
> command line or do a rolling split on an existing table. It supports
> pluggable split algorithms that implement the SplitAlgorithm interface. The
> only/default SplitAlgorithm is one that assumes keys fall in the range from
> ASCII string "00000000" to ASCII string "7FFFFFFF". This is not a sane
> default, and seems useless to most users. Users are likely to be surprised by
> the fact that all the region splits occur in in the byte range of ASCII
> characters.
> A better default split algorithm would be one that evenly divides the space
> of all bytes, which is what this patch does. Making a table with five regions
> would split at \x33\x33..., \x66\x66...., \x99\x99..., \xCC\xCC..., and
> \xFF\xFF.
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