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https://issues.apache.org/jira/browse/HBASE-390?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Bryan Duxbury resolved HBASE-390.
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Resolution: Duplicate
This has already been done in HADOOP-2532.
> Add getClosestBefore method to MapFile.Reader
> ---------------------------------------------
>
> Key: HBASE-390
> URL: https://issues.apache.org/jira/browse/HBASE-390
> Project: Hadoop HBase
> Issue Type: Bug
> Reporter: Bryan Duxbury
>
> I have been taking a look at HADOOP-2443, using a sparse cache of HBase
> regions. My plan was to implement this ticket by doing point searches in the
> HBase ROOT and META regions as need be. In order to facilitate this, I need a
> method that will get me the closest key to a given key, but in the less than
> direction. That is, it should find the key that either matches exactly or is
> precisely prior to where it should be. This is necessary because in order to
> find where a given row key belongs in an HBase table, you need to compare it
> to the start keys of all the regions.
> The problem lies in the fact that MapFile.Reader, which stores the ROOT and
> META tables, only support searching in the greater-than-or-equal-to sense.
> With this kind of search, we would always end up exactly one position behind
> the region we're actually looking for. Since there is no back() method to
> readjust, this method would not help us. Basically our only option becomes
> doing a linear search through the MapFile to find the key we're looking for,
> which would carry a significant performance penalty in large regions.
> I propose adding a getClosestBefore method that returns the key immediately
> before the the switch from less than or equal to greater than, thus capturing
> the needed key/value.
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